nmea.cpp

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/*
 * nmea.cpp
 *
 *  Created on: 29 jul. 2024
 *      Author: jancu
 */
 
module;
 
#include <cassert>
#include <ranges>
#include <cmath>
#include <chrono>
 
module nmea;
 
using std::operator""sv;
constexpr auto delim{","sv};
 
namespace nmea {
 
talker_id nmea::talker(const std::string_view& sv) {
    talker_id id = talker_id::gps;
    if (sv.starts_with("$GP")) {
        id = talker_id::gps;
    } else if (sv.starts_with("$GL")) {
        id = talker_id::glonass;
    } else if (sv.starts_with("$GA")) {
        id = talker_id::galileo;
    } else if (sv.starts_with("$BD")) {
        id = talker_id::beidou;
    } else if (sv.starts_with("$QZ")) {
        id = talker_id::qzss;
    } else if (sv.starts_with("$GN")) {
        id = talker_id::multiconstellation;
    }
    return id;
}
 
talker_id nmea::system(const std::string_view& sv) {
    talker_id id = talker_id::gps;
    if (sv.starts_with("1")) {
        id = talker_id::gps;
    } else if (sv.starts_with("2")) {
        id = talker_id::glonass;
    } else if (sv.starts_with("3")) {
        id = talker_id::galileo;
    } else if (sv.starts_with("4")) {
        id = talker_id::beidou;
    } else if (sv.starts_with("5")) {
        id = talker_id::qzss;
    }
    return id;
}
 
float nmea::coord(const unsigned int degrees_chars, const std::string_view& sv) {
    std::string s(sv);
    // a float (and a double) may not precisely represent the value in the message
    float coord = std::stof(s.substr(0, degrees_chars), nullptr);
    coord += std::stof(s.substr(degrees_chars), nullptr) / 60.0;
    return coord;
}
 
direction nmea::dir(const std::string_view& sv) {
    assert(sv.starts_with('N') ||
            sv.starts_with('S') ||
            sv.starts_with('E') ||
            sv.starts_with('W'));
    direction d = direction::n;
    if (sv.starts_with('N')) {
        d = direction::n;
    } else if (sv.starts_with('S')) {
        d = direction::s;
    } else if (sv.starts_with('E')) {
        d = direction::e;
    } else if (sv.starts_with('W')) {
        d = direction::w;
    }
    return d;
}
 
void nmea::time(const std::string_view& sv, time_t& t) {
    std::string s(sv);
        t = time_t{
            std::chrono::hours(std::stoi(s.substr(0,  2))) +
            std::chrono::minutes(std::stoi(s.substr(2,  2))) +
            std::chrono::seconds(std::stoi(s.substr(4,  2))) +
            std::chrono::milliseconds(std::stoi(s.substr(7)))
    };
}
 
void nmea::date(const std::string_view& sv, std::chrono::year_month_day& d) {
    std::string s(sv);
// NMEA returns two digits, and not all systems know what century we are in.
// Current solution: use the century defined in source code.
// alternative could be to convert to stream and use formatter to parse 2 digit year
// but that's a bit much for our use case
#define CENTURY (2000)
    d = std::chrono::year_month_day{
            std::chrono::year(std::stoi(s.substr(4)) + CENTURY), 
            std::chrono::month(std::stoi(s.substr(2,  2))),
            std::chrono::day(std::stoi(s.substr(0,  2)))
    };
#undef CENTURY
}
 
bool nmea::valid(const std::string_view& sv) {
    assert(sv.starts_with('A') ||
            sv.starts_with('V'));
    return sv.starts_with('A');
}
 
quality nmea::qual(const std::string_view& sv) {
    // the typecast from int to enem<unsigned int> below is confirmed
    // to be safe in this case
    // https://www.modernescpp.com/index.php/strongly-typed-enums/
    return static_cast<quality>(std::stoi(std::string(sv)));
}
 
// $GPGLL,<Lat>,<N/S>,<Long>,<E/W>,<Timestamp>,<Status>,<mode indicator>*<checksum><cr><lf>
bool gll::from_data(const std::string& data, gll& gll) {
    unsigned int field = 0;
    for (const auto word : std::views::split(data, delim)) {
        switch (field) {
        case 0: // talker id
            gll.source = nmea::talker(std::string_view(word));
            break;
        case 1: // latitude
            gll.lat = nmea::coord(2, std::string_view(word));
            break;
        case 2: // latitude direction
            if (nmea::dir(std::string_view(word)) == direction::s) {
                gll.lat = gll.lat * -1;
            }
            break;
        case 3: // longitude
            gll.lon = nmea::coord(3, std::string_view(word));
            break;
        case 4: // longitude direction
            if (nmea::dir(std::string_view(word)) == direction::w) {
                gll.lon = gll.lon * -1;
            }
            break;
        case 5: // timestamp
            nmea::time(std::string_view(word), gll.t);
            break;
        case 6: // valid
            gll.valid = nmea::valid(std::string_view(word));
            break;
        default: // skip 7
            break;
        }
        field++;
    }
    return (field == 8); // everything parsed
}
 
// $GPGGA,<Timestamp>,<Lat>,<N/S>,<Long>,<E/W>,<GPSQual>,<Sats>,<HDOP>,<Alt>,<AltVal>,<GeoSep>,
// <GeoVal>,<DGPSAge>,<DGPSRef>*<checksum><cr><lf>
bool gga::from_data(const std::string& data, gga& gga) {
    unsigned int field = 0;
    for (const auto word : std::views::split(data, delim)) {
        switch (field) {
        case 0: // talker id
            gga.source = nmea::talker(std::string_view(word));
            break;
        case 1: // timestamp
            nmea::time(std::string_view(word), gga.t);
            break;
        case 2: // latitude
            gga.lat = nmea::coord(2, std::string_view(word));
            break;
        case 3: // latitude direction
            if (nmea::dir(std::string_view(word)) == direction::s) {
                gga.lat = gga.lat * -1;
            }
            break;
        case 4: // longitude
            gga.lon = nmea::coord(3, std::string_view(word));
            break;
        case 5: // longitude direction
            if (nmea::dir(std::string_view(word)) == direction::w) {
                gga.lon = gga.lon * -1;
            }
            break;
        case 6: // qual
            gga.qual = nmea::qual(std::string_view(word));
            break;
        case 7: // sats
            gga.sats = std::stoi(std::string(std::string_view(word)));
            break;
        case 9: // altitude (in meters)
            // a float (and a double) may not precisely represent the value in the message
            gga.alt = std::stof(std::string(std::string_view(word)), nullptr);
            break;      
        case 11: // geoid separation (in meters)
            // a float (and a double) may not precisely represent the value in the message
            gga.geosep = std::stof(std::string(std::string_view(word)), nullptr);
            break;      
        default: // skip 8, 10, 12 .. 15
            break;
        }
        field++;
    }
    return (field == 15); // everything parsed
}
 
// $GNGSA,A,3,15,18,,,,,,,,,,,4.7,3.7,2.9*2D
// $GNGSA,A,3,73,65,81,,,,,,,,,,4.7,3.7,2.9*2E
bool gsa::from_data(const std::string& data, gsa& gsa) {
    unsigned int field = 0;
    std::string_view v = std::string_view(data).substr(0, data.find('*'));
    for (const auto word : std::views::split(v, delim)) {
        switch (field) {
        case 0: // talker id
            gsa.source = nmea::talker(std::string_view(word));
            break;
        case 3:
        case 4:
        case 5:
        case 6:
        case 7:
        case 8:
        case 9:
        case 10:
        case 11:
        case 12:
        case 13:
        case 14:
            if (std::string_view(word).length() == 0) {
                gsa.sats[field - 3] = 0;
            } else {
                gsa.sats[field - 3] =
                        std::stoi(std::string(std::string_view(word)));
            }
            break;
        case 15:
            gsa.system_id = nmea::system(std::string_view(word));
            break;
        default: // skip 1,2, 16, 17
            break;
        }
        field++;
    }
    return (field == 18); // everything parsed
}
 
// $GPGSV,3,1,11,13,79,310,,14,53,113,,05,51,214,,30,47,067,*72
// $GPGSV,3,2,11,15,45,295,24,22,44,145,,20,27,192,,07,16,064,*7A
// $GPGSV,3,3,11,18,16,298,25,24,08,249,,08,08,029,18,,,,*40
// $GLGSV,2,1,08,72,79,113,,74,77,084,,75,38,202,,65,37,317,28*68
// $GLGSV,2,2,08,73,34,040,35,71,28,130,,81,13,333,24,82,08,017,*68
bool gsv::from_data(const std::string& data, gsv& gsv) {
    unsigned int field = 0;
    std::string_view v = std::string_view(data).substr(0, data.find('*'));
    for (const auto word : std::views::split(v, delim)) {
        switch (field) {
        case 0: // talker id
            gsv.source = nmea::talker(std::string_view(word));
            break;
        case 4:
        case 8:
        case 12:
        case 16:
            if (std::string_view(word).length() == 0) {
                gsv.sats[(field - 4) / 4 ].prn = 0;
            } else {
                gsv.sats[(field - 4) / 4 ].prn =
                        std::stoi(std::string(std::string_view(word)));
            }
            break;
        case 5:
        case 9:
        case 13:
        case 17:
            if (std::string_view(word).length() == 0) {
                gsv.sats[(field - 5) / 4 ].elev = 0;
            } else {
                gsv.sats[(field - 5) / 4 ].elev =
                        std::stoi(std::string(std::string_view(word)));
            }
            break;
        case 6:
        case 10:
        case 14:
        case 18:
            if (std::string_view(word).length() == 0) {
                gsv.sats[(field - 6) / 4 ].azim = 0;
            } else {
                gsv.sats[(field - 6) / 4 ].azim =
                        std::stoi(std::string(std::string_view(word)));
            }
            break;
        case 7:
        case 11:
        case 15:
        case 19:
            if (std::string_view(word).length() == 0) {
                gsv.sats[(field - 7) / 4 ].snr = 0;
            } else {
                gsv.sats[(field - 7) / 4 ].snr =
                        std::stoi(std::string(std::string_view(word)));
            }
            break;
        default: // skip 1, 2, 3
            break;
        }
        field++;
    }
    return (field == 20); // everything parsed
}
 
// $GPRMC,185427.150,V,5051.83778,N,00422.55809,E,,,240724,,,N*7F
bool rmc::from_data(const std::string& data, rmc& rmc) {
    unsigned int field = 0;
    for (const auto word : std::views::split(data, delim)) {
        switch (field) {
        case 0: // talker id
            rmc.source = nmea::talker(std::string_view(word));
            break;
        case 1: // timestamp
            nmea::time(std::string_view(word), rmc.t);
            break;
        case 2: // valid
            rmc.valid = nmea::valid(std::string_view(word));
            break;
        case 3: // latitude
            rmc.lat = nmea::coord(2, std::string_view(word));
            break;
        case 4: // latitude direction
            if (nmea::dir(std::string_view(word)) == direction::s) {
                rmc.lat = rmc.lat * -1;
            }
            break;
        case 5: // longitude
            rmc.lon = nmea::coord(3, std::string_view(word));
            break;
        case 6: // longitude direction
            if (nmea::dir(std::string_view(word)) == direction::w) {
                rmc.lon = rmc.lon * -1;
            }
            break;
        case 9: // dqtestamp
            nmea::date(std::string_view(word), rmc.d);
            break;
        default: // skip 7, 8, 10, 11, 12
            break;
        }
        field++;
    }
    return (field == 13); // everything parsed
}
 
} // namespace nmea