GPS lib

Library to interface with GPS devices. More specifically parses NMEA and UBX messages.

Features

Reads from serial interface data from a GPS device. Then matches the data with the known messages (NMEA and UBX), then it parses the data and eventually saves the parsed values in corresponding CSV files.

Parsed messages

NMEA

• GGA
• GSA
• VTG

UBX

• NAV-DOP
• NAV-PVT
• NAV-HPPOSECEF
• HPPOSLLH

Usage

Reading from GPS

Use gps_interface.h to access to utils functions to read data from the connected GPS.

int gps_interface_open(
    gps_serial_port* new_serial_port,
    const char* port,
    speed_t speed
);

gps_protocol_type gps_interface_get_line(
    gps_serial_port* port,
    char start_sequence[GPS_MAX_START_SEQUENCE_SIZE],
    int* start_sequence_size,
    char line[GPS_MAX_LINE_SIZE],
    int* line_size
);

• gps_interface_open: is to open a serialport given the device name (ex: /dev/ttyACM0) and given speed.
• gps_interface_get_line: reads a line from the device returning the protocol of the line, the start sequence and the actual line.

gps_protocol_type protocol_type = gps_interface_get_line(&port, start_sequence, &start_sequence_bytes, line, &line_bytes);
if(protocol_type == GPS_PROTOCOL_TYPE_SIZE){
    cout << "error reading gps" << endl;
}else{
    // All ok, do stuff
}

Setting protocol_type to max, is used to notify that an error occurred reading the port.

Parsing GPS data

To parse GPS data use functions and structures in gps.h.

Define the data struct:

gps_parsed_data_t data;

To parse data fist must be detected the message type, then if it is a velid type the parsing can take place:

gps_protocol_and_message match;
if(gps_match_message(&match, line, protocol_type) == -1){
    printf("Protocol: %d, match failed", match.protocol); // it fails if the message is not supported from this lib
    continue;
}

gps_parse_result_t result = gps_parse_buffer(&parsed_gps, &match, line, timestamp);
if(result == GPS_PARSE_RESULT_OK){
    // Do stuff
}else{
    printf("Protocol %d. Message %d. Parse failed with error: %s", match.protocol, match.message, gps_parse_result_string[result]);
}

Saving GPS data

The first thing is to open GPS files:

const char* path = "/path/to/folder/";
gps_files_t gps_files;              // struct containing gps files
gps_open_files(&gps_files, path);   // open one csv file per message
gps_header_to_file(&gps_files);     // write csv headers
FILE* raw_log = fopen((std::string(path) + "gps.log").c_str(), "w");        // to log raw data from gps

To save raw data from the GPS:

for(int i = 0; i < start_sequence_bytes; i++)
    fprintf(raw_log, "%c", start_sequence[i]);
for(int i = 0; i < line_bytes; i++)
    fprintf(raw_log, "%c", line[i]);
fprintf(raw_log, "\n");

To save also the parsed data in a CSV file:

if(result == GPS_PARSE_RESULT_OK){  // only if parsing was successfull
    gps_to_file(&gps_files, &parsed_gps, &match);
}