ControlForge NMEA & GPS Guide

James M. Belcher Founder, JMB Technical Services LLC April 2026 | ControlForge v1.0.535

1. Overview

26 built-in functions for GPS/GNSS integration from Structured Text. Parse NMEA sentences from serial GPS receivers, extract position/speed/altitude, and perform geospatial calculations — geofencing, distance, bearing, and coordinate conversion.

2. NMEA Sentence Parsing (17)

(* Parse a GPRMC sentence from serial GPS *)
sentence := '$GPRMC,123519,A,4807.038,N,01131.000,E,022.4,084.4,230394,003.1,W*6A';
nmea := NMEA_PARSE(sentence);

IF NMEA_VALID(nmea) THEN
    msg_type := NMEA_GET_TYPE(nmea);        (* "GPRMC" *)
    lat := NMEA_GET_LAT(nmea);              (* 48.1173 decimal degrees *)
    lon := NMEA_GET_LON(nmea);              (* 11.5167 decimal degrees *)
    speed := NMEA_GET_SPEED(nmea);          (* m/s *)
    course := NMEA_GET_COURSE(nmea);        (* degrees *)
    date := NMEA_GET_DATE(nmea);            (* "1994-03-23" *)
    time := NMEA_GET_TIME(nmea);            (* "12:35:19" *)
END_IF;

(* GGA sentence — altitude and fix quality *)
gga := NMEA_PARSE('$GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,47.0,M,,*47');
alt := NMEA_GET_ALT(gga);                  (* 545.4 meters *)
fix := NMEA_GET_FIX(gga);                  (* 1 = GPS fix *)
sats := NMEA_GET_SATS(gga);               (* 8 satellites *)
hdop := NMEA_GET_HDOP(gga);               (* 0.9 *)

(* Raw field access *)
field_count := NMEA_FIELD_COUNT(nmea);
raw_field := NMEA_GET_FIELD(nmea, 3);      (* Field by index *)

(* Build and validate *)
checksum := NMEA_CHECKSUM('GPRMC,123519,A,...');
custom := NMEA_BUILD('PPLC', 'ControlForge', '1.0', '72.5');
(* Returns: "$PPLC,ControlForge,1.0,72.5*XX" with calculated checksum *)

Function	Parameters	Returns	Description
`NMEA_PARSE(sentence)`	1	Handle	Parse NMEA sentence
`NMEA_VALID(h)`	1	BOOL	Verify checksum
`NMEA_GET_TYPE(h)`	1	STRING	Sentence type ("GPRMC", "GPGGA")
`NMEA_GET_LAT(h)`	1	REAL	Latitude (decimal degrees)
`NMEA_GET_LON(h)`	1	REAL	Longitude (decimal degrees)
`NMEA_GET_ALT(h)`	1	REAL	Altitude (meters, GGA only)
`NMEA_GET_SPEED(h)`	1	REAL	Speed (m/s)
`NMEA_GET_COURSE(h)`	1	REAL	Course (degrees)
`NMEA_GET_DATE(h)`	1	STRING	Date (YYYY-MM-DD)
`NMEA_GET_TIME(h)`	1	STRING	Time (HH:MM:SS)
`NMEA_GET_FIX(h)`	1	INT	Fix quality (0=none, 1=GPS, 2=DGPS)
`NMEA_GET_SATS(h)`	1	INT	Satellite count
`NMEA_GET_HDOP(h)`	1	REAL	Horizontal dilution of precision
`NMEA_GET_FIELD(h, index)`	2	STRING	Raw field by index
`NMEA_FIELD_COUNT(h)`	1	INT	Total fields
`NMEA_CHECKSUM(str)`	1	STRING	Calculate 2-char hex checksum
`NMEA_BUILD(type, fields...)`	2+	STRING	Build sentence with checksum

3. GPS Calculations (9)

Geodesic functions using the haversine formula.

(* Distance between two points *)
dist := GPS_DISTANCE(48.1173, 11.5167, 48.1375, 11.5755);    (* meters *)

(* Bearing from point A to point B *)
bearing := GPS_BEARING(48.1173, 11.5167, 48.1375, 11.5755);  (* degrees 0-360 *)

(* Calculate destination from start + bearing + distance *)
dest := GPS_DESTINATION(48.1173, 11.5167, 45.0, 1000.0);     (* 1km NE *)
new_lat := JSON_GET_REAL(dest, 'lat');
new_lon := JSON_GET_REAL(dest, 'lon');

(* Midpoint *)
mid := GPS_MIDPOINT(48.1173, 11.5167, 48.1375, 11.5755);

(* Speed from two positions + time *)
speed := GPS_SPEED(lat1, lon1, lat2, lon2, elapsed_seconds);  (* m/s *)

(* Geofencing *)
in_zone := GPS_IN_RADIUS(lat, lon, center_lat, center_lon, 500.0);  (* 500m radius *)
in_area := GPS_IN_RECT(lat, lon, min_lat, min_lon, max_lat, max_lon);

(* Coordinate conversion *)
dms := GPS_DD_TO_DMS(48.1173, 'N');    (* {deg:48, min:7, sec:2.28, dir:"N"} *)
dd := GPS_DMS_TO_DD(48, 7, 2.28, 'N'); (* 48.1173 *)

Function	Parameters	Returns	Description
`GPS_DISTANCE(lat1,lon1,lat2,lon2)`	4	REAL	Distance in meters (haversine)
`GPS_BEARING(lat1,lon1,lat2,lon2)`	4	REAL	Bearing in degrees (0-360)
`GPS_DESTINATION(lat,lon,bearing,dist)`	4	MAP	Destination {lat, lon}
`GPS_MIDPOINT(lat1,lon1,lat2,lon2)`	4	MAP	Midpoint {lat, lon}
`GPS_SPEED(lat1,lon1,lat2,lon2,sec)`	5	REAL	Speed in m/s
`GPS_IN_RADIUS(lat,lon,clat,clon,r)`	5	BOOL	Within radius?
`GPS_IN_RECT(lat,lon,minlat,minlon,maxlat,maxlon)`	6	BOOL	Within rectangle?
`GPS_DD_TO_DMS(dd [,axis])`	1-2	MAP	Decimal → degrees/minutes/seconds
`GPS_DMS_TO_DD(deg,min,sec [,dir])`	3-4	REAL	DMS → decimal degrees

ControlForge v1.0.535 | 26 NMEA/GPS Functions | GPS Parsing, Geofencing, Geodesic Math

1. Overview​

2. NMEA Sentence Parsing (17)​

3. GPS Calculations (9)​

1. Overview

2. NMEA Sentence Parsing (17)

3. GPS Calculations (9)