最近在做gps相关工作，需要解析gps模组输出的nmea数据，获得经纬度等信息，整理了一下nmea各个字段的含义，供大家参考。
基本介绍
GNSS的全称是全球导航卫星系统（Global Navigation Satellite System），它是泛指所有的卫星导航系统，包括全球的、区域的和增强的，如美国的GPS、俄罗斯的Glonass、欧洲的Galileo、中国的北斗卫星导航系统，以及相关的增强系统，如美国的WAAS（广域增强系统）、欧洲的EGNOS（欧洲静地导航重叠系统）和日本的MSAS（多功能运输卫星增强系统）等，还涵盖在建和以后要建设的其他卫星导航系统。国际GNSS系统是个多系统、多层面、多模式的复杂组合系统，如下图所示。
NMEA的全称是美国国家海洋电子协会（National Marine Electronics Association），现在是GPS导航设备统一的RTCM(Radio Technical Commission for Maritime services)标准协议。
NMEA-0183协议定义的语句非常多，但是常用的或者说兼容性最广的语句只有GGA、GSA、GSV、RMC、VTG、GLL等。下面给出这些常用NMEA-0183语句的字段定义解释，此外还有GARMIN定义的扩展语句，本文不做阐述。
NMEA示例
下面是一包完整的nmea报文
$GPGSV,3,1,09,16,26,218,19,29,29,071,38,31,66,027,33,32,40,140,24,1*63
$GPGSV,3,2,09,03,28,291,,04,10,313,,22,29,265,,25,16,046,,1*63
$GPGSV,3,3,09,26,68,223,,1*54
$GPGSV,1,1,01,32,40,140,26,8*58
$GLGSV,3,1,09,66,25,169,30,77,60,003,28,76,18,047,25,87,03,115,23,1*72
$GLGSV,3,2,09,85,03,014,26,67,70,226,20,68,38,321,33,78,39,264,,1*7D
$GLGSV,3,3,09,86,12,057,,1*4E
$GAGSV,2,1,07,05,24,146,23,24,12,048,25,25,67,039,35,02,57,236,,7*75
$GAGSV,2,2,07,03,75,184,,08,43,310,,30,07,231,,7*41
$GAGSV,1,1,03,05,24,146,30,25,67,039,33,24,12,048,,1*40
$GQGSV,1,1,03,01,36,159,29,02,73,090,28,03,15,143,,1*50
$GQGSV,1,1,03,01,36,159,28,02,73,090,30,03,15,143,,8*51
$GBGSV,8,1,30,59,39,145,26,45,05,067,24,44,09,141,28,39,73,100,19,1*7D
$GBGSV,8,2,30,35,18,090,32,29,07,043,23,26,56,045,37,25,09,258,21,1*72
$GBGSV,8,3,30,21,06,166,21,16,79,067,30,09,71,329,31,06,81,011,26,1*7C
$GBGSV,8,4,30,05,15,248,25,04,26,124,29,01,36,140,35,02,33,226,,1*7E
$GBGSV,8,5,30,03,42,190,,07,47,199,,10,34,207,,14,55,242,,1*72
$GBGSV,8,6,30,24,62,286,,33,46,287,,40,55,184,,41,07,324,,1*74
$GBGSV,8,7,30,42,45,202,,56,50,233,,57,09,038,,58,46,088,,1*76
$GBGSV,8,8,30,60,28,228,,61,44,190,,1*7E
$GNGSA,A,3,16,29,31,32,,,,,,,,,1.2,1.0,0.8,1*34
$GNGSA,A,3,66,68,,,,,,,,,,,1.2,1.0,0.8,2*36
$GNGSA,A,3,05,25,,,,,,,,,,,1.2,1.0,0.8,3*3B
$GNGSA,A,3,16,26,35,39,,,,,,,,,1.2,1.0,0.8,4*31
$GNGSA,A,3,01,02,,,,,,,,,,,1.2,1.0,0.8,5*3C
$GNVTG,,T,,M,0.0,N,0.0,K,A*3D
$GNDTM,P90,,0000.000025,S,00000.000002,W,0.981,W84*49
$GNRMC,082923.00,A,3901.106815,N,11712.322006,E,0.0,,231121,5.8,W,A,V*61
$GNGNS,082923.00,3901.106815,N,11712.322006,E,AAAAA,14,1.0,60.6,-4.0,,,V*4D
$GNGGA,082923.00,3901.106815,N,11712.322006,E,1,12,1.0,60.6,M,-4.0,M,,*5A
NMEA解析
1、GP、GL、GA、GQ、GB、GN说明
GP (GPS)
GL (GLONASS)
GA (Galileo)
GQ (QZSS)
GB (Beidou)
GN (Any combination GNSS)，表示使用了多个系统的卫星取得位置解算
2、GSV(可见卫星信息)
例:$GPGSV,3,1,09,16,26,218,19,29,29,071,38,31,66,027,33,32,40,140,24,163
字段0：$GPGSV，语句ID，表明该语句为GPS Satellites in View（GSV）可见卫星信息
字段1：本次GSV语句的总数目（1 - 3）
字段2：本条GSV语句是本次GSV语句的第几条（1 - 3）
字段3：当前可见卫星总数（00 - 12）（前导位数不足则补0）
字段4：PRN 码（伪随机噪声码）（01 - 32）（前导位数不足则补0）
字段5：卫星仰角（00 - 90）度（前导位数不足则补0）
字段6：卫星方位角（00 - 359）度（前导位数不足则补0）
字段7：信噪比（00－99）dbHz
字段8：PRN 码（伪随机噪声码）（01 - 32）（前导位数不足则补0）
字段9：卫星仰角（00 - 90）度（前导位数不足则补0）
字段10：卫星方位角（00 - 359）度（前导位数不足则补0）
字段11：信噪比（00－99）dbHz
字段12：PRN 码（伪随机噪声码）（01 - 32）（前导位数不足则补0）
字段13：卫星仰角（00 - 90）度（前导位数不足则补0）
字段14：卫星方位角（00 - 359）度（前导位数不足则补0）
字段15：信噪比（00－99）dbHz
字段16：校验值（$与之间的数异或后的值）
3、GSA（ 当前卫星信息）
例：$GNGSA,A,3,16,29,31,32,1.2,1.0,0.8,134
字段0：$GPGSA，语句ID，表明该语句为GPS DOP and Active Satellites（GSA）当前卫星信息
字段1：定位模式(选择2D/3D)，A=自动选择，M=手动选择
字段2：定位类型，1=未定位，2=2D定位，3=3D定位
字段3：PRN码（伪随机噪声码），第1信道正在使用的卫星PRN码编号（00）（前导位数不足则补0）
字段4：PRN码（伪随机噪声码），第2信道正在使用的卫星PRN码编号（00）（前导位数不足则补0）
字段5：PRN码（伪随机噪声码），第3信道正在使用的卫星PRN码编号（00）（前导位数不足则补0）
字段6：PRN码（伪随机噪声码），第4信道正在使用的卫星PRN码编号（00）（前导位数不足则补0）
字段7：PRN码（伪随机噪声码），第5信道正在使用的卫星PRN码编号（00）（前导位数不足则补0）
字段8：PRN码（伪随机噪声码），第6信道正在使用的卫星PRN码编号（00）（前导位数不足则补0）
字段9：PRN码（伪随机噪声码），第7信道正在使用的卫星PRN码编号（00）（前导位数不足则补0）
字段10：PRN码（伪随机噪声码），第8信道正在使用的卫星PRN码编号（00）（前导位数不足则补0）
字段11：PRN码（伪随机噪声码），第9信道正在使用的卫星PRN码编号（00）（前导位数不足则补0）
字段12：PRN码（伪随机噪声码），第10信道正在使用的卫星PRN码编号（00）（前导位数不足则补0）
字段13：PRN码（伪随机噪声码），第11信道正在使用的卫星PRN码编号（00）（前导位数不足则补0）
字段14：PRN码（伪随机噪声码），第12信道正在使用的卫星PRN码编号（00）（前导位数不足则补0）
字段15：PDOP综合位置精度因子（0.5 - 99.9）
字段16：HDOP水平精度因子（0.5 - 99.9）
字段17：VDOP垂直精度因子（0.5 - 99.9）
字段18：校验值（$与之间的数异或后的值）
4、RMC（推荐定位信息数据格式）
例：$GNRMC,082923.00,A,3901.106815,N,11712.322006,E,0.0,231121,5.8,W,A,V61
字段0：$GPRMC，语句ID，表明该语句为Recommended Minimum Specific GPS/TRANSIT Data（RMC）推荐最小定位信息
字段1：UTC时间，hhmmss.sss格式
字段2：状态，A=定位，V=未定位
字段3：纬度ddmm.mmmm，度分格式（前导位数不足则补0）
字段4：纬度N（北纬）或S（南纬）
字段5：经度dddmm.mmmm，度分格式（前导位数不足则补0）
字段6：经度E（东经）或W（西经）
字段7：速度，节，Knots
字段8：方位角，度
字段9：UTC日期，DDMMYY格式
字段10：磁偏角，（000 - 180）度（前导位数不足则补0）
字段11：磁偏角方向，E=东W=西
字段12： 模式指示（仅NMEA0183 3.00版本输出，A=自主定位，D=差分，E=估算，N=数据无效）
字段13：校验值（$与之间的数异或后的值）
5、GNS（定位信息）
例：$GNGNS,082923.00,3901.106815,N,11712.322006,E,AAAAA,14,1.0,60.6,-4.0,V4D
字段0：$GNGNS，语句ID，表明该语句为Global Positioning System Fix Data（GNS）GPS定位信息
字段1：UTC 时间，hhmmss.sss，时分秒格式
字段2：纬度ddmm.mmmm，度分格式（前导位数不足则补0）
字段3：纬度N（北纬）或S（南纬）
字段4：经度dddmm.mmmm，度分格式（前导位数不足则补0）
字段5：经度E（东经）或W（西经）
字段6：定位标识，NN - 未定位，AA - 定位Active
字段7：正在使用的卫星数量（00 - 12）（前导位数不足则补0）
字段8：HDOP水平精度因子（0.5 - 99.9）
字段9：海拔高度（-9999.9 - 99999.9）单位：M（米）
字段10：地球椭球面相对大地水准面的高度 WGS84水准面划分 单位：M（米）
字段11：差分时间（从接收到差分信号开始的秒数，如果不是差分定位将为空）
字段12：差分站ID号0000 - 1023（前导位数不足则补0，如果不是差分定位将为空）
字段13：校验值（$与之间的数异或后的值）
6、GGA（定位信息）
例：$GNGGA,082923.00,3901.106815,N,11712.322006,E,1,12,1.0,60.6,M,-4.0,M,5A
字段0：$GPGGA，语句ID，表明该语句为Global Positioning System Fix Data（GGA）GPS定位信息
字段1：UTC 时间，hhmmss.sss，时分秒格式
字段2：纬度ddmm.mmmm，度分格式（前导位数不足则补0）
字段3：纬度N（北纬）或S（南纬）
字段4：经度dddmm.mmmm，度分格式（前导位数不足则补0）
字段5：经度E（东经）或W（西经）
字段6：GPS状态，0=不可用(FIX NOT valid)，1=单点定位(GPS FIX)，2=差分定位(DGPS)，3=无效PPS，4=实时差分定位（RTK FIX），5=RTK FLOAT，6=正在估算
字段7：正在使用的卫星数量（00 - 12）（前导位数不足则补0）
字段8：HDOP水平精度因子（0.5 - 99.9）
字段9：海拔高度（-9999.9 - 99999.9）
字段10：海拔高度 单位：M（米）
字段11：地球椭球面相对大地水准面的高度 WGS84水准面划分
字段12：WGS84水准面划分 单位：M（米）
字段13：差分时间（从接收到差分信号开始的秒数，如果不是差分定位将为空）
字段14：差分站ID号0000 - 1023（前导位数不足则补0，如果不是差分定位将为空）
字段15：校验值（$与之间的数异或后的值）
7、GLL（地理定位信息）
例：$GNGLL,4250.5589,S,14718.5084,E,092204.999,A2D
字段0：$GNGLL，语句ID，表明该语句为Geographic Position（GLL）地理定位信息
字段1：纬度ddmm.mmmm，度分格式（前导位数不足则补0）
字段2：纬度N（北纬）或S（南纬）
字段3：经度dddmm.mmmm，度分格式（前导位数不足则补0）
字段4：经度E（东经）或W（西经）
字段5：UTC时间，hhmmss.sss格式
字段6：状态，A=定位，V=未定位
字段7：校验值（$与之间的数异或后的值）
8、VTG（地面速度信息）
例：$GNVTG,T,M,0.0,N,0.0,K,A3D
字段0：$GPVTG，语句ID，表明该语句为Track Made Good and Ground Speed（VTG）地面速度信息
字段1：运动角度，000 - 359，（前导位数不足则补0）
字段2：T=真北参照系
字段3：运动角度，000 - 359，（前导位数不足则补0）
字段4：M=磁北参照系
字段5：水平运动速度（0.00）（前导位数不足则补0）
字段6：N=节，Knots
字段7：水平运动速度（0.00）（前导位数不足则补0）
字段8：K=公里/时，km/h
字段9：校验值（$与之间的数异或后的值）
9、ZDA（时间和日期信息）
例：$GNZDA,160012.71,11,03,2004,-1,007D
字段0：$GNZDA，语句ID，表明该语句为Data and time（ZDA）时间和日期信息
字段1：UTC时间，hhmmss（时分秒）格式
字段2：UTC日期，日
字段3：UTC日期，月
字段4：UTC日期，年
字段5：时区
字段6：校验值（$与之间的数异或后的值）
10、DTM（大地坐标系信息）
例：$GNDTM,P90,0000.000025,S,00000.000002,W,0.981,W8449
字段0：$GNDTM，语句ID，表明该语句为Datum（DTM）大地坐标系信息
字段1：本地坐标系代码 W84
字段2：坐标系子代码 空
字段3：纬度偏移量
字段4：纬度半球N（北半球）或S（南半球）
字段5：经度偏移量
字段6：经度半球E（东经）或W（西经）
字段7：高度偏移量
字段8：坐标系代码 W84
字段9：校验值（$与之间的数异或后的值）
NMEA解析C程序
引用自开源程序代码gpsd-3.16，仅供参考。
driver_nmea0183.c
/* * This file is Copyright (c) 2010 by the GPSD project * BSD terms apply: see the file COPYING in the distribution root for details. */
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <math.h>
#include <string.h>
#include <stdarg.h>
#include <time.h>
#include "gpsd.h"
#include "strfuncs.h"
#ifdef NMEA0183_ENABLE
/************************************************************************** * * Parser helpers begin here * **************************************************************************/
static void do_lat_lon(char *field[], struct gps_fix_t *out)
/* process a pair of latitude/longitude fields starting at field index BEGIN */
{
double d, m;
char str[20], *p;
if (*(p = field[0]) != '\0') {
double lat;
(void)strlcpy(str, p, sizeof(str));
lat = atof(str);
m = 100.0 * modf(lat / 100.0, &d);
lat = d + m / 60.0;
p = field[1];
if (*p == 'S')
lat = -lat;
out->latitude = lat;
}
if (*(p = field[2]) != '\0') {
double lon;
(void)strlcpy(str, p, sizeof(str));
lon = atof(str);
m = 100.0 * modf(lon / 100.0, &d);
lon = d + m / 60.0;
p = field[3];
if (*p == 'W')
lon = -lon;
out->longitude = lon;
}
}
/************************************************************************** * * Scary timestamp fudging begins here * * Four sentences, GGA and GLL and RMC and ZDA, contain timestamps. * GGA/GLL/RMC timestamps look like hhmmss.ss, with the trailing .ss * part optional. RMC has a date field, in the format ddmmyy. ZDA * has separate fields for day/month/year, with a 4-digit year. This * means that for RMC we must supply a century and for GGA and GLL we * must supply a century, year, and day. We get the missing data from * a previous RMC or ZDA; century in RMC is supplied from the daemon's * context (initialized at startup time) if there has been no previous * ZDA. * **************************************************************************/
#define DD(s) ((int)((s)[0]-'0')*10+(int)((s)[1]-'0'))
static void merge_ddmmyy(char *ddmmyy, struct gps_device_t *session)
/* sentence supplied ddmmyy, but no century part */
{
int yy = DD(ddmmyy + 4);
int mon = DD(ddmmyy + 2);
int mday = DD(ddmmyy);
int year;
/* check for century wrap */
if (session->nmea.date.tm_year % 100 == 99 && yy == 0)
gpsd_century_update(session, session->context->century + 100);
year = (session->context->century + yy);
if ( (1 > mon ) || (12 < mon ) ) {
gpsd_log(&session->context->errout, LOG_WARN,
"merge_ddmmyy(%s), malformed month\n", ddmmyy);
} else if ( (1 > mday ) || (31 < mday ) ) {
gpsd_log(&session->context->errout, LOG_WARN,
"merge_ddmmyy(%s), malformed day\n", ddmmyy);
} else {
gpsd_log(&session->context->errout, LOG_DATA,
"merge_ddmmyy(%s) sets year %d\n",
ddmmyy, year);
session->nmea.date.tm_year = year - 1900;
session->nmea.date.tm_mon = mon - 1;
session->nmea.date.tm_mday = mday;
}
}
static void merge_hhmmss(char *hhmmss, struct gps_device_t *session)
/* update from a UTC time */
{
int old_hour = session->nmea.date.tm_hour;
session->nmea.date.tm_hour = DD(hhmmss);
if (session->nmea.date.tm_hour < old_hour) /* midnight wrap */
session->nmea.date.tm_mday++;
session->nmea.date.tm_min = DD(hhmmss + 2);
session->nmea.date.tm_sec = DD(hhmmss + 4);
session->nmea.subseconds =
safe_atof(hhmmss + 4) - session->nmea.date.tm_sec;
}
static void register_fractional_time(const char *tag, const char *fld,
struct gps_device_t *session)
{
if (fld[0] != '\0') {
session->nmea.last_frac_time =
session->nmea.this_frac_time;
session->nmea.this_frac_time = safe_atof(fld);
session->nmea.latch_frac_time = true;
gpsd_log(&session->context->errout, LOG_DATA,
"%s: registers fractional time %.2f\n",
tag, session->nmea.this_frac_time);
}
}
/************************************************************************** * * Compare GPS timestamps for equality. Depends on the fact that the * timestamp granularity of GPS is 1/100th of a second. Use this to avoid * naive float comparisons. * **************************************************************************/
#define GPS_TIME_EQUAL(a, b) (fabs((a) - (b)) < 0.01)
/************************************************************************** * * NMEA sentence handling begins here * **************************************************************************/
static gps_mask_t processRMC(int count, char *field[],
struct gps_device_t *session)
/* Recommend Minimum Course Specific GPS/TRANSIT Data */
{
/* * RMC,225446.33,A,4916.45,N,12311.12,W,000.5,054.7,191194,020.3,E,A*68 * 1 225446.33 Time of fix 22:54:46 UTC * 2 A Status of Fix: A = Autonomous, valid; * D = Differential, valid; V = invalid * 3,4 4916.45,N Latitude 49 deg. 16.45 min North * 5,6 12311.12,W Longitude 123 deg. 11.12 min West * 7 000.5 Speed over ground, Knots * 8 054.7 Course Made Good, True north * 9 181194 Date of fix 18 November 1994 * 10,11 020.3,E Magnetic variation 20.3 deg East * 12 A FAA mode indicator (NMEA 2.3 and later) * A=autonomous, D=differential, E=Estimated, * N=not valid, S=Simulator, M=Manual input mode * *68 mandatory nmea_checksum * * * SiRF chipsets don't return either Mode Indicator or magnetic variation. */
gps_mask_t mask = 0;
if (strcmp(field[2], "V") == 0) {
/* copes with Magellan EC-10X, see below */
if (session->gpsdata.status != STATUS_NO_FIX) {
session->gpsdata.status = STATUS_NO_FIX;
mask |= STATUS_SET;
}
if (session->newdata.mode >= MODE_2D) {
session->newdata.mode = MODE_NO_FIX;
mask |= MODE_SET;
}
/* set something nz, so it won't look like an unknown sentence */
mask |= ONLINE_SET;
} else if (strcmp(field[2], "A") == 0) {
/* * The MTK3301, Royaltek RGM-3800, and possibly other * devices deliver bogus time values when the navigation * warning bit is set. */
if (count > 9 && field[1][0] != '\0' && field[9][0] != '\0') {
merge_hhmmss(field[1], session);
merge_ddmmyy(field[9], session);
mask |= TIME_SET;
register_fractional_time(field[0], field[1], session);
}
do_lat_lon(&field[3], &session->newdata);
mask |= LATLON_SET;
session->newdata.speed = safe_atof(field[7]) * KNOTS_TO_MPS;
session->newdata.track = safe_atof(field[8]);
mask |= (TRACK_SET | SPEED_SET);
/* * This copes with GPSes like the Magellan EC-10X that *only* emit * GPRMC. In this case we set mode and status here so the client * code that relies on them won't mistakenly believe it has never * received a fix. */
if (session->gpsdata.status == STATUS_NO_FIX) {
session->gpsdata.status = STATUS_FIX; /* could be DGPS_FIX, we can't tell */
mask |= STATUS_SET;
}
if (session->newdata.mode < MODE_2D) {
session->newdata.mode = MODE_2D;
mask |= MODE_SET;
}
}
gpsd_log(&session->context->errout, LOG_DATA,
"RMC: ddmmyy=%s hhmmss=%s lat=%.2f lon=%.2f "
"speed=%.2f track=%.2f mode=%d status=%d\n",
field[9], field[1],
session->newdata.latitude,
session->newdata.longitude,
session->newdata.speed,
session->newdata.track,
session->newdata.mode,
session->gpsdata.status);
return mask;
}
static gps_mask_t processGLL(int count, char *field[],
struct gps_device_t *session)
/* Geographic position - Latitude, Longitude */
{
/* Introduced in NMEA 3.0. * * $GPGLL,4916.45,N,12311.12,W,225444,A,A*5C * * 1,2: 4916.46,N Latitude 49 deg. 16.45 min. North * 3,4: 12311.12,W Longitude 123 deg. 11.12 min. West * 5: 225444 Fix taken at 22:54:44 UTC * 6: A Data valid * 7: A Autonomous mode * 8: *5C Mandatory NMEA checksum * * 1,2 Latitude, N (North) or S (South) * 3,4 Longitude, E (East) or W (West) * 5 UTC of position * 6 A=Active, V=Void * 7 Mode Indicator * A = Autonomous mode * D = Differential Mode * E = Estimated (dead-reckoning) mode * M = Manual Input Mode * S = Simulated Mode * N = Data Not Valid * * I found a note at <http://www.secoh.ru/windows/gps/nmfqexep.txt> * indicating that the Garmin 65 does not return time and status. * SiRF chipsets don't return the Mode Indicator. * This code copes gracefully with both quirks. * * Unless you care about the FAA indicator, this sentence supplies nothing * that GPRMC doesn't already. But at least one Garmin GPS -- the 48 * actually ships updates in GLL that aren't redundant. */
char *status = field[7];
gps_mask_t mask = 0;
if (field[5][0] != '\0') {
merge_hhmmss(field[5], session);
register_fractional_time(field[0], field[5], session);
if (session->nmea.date.tm_year == 0)
gpsd_log(&session->context->errout, LOG_WARN,
"can't use GLL time until after ZDA or RMC has supplied a year.\n");
else {
mask = TIME_SET;
}
}
if (strcmp(field[6], "A") == 0 && (count < 8 || *status != 'N')) {
int newstatus;
do_lat_lon(&field[1], &session->newdata);
mask |= LATLON_SET;
if (count >= 8 && *status == 'D')
newstatus = STATUS_DGPS_FIX; /* differential */
else
newstatus = STATUS_FIX;
/* * This is a bit dodgy. Technically we shouldn't set the mode * bit until we see GSA. But it may be later in the cycle, * some devices like the FV-18 don't send it by default, and * elsewhere in the code we want to be able to test for the * presence of a valid fix with mode > MODE_NO_FIX. */
if (session->newdata.mode < MODE_2D) {
session->newdata.mode = MODE_2D;
mask |= MODE_SET;
}
session->gpsdata.status = newstatus;
mask |= STATUS_SET;
}
gpsd_log(&session->context->errout, LOG_DATA,
"GLL: hhmmss=%s lat=%.2f lon=%.2f mode=%d status=%d\n",
field[5],
session->newdata.latitude,
session->newdata.longitude,
session->newdata.mode,
session->gpsdata.status);
return mask;
}
static gps_mask_t processGGA(int c UNUSED, char *field[],
struct gps_device_t *session)
/* Global Positioning System Fix Data */
{
/* * GGA,123519,4807.038,N,01131.324,E,1,08,0.9,545.4,M,46.9,M, , *42 * 1 123519 Fix taken at 12:35:19 UTC * 2,3 4807.038,N Latitude 48 deg 07.038' N * 4,5 01131.324,E Longitude 11 deg 31.324' E * 6 1 Fix quality: 0 = invalid, 1 = GPS, 2 = DGPS, * 3=PPS (Precise Position Service), * 4=RTK (Real Time Kinematic) with fixed integers, * 5=Float RTK, 6=Estimated, 7=Manual, 8=Simulator * 7 08 Number of satellites being tracked * 8 0.9 Horizontal dilution of position * 9,10 545.4,M Altitude, Metres above mean sea level * 11,12 46.9,M Height of geoid (mean sea level) above WGS84 * ellipsoid, in Meters * (empty field) time in seconds since last DGPS update * (empty field) DGPS station ID number (0000-1023) */
gps_mask_t mask;
session->gpsdata.status = atoi(field[6]);
mask = STATUS_SET;
/* * There are some receivers (the Trimble Placer 450 is an example) that * don't ship a GSA with mode 1 when they lose satellite lock. Instead * they just keep reporting GGA and GSA on subsequent cycles with the * timestamp not advancing and a bogus mode. On the assumption that GGA * is only issued once per cycle we can detect this here (it would be * nicer to do it on GSA but GSA has no timestamp). */
session->nmea.latch_mode = strncmp(field[1],
session->nmea.last_gga_timestamp,
sizeof(session->nmea.last_gga_timestamp))==0;
if (session->nmea.latch_mode) {
session->gpsdata.status = STATUS_NO_FIX;
session->newdata.mode = MODE_NO_FIX;
} else
(void)strlcpy(session->nmea.last_gga_timestamp,
field[1],
sizeof(session->nmea.last_gga_timestamp));
/* if we have a fix and the mode latch is off, go... */
if (session->gpsdata.status > STATUS_NO_FIX) {
char *altitude;
merge_hhmmss(field[1], session);
register_fractional_time(field[0], field[1], session);
if (session->nmea.date.tm_year == 0)
gpsd_log(&session->context->errout, LOG_WARN,
"can't use GGA time until after ZDA or RMC has supplied a year.\n");
else {
mask |= TIME_SET;
}
do_lat_lon(&field[2], &session->newdata);
mask |= LATLON_SET;
session->gpsdata.satellites_used = atoi(field[7]);
altitude = field[9];
/* * SiRF chipsets up to version 2.2 report a null altitude field. * See <http://www.sirf.com/Downloads/Technical/apnt0033.pdf>. * If we see this, force mode to 2D at most. */
if (altitude[0] == '\0') {
if (session->newdata.mode > MODE_2D) {
session->newdata.mode = MODE_2D;
mask |= MODE_SET;
}
} else {
session->newdata.altitude = safe_atof(altitude);
mask |= ALTITUDE_SET;
/* * This is a bit dodgy. Technically we shouldn't set the mode * bit until we see GSA. But it may be later in the cycle, * some devices like the FV-18 don't send it by default, and * elsewhere in the code we want to be able to test for the * presence of a valid fix with mode > MODE_NO_FIX. */
if (session->newdata.mode < MODE_3D) {
session->newdata.mode = MODE_3D;
mask |= MODE_SET;
}
}
if (strlen(field[11]) > 0) {
session->gpsdata.separation = safe_atof(field[11]);
} else {
session->gpsdata.separation =
wgs84_separation(session->newdata.latitude,
session->newdata.longitude);
}
}
gpsd_log(&session->context->errout, LOG_DATA,
"GGA: hhmmss=%s lat=%.2f lon=%.2f alt=%.2f mode=%d status=%d\n",
field[1],
session->newdata.latitude,
session->newdata.longitude,
session->newdata.altitude,
session->newdata.mode,
session->gpsdata.status);
return mask;
}
static gps_mask_t processGST(int count, char *field[], struct gps_device_t *session)
/* GST - GPS Pseudorange Noise Statistics */
{
/* * GST,hhmmss.ss,x,x,x,x,x,x,x,*hh * 1 TC time of associated GGA fix * 2 Total RMS standard deviation of ranges inputs to the navigation solution * 3 Standard deviation (meters) of semi-major axis of error ellipse * 4 Standard deviation (meters) of semi-minor axis of error ellipse * 5 Orientation of semi-major axis of error ellipse (true north degrees) * 6 Standard deviation (meters) of latitude error * 7 Standard deviation (meters) of longitude error * 8 Standard deviation (meters) of altitude error * 9 Checksum */
if (count < 8) {
return 0;
}
#define PARSE_FIELD(n) (*field[n]!='\0' ? safe_atof(field[n]) : NAN)
session->gpsdata.gst.utctime = PARSE_FIELD(1);
session->gpsdata.gst.rms_deviation = PARSE_FIELD(2);
session->gpsdata.gst.smajor_deviation = PARSE_FIELD(3);
session->gpsdata.gst.sminor_deviation = PARSE_FIELD(4);
session->gpsdata.gst.smajor_orientation = PARSE_FIELD(5);
session->gpsdata.gst.lat_err_deviation = PARSE_FIELD(6);
session->gpsdata.gst.lon_err_deviation = PARSE_FIELD(7);
session->gpsdata.gst.alt_err_deviation = PARSE_FIELD(8);
#undef PARSE_FIELD
register_fractional_time(field[0], field[1], session);
gpsd_log(&session->context->errout, LOG_DATA,
"GST: utc = %.2f, rms = %.2f, maj = %.2f, min = %.2f, ori = %.2f, lat = %.2f, lon = %.2f, alt = %.2f\n",
session->gpsdata.gst.utctime,
session->gpsdata.gst.rms_deviation,
session->gpsdata.gst.smajor_deviation,
session->gpsdata.gst.sminor_deviation,
session->gpsdata.gst.smajor_orientation,
session->gpsdata.gst.lat_err_deviation,
session->gpsdata.gst.lon_err_deviation,
session->gpsdata.gst.alt_err_deviation);
return GST_SET | ONLINE_SET;
}
static int nmeaid_to_prn(char *talker, int satnum)
/* deal with range-mapping attempts to to use IDs 1-32 by Beidou, etc. */
{
/* * According to https://github.com/mvglasow/satstat/wiki/NMEA-IDs * NMEA IDs can be roughly divided into the following ranges: * * 1..32: GPS * 33..54: Various SBAS systems (EGNOS, WAAS, SDCM, GAGAN, MSAS) * ... some IDs still unused * 55..64: not used (might be assigned to further SBAS systems) * 65..88: GLONASS * 89..96: GLONASS (future extensions?) * 97..192: not used (SBAS PRNs 120-151 fall in here) * 193..195: QZSS * 196..200: QZSS (future extensions?) * 201..235: Beidou * * The issue is what to do when GPSes from these different systems * fight for IDs in the 1-32 range, as in this pair of Beidou sentences * * $BDGSV,2,1,07,01,00,000,45,02,13,089,35,03,00,000,37,04,00,000,42*6E * $BDGSV,2,2,07,05,27,090,,13,19,016,,11,07,147,*5E * * Because the PRNs are only used for generating a satellite * chart, mistakes here aren't dangerous. The code will record * and use multiple sats with the same ID in one skyview; in * effect, they're recorded by the order in which they occur * rather than by PRN. */
// NMEA-ID (33..64) to SBAS PRN 120-151.
if (satnum >= 33 && satnum <= 64)
satnum += 87;
if (satnum < 32) {
/* map Beidou IDs */
if (talker[0] == 'B' && talker[1] == 'D')
satnum += 200;
else if (talker[0] == 'G' && talker[1] == 'B')
satnum += 200;
/* GLONASS GL doesn't seem to do this, but better safe than sorry */
if (talker[0] == 'G' && (talker[1] == 'L' || talker[1] == 'N'))
satnum += 37;
/* QZSS */
if (talker[0] == 'Q' && talker[1] == 'Z')
satnum += 193;
}
return satnum;
}
static gps_mask_t processGSA(int count, char *field[],
struct gps_device_t *session)
/* GPS DOP and Active Satellites */
{
/* * eg1. $GPGSA,A,3,,,,,,16,18,,22,24,,,3.6,2.1,2.2*3C * eg2. $GPGSA,A,3,19,28,14,18,27,22,31,39,,,,,1.7,1.0,1.3*35 * 1 = Mode: * M=Manual, forced to operate in 2D or 3D * A=Automatic, 3D/2D * 2 = Mode: 1=Fix not available, 2=2D, 3=3D * 3-14 = PRNs of satellites used in position fix (null for unused fields) * 15 = PDOP * 16 = HDOP * 17 = VDOP */
gps_mask_t mask;
/* * One chipset called the i.Trek M3 issues GPGSA lines that look like * this: "$GPGSA,A,1,,,,*32" when it has no fix. This is broken * in at least two ways: it's got the wrong number of fields, and * it claims to be a valid sentence (A flag) when it isn't. * Alarmingly, it's possible this error may be generic to SiRFstarIII. */
if (count < 17) {
gpsd_log(&session->context->errout, LOG_DATA,
"GPGSA: malformed, setting ONLINE_SET only.\n");
mask = ONLINE_SET;
} else if (session->nmea.latch_mode) {
/* last GGA had a non-advancing timestamp; don't trust this GSA */
mask = ONLINE_SET;
} else {
int i;
session->newdata.mode = atoi(field[2]);
/* * The first arm of this conditional ignores dead-reckoning * fixes from an Antaris chipset. which returns E in field 2 * for a dead-reckoning estimate. Fix by Andreas Stricker. */
if (session->newdata.mode == 0 && field[2][0] == 'E')
mask = 0;
else
mask = MODE_SET;
gpsd_log(&session->context->errout, LOG_PROG,
"GPGSA sets mode %d\n", session->newdata.mode);
if (field[15][0] != '\0')
session->gpsdata.dop.pdop = safe_atof(field[15]);
if (field[16][0] != '\0')
session->gpsdata.dop.hdop = safe_atof(field[16]);
if (field[17][0] != '\0')
session->gpsdata.dop.vdop = safe_atof(field[17]);
session->gpsdata.satellites_used = 0;
memset(session->nmea.sats_used, 0, sizeof(session->nmea.sats_used));
/* the magic 6 here counts the tag, two mode fields, and the DOP fields */
for (i = 0; i < count - 6; i++) {
int prn = nmeaid_to_prn(field[0], atoi(field[i + 3]));
if (prn > 0)
session->nmea.sats_used[session->gpsdata.satellites_used++] =
(unsigned short)prn;
}
mask |= DOP_SET | USED_IS;
gpsd_log(&session->context->errout, LOG_DATA,
"GPGSA: mode=%d used=%d pdop=%.2f hdop=%.2f vdop=%.2f\n",
session->newdata.mode,
session->gpsdata.satellites_used,
session->gpsdata.dop.pdop,
session->gpsdata.dop.hdop,
session->gpsdata.dop.vdop);
}
return mask;
}
static gps_mask_t processGSV(int count, char *field[],
struct gps_device_t *session)
/* GPS Satellites in View */
{
#define GSV_TALKER field[0][1]
/* * GSV,2,1,08,01,40,083,46,02,17,308,41,12,07,344,39,14,22,228,45*75 * 2 Number of sentences for full data * 1 Sentence 1 of 2 * 08 Total number of satellites in view * 01 Satellite PRN number * 40 Elevation, degrees * 083 Azimuth, degrees * 46 Signal-to-noise ratio in decibels * <repeat for up to 4 satellites per sentence> * There my be up to three GSV sentences in a data packet * * Can occur with talker IDs: * BD (Beidou), * GA (Galileo), * GB (Beidou), * GL (GLONASS), * GN (GLONASS, any combination GNSS), * GP (GPS, SBAS, QZSS), * QZ (QZSS). * * GL may be (incorrectly) used when GSVs are mixed containing * GLONASS, GN may be (incorrectly) used when GSVs contain GLONASS * only. Usage is inconsistent. * * In the GLONASS version sat IDs run from 65-96 (NMEA0183 standardizes * this). At least two GPS, the BU-353 GLONASS and the u-blox NEO-M8N, * emit a GPGSV set followed by a GLGSV set. We have also seen a * SiRF-IV variant that emits GPGSV followed by BDGSV. We need to * combine these. * * NMEA 4.1 adds a signal-ID field just before the checksum. First * seen in May 2015 on a u-blox M8, */
int n, fldnum;
if (count <= 3) {
gpsd_log(&session->context->errout, LOG_WARN,
"malformed GPGSV - fieldcount %d <= 3\n",
count);
gpsd_zero_satellites(&session->gpsdata);
session->gpsdata.satellites_visible = 0;
return ONLINE_SET;
}
/* * This check used to be !=0, but we have loosen it a little to let by * NMEA 4.1 GSVs with an extra signal-ID field at the end. */
if (count % 4 > 1) {
gpsd_log(&session->context->errout, LOG_WARN,
"malformed GPGSV - fieldcount %d %% 4 != 0\n",
count);
gpsd_zero_satellites(&session->gpsdata);
session->gpsdata.satellites_visible = 0;
return ONLINE_SET;
}
session->nmea.await = atoi(field[1]);
if ((session->nmea.part = atoi(field[2])) < 1) {
gpsd_log(&session->context->errout, LOG_WARN,
"malformed GPGSV - bad part\n");
gpsd_zero_satellites(&session->gpsdata);
return ONLINE_SET;
} else if (session->nmea.part == 1) {
/* * might have gone from GPGSV to GLGSV/BDGSV/QZGSV, * in which case accumulate */
if (session->nmea.last_gsv_talker == '\0' || GSV_TALKER == session->nmea.last_gsv_talker) {
gpsd_zero_satellites(&session->gpsdata);
}
session->nmea.last_gsv_talker = GSV_TALKER;
if (session->nmea.last_gsv_talker == 'L')
session->nmea.seen_glgsv = true;
if (session->nmea.last_gsv_talker == 'D')
session->nmea.seen_bdgsv = true;
if (session->nmea.last_gsv_talker == 'Z')
session->nmea.seen_qzss = true;
}
for (fldnum = 4; fldnum < count;) {
struct satellite_t *sp;
if (session->gpsdata.satellites_visible >= MAXCHANNELS) {
gpsd_log(&session->context->errout, LOG_ERROR,
"internal error - too many satellites [%d]!\n",
session->gpsdata.satellites_visible);
gpsd_zero_satellites(&session->gpsdata);
break;
}
sp = &session->gpsdata.skyview[session->gpsdata.satellites_visible];
sp->PRN = (short)nmeaid_to_prn(field[0], atoi(field[fldnum++]));
sp->elevation = (short)atoi(field[fldnum++]);
sp->azimuth = (short)atoi(field[fldnum++]);
sp->ss = (float)atoi(field[fldnum++]);
sp->used = false;
if (sp->PRN > 0)
for (n = 0; n < MAXCHANNELS; n++)
if (session->nmea.sats_used[n] == (unsigned short)sp->PRN) {
sp->used = true;
break;
}
/* * Incrementing this unconditionally falls afoul of chipsets like * the Motorola Oncore GT+ that emit empty fields at the end of the * last sentence in a GPGSV set if the number of satellites is not * a multiple of 4. */
if (sp->PRN != 0)
session->gpsdata.satellites_visible++;
}
/* * Alas, we can't sanity check field counts when there are multiple sat * pictures, because the visible member counts *all* satellites - you * get a bad result on the second and later SV spans. Note, this code * assumes that if any of the special sat pics occur they come right * after a stock GPGSV one. */
if (session->nmea.seen_glgsv || session->nmea.seen_bdgsv || session->nmea.seen_qzss)
if (session->nmea.part == session->nmea.await
&& atoi(field[3]) != session->gpsdata.satellites_visible)
gpsd_log(&session->context->errout, LOG_WARN,
"GPGSV field 3 value of %d != actual count %d\n",
atoi(field[3]), session->gpsdata.satellites_visible);
/* not valid data until we've seen a complete set of parts */
if (session->nmea.part < session->nmea.await) {
gpsd_log(&session->context->errout, LOG_PROG,
"Partial satellite data (%d of %d).\n",
session->nmea.part, session->nmea.await);
return ONLINE_SET;
}
/* * This sanity check catches an odd behavior of SiRFstarII receivers. * When they can't see any satellites at all (like, inside a * building) they sometimes cough up a hairball in the form of a * GSV packet with all the azimuth entries 0 (but nonzero * elevations). This behavior was observed under SiRF firmware * revision 231.000.000_A2. */
for (n = 0; n < session->gpsdata.satellites_visible; n++)
if (session->gpsdata.skyview[n].azimuth != 0)
goto sane;
gpsd_log(&session->context->errout, LOG_WARN,
"Satellite data no good (%d of %d).\n",
session->nmea.part, session->nmea.await);
gpsd_zero_satellites(&session->gpsdata);
return ONLINE_SET;
sane:
session->gpsdata.skyview_time = NAN;
gpsd_log(&session->context->errout, LOG_DATA,
"GSV: Satellite data OK (%d of %d).\n",
session->nmea.part, session->nmea.await);
/* assumes GLGSV or BDGSV group, if present, is emitted after the GPGSV */
if ((session->nmea.seen_glgsv || session->nmea.seen_bdgsv || session->nmea.seen_qzss) && GSV_TALKER == 'P')
return ONLINE_SET;
return SATELLITE_SET;
#undef GSV_TALKER
}
static gps_mask_t processPGRME(int c UNUSED, char *field[],
struct gps_device_t *session)
/* Garmin Estimated Position Error */
{
/* * $PGRME,15.0,M,45.0,M,25.0,M*22 * 1 = horizontal error estimate * 2 = units * 3 = vertical error estimate * 4 = units * 5 = spherical error estimate * 6 = units * * * * Garmin won't say, but the general belief is that these are 50% CEP. * * We follow the advice at <http://gpsinformation.net/main/errors.htm>. * * If this assumption changes here, it should also change in garmin.c * * where we scale error estimates from Garmin binary packets, and * * in libgpsd_core.c where we generate $PGRME. */
gps_mask_t mask;
if ((strcmp(field[2], "M") != 0) ||
(strcmp(field[4], "M") != 0) || (strcmp(field[6], "M") != 0)) {
session->newdata.epx =
session->newdata.epy =
session->newdata.epv = session->gpsdata.epe = 100;
mask = 0;
} else {
session->newdata.epx = session->newdata.epy =
safe_atof(field[1]) * (1 / sqrt(2)) * (GPSD_CONFIDENCE / CEP50_SIGMA);
session->newdata.epv =
safe_atof(field[3]) * (GPSD_CONFIDENCE / CEP50_SIGMA);
session->gpsdata.epe =
safe_atof(field[5]) * (GPSD_CONFIDENCE / CEP50_SIGMA);
mask = HERR_SET | VERR_SET | PERR_IS;
}
gpsd_log(&session->context->errout, LOG_DATA,
"PGRME: epx=%.2f epy=%.2f epv=%.2f\n",
session->newdata.epx,
session->newdata.epy,
session->newdata.epv);
return mask;
}
static gps_mask_t processGBS(int c UNUSED, char *field[],
struct gps_device_t *session)
/* NMEA 3.0 Estimated Position Error */
{
/* * $GPGBS,082941.00,2.4,1.5,3.9,25,,-43.7,27.5*65 * 1) UTC time of the fix associated with this sentence (hhmmss.ss) * 2) Expected error in latitude (meters) * 3) Expected error in longitude (meters) * 4) Expected error in altitude (meters) * 5) PRN of most likely failed satellite * 6) Probability of missed detection for most likely failed satellite * 7) Estimate of bias in meters on most likely failed satellite * 8) Standard deviation of bias estimate * 9) Checksum */
/* register fractional time for end-of-cycle detection */
register_fractional_time(field[0], field[1], session);
/* check that we're associated with the current fix */
if (session->nmea.date.tm_hour == DD(field[1])
&& session->nmea.date.tm_min == DD(field[1] + 2)
&& session->nmea.date.tm_sec == DD(field[1] + 4)) {
session->newdata.epy = safe_atof(field[2]);
session->newdata.epx = safe_atof(field[3]);
session->newdata.epv = safe_atof(field[4]);
gpsd_log(&session->context->errout, LOG_DATA,
"GBS: epx=%.2f epy=%.2f epv=%.2f\n",
session->newdata.epx,
session->newdata.epy,
session->newdata.epv);
return HERR_SET | VERR_SET;
} else {
gpsd_log(&session->context->errout, LOG_PROG,
"second in $GPGBS error estimates doesn't match.\n");
return 0;
}
}
static gps_mask_t processZDA(int c UNUSED, char *field[],
struct gps_device_t *session)
/* Time & Date */
{
/* * $GPZDA,160012.71,11,03,2004,-1,00*7D * 1) UTC time (hours, minutes, seconds, may have fractional subsecond) * 2) Day, 01 to 31 * 3) Month, 01 to 12 * 4) Year (4 digits) * 5) Local zone description, 00 to +- 13 hours * 6) Local zone minutes description, apply same sign as local hours * 7) Checksum * * Note: some devices, like the u-blox ANTARIS 4h, are known to ship ZDAs * with some fields blank under poorly-understood circumstances (probably * when they don't have satellite lock yet). */
gps_mask_t mask = 0;
if (field[1][0] == '\0' || field[2][0] == '\0' || field[3][0] == '\0'
|| field[4][0] == '\0') {
gpsd_log(&session->context->errout, LOG_WARN, "ZDA fields are empty\n");
} else {
int year, mon, mday, century;
merge_hhmmss(field[1], session);
/* * We don't register fractional time here because want to leave * ZDA out of end-of-cycle detection. Some devices sensibly emit it only * when they have a fix, so watching for it can make them look * like they have a variable fix reporting cycle. */
year = atoi(field[4]);
mon = atoi(field[3]);
mday = atoi(field[2]);
century = year - year % 100;
if ( (1900 > year ) || (2200 < year ) ) {
gpsd_log(&session->context->errout, LOG_WARN,
"malformed ZDA year: %s\n", field[4]);
} else if ( (1 > mon ) || (12 < mon ) ) {
gpsd_log(&session->context->errout, LOG_WARN,
"malformed ZDA month: %s\n", field[3]);
} else if ( (1 > mday ) || (31 < mday ) ) {
gpsd_log(&session->context->errout, LOG_WARN,
"malformed ZDA day: %s\n", field[2]);
} else {
gpsd_century_update(session, century);
session->nmea.date.tm_year = year - 1900;
session->nmea.date.tm_mon = mon - 1;
session->nmea.date.tm_mday = mday;
mask = TIME_SET;
}
};
return mask;
}
static gps_mask_t processHDT(int c UNUSED, char *field[],
struct gps_device_t *session)
{
/* * $HEHDT,341.8,T*21 * * HDT,x.x*hh<cr><lf> * * The only data field is true heading in degrees. * The following field is required to be 'T' indicating a true heading. * It is followed by a mandatory nmea_checksum. */
gps_mask_t mask;
mask = ONLINE_SET;
session->gpsdata.attitude.heading = safe_atof(field[1]);
session->gpsdata.attitude.mag_st = '\0';
session->gpsdata.attitude.pitch = NAN;
session->gpsdata.attitude.pitch_st = '\0';
session->gpsdata.attitude.roll = NAN;
session->gpsdata.attitude.roll_st = '\0';
session->gpsdata.attitude.yaw = NAN;
session->gpsdata.attitude.yaw_st = '\0';
session->gpsdata.attitude.dip = NAN;
session->gpsdata.attitude.mag_len = NAN;
session->gpsdata.attitude.mag_x = NAN;
session->gpsdata.attitude.mag_y = NAN;
session->gpsdata.attitude.mag_z = NAN;
session->gpsdata.attitude.acc_len = NAN;
session->gpsdata.attitude.acc_x = NAN;
session->gpsdata.attitude.acc_y = NAN;
session->gpsdata.attitude.acc_z = NAN;
session->gpsdata.attitude.gyro_x = NAN;
session->gpsdata.attitude.gyro_y = NAN;
session->gpsdata.attitude.temp = NAN;
session->gpsdata.attitude.depth = NAN;
mask |= (ATTITUDE_SET);
gpsd_log(&session->context->errout, LOG_RAW,
"time %.3f, heading %lf.\n",
session->newdata.time,
session->gpsdata.attitude.heading);
return mask;
}
static gps_mask_t processDBT(int c UNUSED, char *field[],
struct gps_device_t *session)
{
/* * $SDDBT,7.7,f,2.3,M,1.3,F*05 * 1) Depth below sounder in feet * 2) Fixed value 'f' indicating feet * 3) Depth below sounder in meters * 4) Fixed value 'M' indicating meters * 5) Depth below sounder in fathoms * 6) Fixed value 'F' indicating fathoms * 7) Checksum. * * In real-world sensors, sometimes not all three conversions are reported. */
gps_mask_t mask;
mask = ONLINE_SET;
if (field[3][0] != '\0') {
session->newdata.altitude = -safe_atof(field[3]);
mask |= (ALTITUDE_SET);
} else if (field[1][0] != '\0') {
session->newdata.altitude = -safe_atof(field[1]) / METERS_TO_FEET;
mask |= (ALTITUDE_SET);
} else if (field[5][0] != '\0') {
session->newdata.altitude = -safe_atof(field[5]) / METERS_TO_FATHOMS;
mask |= (ALTITUDE_SET);
}
if ((mask & ALTITUDE_SET) != 0) {
if (session->newdata.mode < MODE_3D) {
session->newdata.mode = MODE_3D;
mask |= MODE_SET;
}
}
/* * Hack: We report depth below keep as negative altitude because there's * no better place to put it. Should work in practice as nobody is * likely to be operating a depth sounder at varying altitudes. */
gpsd_log(&session->context->errout, LOG_RAW,
"mode %d, depth %lf.\n",
session->newdata.mode,
session->newdata.altitude);
return mask;
}
static gps_mask_t processTXT(int count, char *field[],
struct gps_device_t *session)
/* GPS Text message */
{
/* * $GNTXT,01,01,01,PGRM inv format*2A * 1 Number of sentences for full data * 1 Sentence 1 of 1 * 01 Message type * 00 - error * 01 - warning * 02 - notice * 07 - user * PGRM inv format ASCII text * * Can occur with talker IDs: * BD (Beidou), * GA (Galileo), * GB (Beidou), * GL (GLONASS), * GN (GLONASS, any combination GNSS), * GP (GPS, SBAS, QZSS), * QZ (QZSS). */
gps_mask_t mask = 0;
int msgType = 0;
char *msgType_txt = "Unknown";
if ( 5 != count) {
return 0;
}
/* set something, so it won't look like an unknown sentence */
mask |= ONLINE_SET;
msgType = atoi(field[3]);
switch ( msgType ) {
case 0:
msgType_txt = "Error";
break;
case 1:
msgType_txt = "Warning";
break;
case 2:
msgType_txt = "Notice";
break;
case 7:
msgType_txt = "User";
break;
}
/* maximum text lenght unknown, guess 80 */
gpsd_log(&session->context->errout, LOG_WARN,
"TXT: %.10s: %.80s\n",
msgType_txt, field[4]);
return mask;
}
#ifdef TNT_ENABLE
static gps_mask_t processTNTHTM(int c UNUSED, char *field[],
struct gps_device_t *session)
{
/* * Proprietary sentence for True North Technologies Magnetic Compass. * This may also apply to some Honeywell units since they may have been * designed by True North. $PTNTHTM,14223,N,169,N,-43,N,13641,2454*15 HTM,x.x,a,x.x,a,x.x,a,x.x,x.x*hh<cr><lf> Fields in order: 1. True heading (compass measurement + deviation + variation) 2. magnetometer status character: C = magnetometer calibration alarm L = low alarm M = low warning N = normal O = high warning P = high alarm V = magnetometer voltage level alarm 3. pitch angle 4. pitch status character - see field 2 above 5. roll angle 6. roll status character - see field 2 above 7. dip angle 8. relative magnitude horizontal component of earth's magnetic field *hh mandatory nmea_checksum By default, angles are reported as 26-bit integers: weirdly, the technical manual says either 0 to 65535 or -32768 to 32767 can occur as a range. */
gps_mask_t mask;
mask = ONLINE_SET;
session->gpsdata.attitude.heading = safe_atof(field[1]);
session->gpsdata.attitude.mag_st = *field[2];
session->gpsdata.attitude.pitch = safe_atof(field[3]);
session->gpsdata.attitude.pitch_st = *field[4];
session->gpsdata.attitude.roll = safe_atof(field[5]);
session->gpsdata.attitude.roll_st = *field[6];
session->gpsdata.attitude.yaw = NAN;
session->gpsdata.attitude.yaw_st = '\0';
session->gpsdata.attitude.dip = safe_atof(field[7]);
session->gpsdata.attitude.mag_len = NAN;
session->gpsdata.attitude.mag_x = safe_atof(field[8]);
session->gpsdata.attitude.mag_y = NAN;
session->gpsdata.attitude.mag_z = NAN;
session->gpsdata.attitude.acc_len = NAN;
session->gpsdata.attitude.acc_x = NAN;
session->gpsdata.attitude.acc_y = NAN;
session->gpsdata.attitude.acc_z = NAN;
session->gpsdata.attitude.gyro_x = NAN;
session->gpsdata.attitude.gyro_y = NAN;
session->gpsdata.attitude.temp = NAN;
session->gpsdata.attitude.depth = NAN;
mask |= (ATTITUDE_SET);
gpsd_log(&session->context->errout, LOG_RAW,
"time %.3f, heading %lf (%c).\n",
session->newdata.time,
session->gpsdata.attitude.heading,
session->gpsdata.attitude.mag_st);
return mask;
}
#endif /* TNT_ENABLE */
#ifdef OCEANSERVER_ENABLE
static gps_mask_t processOHPR(int c UNUSED, char *field[],
struct gps_device_t *session)
{
/* * Proprietary sentence for OceanServer Magnetic Compass. OHPR,x.x,x.x,x.x,x.x,x.x,x.x,x.x,x.x,x.x,x.x,x.x,x.x,x.x,x.x,x.x,x.x,x.x,x.x*hh<cr><lf> Fields in order: 1. Azimuth 2. Pitch Angle 3. Roll Angle 4. Sensor temp, degrees centigrade 5. Depth (feet) 6. Magnetic Vector Length 7-9. 3 axis Magnetic Field readings x,y,z 10. Acceleration Vector Length 11-13. 3 axis Acceleration Readings x,y,z 14. Reserved 15-16. 2 axis Gyro Output, X,y 17. Reserved 18. Reserved *hh mandatory nmea_checksum */
gps_mask_t mask;
mask = ONLINE_SET;
session->gpsdata.attitude.heading = safe_atof(field[1]);
session->gpsdata.attitude.mag_st = '\0';
session->gpsdata.attitude.pitch = safe_atof(field[2]);
session->gpsdata.attitude.pitch_st = '\0';
session->gpsdata.attitude.roll = safe_atof(field[3]);
session->gpsdata.attitude.roll_st = '\0';
session->gpsdata.attitude.yaw = NAN;
session->gpsdata.attitude.yaw_st = '\0';
session->gpsdata.attitude.dip = NAN;
session->gpsdata.attitude.temp = safe_atof(field[4]);
session->gpsdata.attitude.depth = safe_atof(field[5]) / METERS_TO_FEET;
session->gpsdata.attitude.mag_len = safe_atof(field[6]);
session->gpsdata.attitude.mag_x = safe_atof(field[7]);
session->gpsdata.attitude.mag_y = safe_atof(field[8]);
session->gpsdata.attitude.mag_z = safe_atof(field[9]);
session->gpsdata.attitude.acc_len = safe_atof(field[10]);
session->gpsdata.attitude.acc_x = safe_atof(field[11]);
session->gpsdata.attitude.acc_y = safe_atof(field[12]);
session->gpsdata.attitude.acc_z = safe_atof(field[13]);
session->gpsdata.attitude.gyro_x = safe_atof(field[15]);
session->gpsdata.attitude.gyro_y = safe_atof(field[16]);
mask |= (ATTITUDE_SET);
gpsd_log(&session->context->errout, LOG_RAW,
"Heading %lf.\n", session->gpsdata.attitude.heading);
return mask;
}
#endif /* OCEANSERVER_ENABLE */
#ifdef ASHTECH_ENABLE
/* Ashtech sentences take this format: * $PASHDR,type[,val[,val]]*CS * type is an alphabetic subsentence type * * Oxford Technical Solutions (OXTS) also uses the $PASHR sentence, * but with a very different sentence contents: * $PASHR,HHMMSS.SSS,HHH.HH,T,RRR.RR,PPP.PP,aaa.aa,r.rrr,p.ppp,h.hhh,Q1,Q2*CS * * so field 1 in ASHTECH is always alphabetic and numeric in OXTS * FIXME: decode OXTS $PASHDR * */
static gps_mask_t processPASHR(int c UNUSED, char *field[],
struct gps_device_t *session)
{
gps_mask_t mask;
mask = 0;
if (0 == strcmp("RID", field[1])) {
/* Receiver ID */
(void)snprintf(session->subtype, sizeof(session->subtype) - 1,
"%s ver %s", field[2], field[3]);
gpsd_log(&session->context->errout, LOG_DATA,
"PASHR,RID: subtype=%s mask={}\n",
session->subtype);
return mask;
} else if (0 == strcmp("POS", field[1])) {
/* 3D Position */
mask |= MODE_SET | STATUS_SET | CLEAR_IS;
if (0 == strlen(field[2])) {
/* empty first field means no 3D fix is available */
session->gpsdata.status = STATUS_NO_FIX;
session->newdata.mode = MODE_NO_FIX;
} else {
/* if we make it this far, we at least have a 3D fix */
session->newdata.mode = MODE_3D;
if (1 == atoi(field[2]))
session->gpsdata.status = STATUS_DGPS_FIX;
else
session->gpsdata.status = STATUS_FIX;
session->gpsdata.satellites_used = atoi(field[3]);
merge_hhmmss(field[4], session);
register_fractional_time(field[0], field[4], session);
do_lat_lon(&field[5], &session->newdata);
session->newdata.altitude = safe_atof(field[9]);
session->newdata.track = safe_atof(field[11]);
session->newdata.speed = safe_atof(field[12]) / MPS_TO_KPH;
session->newdata.climb = safe_atof(field[13]);
session->gpsdata.dop.pdop = safe_atof(field[14]);
session->gpsdata.dop.hdop = safe_atof(field[15]);
session->gpsdata.dop.vdop = safe_atof(field[16]);
session->gpsdata.dop.tdop = safe_atof(field[17]);
mask |= (TIME_SET | LATLON_SET | ALTITUDE_SET);
mask |= (SPEED_SET | TRACK_SET | CLIMB_SET);
mask |= DOP_SET;
gpsd_log(&session->context->errout, LOG_DATA,
"PASHR,POS: hhmmss=%s lat=%.2f lon=%.2f alt=%.f speed=%.2f track=%.2f climb=%.2f mode=%d status=%d pdop=%.2f hdop=%.2f vdop=%.2f tdop=%.2f\n",
field[4], session->newdata.latitude,
session->newdata.longitude, session->newdata.altitude,
session->newdata.speed, session->newdata.track,
session->newdata.climb, session->newdata.mode,
session->gpsdata.status, session->gpsdata.dop.pdop,
session->gpsdata.dop.hdop, session->gpsdata.dop.vdop,
session->gpsdata.dop.tdop);
}
} else if (0 == strcmp("SAT", field[1])) {
/* Satellite Status */
struct satellite_t *sp;
int i, n = session->gpsdata.satellites_visible = atoi(field[2]);
session->gpsdata.satellites_used = 0;
for (i = 0, sp = session->gpsdata.skyview; sp < session->gpsdata.skyview + n; sp++, i++) {
sp->PRN = (short)atoi(field[3 + i * 5 + 0]);
sp->azimuth = (short)atoi(field[3 + i * 5 + 1]);
sp->elevation = (short)atoi(field[3 + i * 5 + 2]);
sp->ss = safe_atof(field[3 + i * 5 + 3]);
sp->used = false;
if (field[3 + i * 5 + 4][0] == 'U') {
sp->used = true;
session->gpsdata.satellites_used++;
}
}
gpsd_log(&session->context->errout, LOG_DATA,
"PASHR,SAT: used=%d\n",
session->gpsdata.satellites_used);
session->gpsdata.skyview_time = NAN;
mask |= SATELLITE_SET | USED_IS;
}
return mask;
}
#endif /* ASHTECH_ENABLE */
#ifdef MTK3301_ENABLE
static gps_mask_t processMTK3301(int c UNUSED, char *field[],
struct gps_device_t *session)
{
int msg, reason;
msg = atoi(&(session->nmea.field[0])[4]);
switch (msg) {
case 001: /* ACK / NACK */
reason = atoi(field[2]);
if (atoi(field[1]) == -1)
gpsd_log(&session->context->errout, LOG_WARN,
"MTK NACK: unknown sentence\n");
else if (reason < 3) {
const char *mtk_reasons[] = {
"Invalid",
"Unsupported",
"Valid but Failed",
"Valid success"
};
gpsd_log(&session->context->errout, LOG_WARN,
"MTK NACK: %s, reason: %s\n",
field[1], mtk_reasons[reason]);
}
else
gpsd_log(&session->context->errout, LOG_DATA,
"MTK ACK: %s\n", field[1]);
return ONLINE_SET;
case 424: /* PPS pulse width response */
/* * Response will look something like: $PMTK424,0,0,1,0,69*12 * The pulse width is in field 5 (69 in this example). This * sentence is poorly documented at: * http://www.trimble.com/embeddedsystems/condor-gps-module.aspx?dtID=documentation * * Packet Type: 324 PMTK_API_SET_OUTPUT_CTL * Packet meaning * Write the TSIP / antenna / PPS configuration data to the Flash memory. * DataField [Data0]:TSIP Packet[on/off] * 0 - Disable TSIP output (Default). * 1 - Enable TSIP output. * [Data1]:Antenna Detect[on/off] * 0 - Disable antenna detect function (Default). * 1 - Enable antenna detect function. * [Data2]:PPS on/off * 0 - Disable PPS function. * 1 - Enable PPS function (Default). * [Data3]:PPS output timing * 0 - Always output PPS (Default). * 1 - Only output PPS when GPS position is fixed. * [Data4]:PPS pulse width * 1~16367999: 61 ns~(61x 16367999) ns (Default = 69) * * The documentation does not give the units of the data field. * Andy Walls <[email protected]> says: * * "The best I can figure using an oscilloscope, is that it is * in units of 16.368000 MHz clock cycles. It may be * different for any other unit other than the Trimble * Condor. 69 cycles / 16368000 cycles/sec = 4.216 microseconds * [which is the pulse width I have observed]" * * Support for this theory comes from the fact that crystal * TXCOs with a 16.368MHZ period are commonly available from * multiple vendors. Furthermore, 61*69 = 4209, which is * close to the observed cycle time and suggests that the * documentation is trying to indicate 61ns units. * * He continues: * * "I chose [127875] because to divides 16368000 nicely and the * pulse width is close to 1/100th of a second. Any number * the user wants to use would be fine. 127875 cycles / * 16368000 cycles/second = 1/128 seconds = 7.8125 * milliseconds" */
/* too short? Make it longer */
if (atoi(field[5]) < 127875)
(void)nmea_send(session, "$PMTK324,0,0,1,0,127875");
return ONLINE_SET;
case 705: /* return device subtype */
(void)strlcat(session->subtype, field[1], sizeof(session->subtype));
(void)strlcat(session->subtype, "-", sizeof(session->subtype));
(void)strlcat(session->subtype, field[2], sizeof(session->subtype));
return ONLINE_SET;
default:
gpsd_log(&session->context->errout, LOG_PROG,
"MTK: unknown msg: %d\n", msg);
return ONLINE_SET; /* ignore */
}
}
#endif /* MTK3301_ENABLE */
/************************************************************************** * * Entry points begin here * **************************************************************************/
gps_mask_t nmea_parse(char *sentence, struct gps_device_t * session)
/* parse an NMEA sentence, unpack it into a session structure */
{
typedef gps_mask_t(*nmea_decoder) (int count, char *f[],
struct gps_device_t * session);
static struct
{
char *name;
int nf; /* minimum number of fields required to parse */
bool cycle_continue; /* cycle continuer? */
nmea_decoder decoder;
} nmea_phrase[] = {
{
"PGRMC", 0, false, NULL}, /* ignore Garmin Sensor Config */
{
"PGRME", 7, false, processPGRME},
{
"PGRMI", 0, false, NULL}, /* ignore Garmin Sensor Init */
{
"PGRMO", 0, false, NULL}, /* ignore Garmin Sentence Enable */
/* * Basic sentences must come after the PG* ones, otherwise * Garmins can get stuck in a loop that looks like this: * * 1. A Garmin GPS in NMEA mode is detected. * * 2. PGRMC is sent to reconfigure to Garmin binary mode. * If successful, the GPS echoes the phrase. * * 3. nmea_parse() sees the echo as RMC because the talker * ID is ignored, and fails to recognize the echo as * PGRMC and ignore it. * * 4. The mode is changed back to NMEA, resulting in an * infinite loop. */
{
"DBT", 7, true, processDBT},
{
"GBS", 7, false, processGBS},
{
"GGA", 13, false, processGGA},
{
"GLL", 7, false, processGLL},
{
"GSA", 17, false, processGSA},
{
"GST", 8, false, processGST},
{
"GSV", 0, false, processGSV},
{
"HDT", 1, false, processHDT},
#ifdef OCEANSERVER_ENABLE
{
"OHPR", 18, false, processOHPR},
#endif /* OCEANSERVER_ENABLE */
#ifdef ASHTECH_ENABLE
{
"PASHR", 3, false, processPASHR}, /* general handler for Ashtech */
#endif /* ASHTECH_ENABLE */
#ifdef MTK3301_ENABLE
{
"PMTK", 3, false, processMTK3301},
/* for some reason thhe parser no longer triggering on leading chars */
{
"PMTK001", 3, false, processMTK3301},
{
"PMTK424", 3, false, processMTK3301},
{
"PMTK705", 3, false, processMTK3301},
#endif /* MTK3301_ENABLE */
#ifdef TNT_ENABLE
{
"PTNTHTM", 9, false, processTNTHTM},
#endif /* TNT_ENABLE */
{
"RMC", 8, false, processRMC},
{
"TXT", 5, false, processTXT},
{
"ZDA", 4, false, processZDA},
{
"VTG", 0, false, NULL}, /* ignore Velocity Track made Good */
};
int count;
gps_mask_t retval = 0;
unsigned int i, thistag;
char *p, *s, *e;
volatile char *t;
/* * We've had reports that on the Garmin GPS-10 the device sometimes * (1:1000 or so) sends garbage packets that have a valid checksum * but are like 2 successive NMEA packets merged together in one * with some fields lost. Usually these are much longer than the * legal limit for NMEA, so we can cope by just tossing out overlong * packets. This may be a generic bug of all Garmin chipsets. */
if (strlen(sentence) > NMEA_MAX) {
gpsd_log(&session->context->errout, LOG_WARN,
"Overlong packet of %zd chars rejected.\n",
strlen(sentence));
return ONLINE_SET;
}
/* make an editable copy of the sentence */
(void)strlcpy((char *)session->nmea.fieldcopy, sentence, sizeof(session->nmea.fieldcopy) - 1);
/* discard the checksum part */
for (p = (char *)session->nmea.fieldcopy;
(*p != '*') && (*p >= ' ');)
++p;
if (*p == '*')
*p++ = ','; /* otherwise we drop the last field */
*p = '\0';
e = p;
/* split sentence copy on commas, filling the field array */
count = 0;
t = p; /* end of sentence */
p = (char *)session->nmea.fieldcopy + 1; /* beginning of tag, 'G' not '$' */
/* while there is a search string and we haven't run off the buffer... */
while ((p != NULL) && (p <= t)) {
session->nmea.field[count] = p; /* we have a field. record it */
if ((p = strchr(p, ',')) != NULL) {
/* search for the next delimiter */
*p = '\0'; /* replace it with a NUL */
count++; /* bump the counters and continue */
p++;
}
}
/* point remaining fields at empty string, just in case */
for (i = (unsigned int)count;
i <
(unsigned)(sizeof(session->nmea.field) /
sizeof(session->nmea.field[0])); i++)
session->nmea.field[i] = e;
/* sentences handlers will tell us when they have fractional time */
session->nmea.latch_frac_time = false;
/* dispatch on field zero, the sentence tag */
for (thistag = i = 0;
i < (unsigned)(sizeof(nmea_phrase) / sizeof(nmea_phrase[0])); ++i) {
s = session->nmea.field[0];
if (strlen(nmea_phrase[i].name) == 3)
s += 2; /* skip talker ID */
if (strcmp(nmea_phrase[i].name, s) == 0) {
if (nmea_phrase[i].decoder != NULL
&& (count >= nmea_phrase[i].nf)) {
retval =
(nmea_phrase[i].decoder) (count,
session->nmea.field,
session);
if (nmea_phrase[i].cycle_continue)
session->nmea.cycle_continue = true;
/* * Must force this to be nz, as we're going to rely on a zero * value to mean "no previous tag" later. */
thistag = i + 1;
} else
retval = ONLINE_SET; /* unknown sentence */
break;
}
}
/* prevent overaccumulation of sat reports */
if (!str_starts_with(session->nmea.field[0] + 2, "GSV"))
session->nmea.last_gsv_talker = '\0';
/* timestamp recording for fixes happens here */
if ((retval & TIME_SET) != 0) {
session->newdata.time = gpsd_utc_resolve(session);
/* * WARNING: This assumes time is always field 0, and that field 0 * is a timestamp whenever TIME_SET is set. */
gpsd_log(&session->context->errout, LOG_DATA,
"%s time is %2f = %d-%02d-%02dT%02d:%02d:%02.2fZ\n",
session->nmea.field[0], session->newdata.time,
1900 + session->nmea.date.tm_year,
session->nmea.date.tm_mon + 1,
session->nmea.date.tm_mday,
session->nmea.date.tm_hour,
session->nmea.date.tm_min,
session->nmea.date.tm_sec + session->nmea.subseconds);
/* * If we have time and PPS is available, assume we have good time. * Because this is a generic driver we don't really have enough * information for a sharper test, so we'll leave it up to the * PPS code to do its own sanity filtering. */
retval |= PPSTIME_IS;
}
/* * The end-of-cycle detector. This code depends on just one * assumption: if a sentence with a timestamp occurs just before * start of cycle, then it is always good to trigger a report on * that sentence in the future. For devices with a fixed cycle * this should work perfectly, locking in detection after one * cycle. Most split-cycle devices (Garmin 48, for example) will * work fine. Problems will only arise if a a sentence that * occurs just befiore timestamp increments also occurs in * mid-cycle, as in the Garmin eXplorist 210; those might jitter. */
if (session->nmea.latch_frac_time) {
gpsd_log(&session->context->errout, LOG_PROG,
"%s sentence timestamped %.2f.\n",
session->nmea.field[0],
session->nmea.this_frac_time);
if (!GPS_TIME_EQUAL
(session->nmea.this_frac_time,
session->nmea.last_frac_time)) {
uint lasttag = session->nmea.lasttag;
retval |= CLEAR_IS;
gpsd_log(&session->context->errout, LOG_PROG,
"%s starts a reporting cycle.\n",
session->nmea.field[0]);
/* * Have we seen a previously timestamped NMEA tag? * If so, designate as end-of-cycle marker. * But not if there are continuation sentences; * those get sorted after the last timestamped sentence */
if (lasttag > 0
&& (session->nmea.cycle_enders & (1 << lasttag)) == 0
&& !session->nmea.cycle_continue) {
session->nmea.cycle_enders |= (1 << lasttag);
gpsd_log(&session->context->errout, LOG_PROG,
"tagged %s as a cycle ender.\n",
nmea_phrase[lasttag - 1].name);
}
}
} else {
/* extend the cycle to an un-timestamped sentence? */
if ((session->nmea.lasttag & session->nmea.cycle_enders) != 0)
gpsd_log(&session->context->errout, LOG_PROG,
"%s is just after a cycle ender.\n",
session->nmea.field[0]);
if (session->nmea.cycle_continue) {
gpsd_log(&session->context->errout, LOG_PROG,
"%s extends the reporting cycle.\n",
session->nmea.field[0]);
session->nmea.cycle_enders &=~ (1 << session->nmea.lasttag);
session->nmea.cycle_enders |= (1 << thistag);
}
}
/* here's where we check for end-of-cycle */
if ((session->nmea.latch_frac_time || session->nmea.cycle_continue)
&& (session->nmea.cycle_enders & (1 << thistag))!=0) {
gpsd_log(&session->context->errout, LOG_PROG,
"%s ends a reporting cycle.\n",
session->nmea.field[0]);
retval |= REPORT_IS;
}
if (session->nmea.latch_frac_time)
session->nmea.lasttag = thistag;
/* we might have a reliable end-of-cycle */
if (session->nmea.cycle_enders != 0)
session->cycle_end_reliable = true;
return retval;
}
#endif /* NMEA0183_ENABLE */
void nmea_add_checksum(char *sentence)
/* add NMEA checksum to a possibly *-terminated sentence */
{
unsigned char sum = '\0';
char c, *p = sentence;
if (*p == '$' || *p == '!') {
p++;
}
while (((c = *p) != '*') && (c != '\0')) {
sum ^= c;
p++;
}
*p++ = '*';
(void)snprintf(p, 5, "%02X\r\n", (unsigned)sum);
}
ssize_t nmea_write(struct gps_device_t *session, char *buf, size_t len UNUSED)
/* ship a command to the GPS, adding * and correct checksum */
{
(void)strlcpy(session->msgbuf, buf, sizeof(session->msgbuf));
if (session->msgbuf[0] == '$') {
(void)strlcat(session->msgbuf, "*", sizeof(session->msgbuf));
nmea_add_checksum(session->msgbuf);
} else
(void)strlcat(session->msgbuf, "\r\n", sizeof(session->msgbuf));
session->msgbuflen = strlen(session->msgbuf);
return gpsd_write(session, session->msgbuf, session->msgbuflen);
}
ssize_t nmea_send(struct gps_device_t * session, const char *fmt, ...)
{
char buf[BUFSIZ];
va_list ap;
va_start(ap, fmt);
(void)vsnprintf(buf, sizeof(buf) - 5, fmt, ap);
va_end(ap);
return nmea_write(session, buf, strlen(buf));
}
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