d973b98d66
This is a backwards-incompatible change that I knew I'd have to introduce sooner or later. Which means now. Long story short: when I first started writing this library, I wanted to make things simpler by treating the entire talker+sentence as one big ID. Of course, this is an oversimplification, as there are different talkers out there. Turns out they're more common than I initially thought. I just came across a module (read: I had one soldered to my board by our crazy hardware guy) that spits out GPRMC, GLRMC or GNRMC depending on where it got the data. I could have kludged around this, but here's this change, for the purity of code. Fortunately, we're the only users of this codebase as far as I know, so no real harm is done - but it's a lesson to design my interfaces right from the very start so I don't have to break compatibility and write apologetic messages later on.
127 lines
4.9 KiB
Markdown
127 lines
4.9 KiB
Markdown
# minmea, a lightweight GPS NMEA 0183 parser library
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Minmea is a minimalistic GPS parser library written in pure C intended for
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resource-constrained platforms, especially microcontrollers and other embedded
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systems.
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## Features
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* Written in ISO C99.
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* No dynamic memory allocation.
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* No floating point usage in the core library.
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* Supports both fixed and floating point values.
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* One source file and one header - can't get any simpler.
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* Easily extendable to support new sentences.
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* Complete with a test suite and static analysis.
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## Supported sentences
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* ``$GPRMC``
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* ``$GPGGA``
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* ``$GPGSA``
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Adding support for more sentences is trivial; see ``minmea.c`` source.
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## Fractional number format
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Internally, minmea stores fractional numbers as pairs of two integers: ``(value, scale)``.
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For example, a value of ``"-123.456"`` would be parsed as ``(-123456, 1000)``. As this
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format is quite unwieldy, minmea provides the following convenience macros for converting
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to either fixed-point or floating-point format:
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* ``minmea_rescale(-123456, 1000, 10) => -1235``
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* ``minmea_float(-123456, 1000) => -123.456``
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## Coordinate format
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NMEA uses the clunky ``DDMM.MMMM`` format which, honestly, is not good in the internet era.
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Internally, minmea stores it as a fractional number (see above); for practical uses,
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the value should be probably converted to the DD.DDDDD floating point format using the
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following macro:
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* ``minmea_coord(-375165, 100) => -37.860832``
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The library doesn't perform this conversion automatically for the following reasons:
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* The conversion is not reversible.
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* It requires floating point hardware.
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* The user might want to perform this conversion later on or retain the original values.
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## Example
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```c
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char line[MINMEA_MAX_LENGTH];
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while (fgets(line, sizeof(line), stdin) != NULL) {
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printf("%s", line);
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switch (minmea_sentence_id(line)) {
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case MINMEA_SENTENCE_RMC: {
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struct minmea_sentence_rmc frame;
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if (minmea_parse_rmc(&frame, line)) {
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printf("+++ raw coordinates and speed: (%d/%d,%d/%d) %d/%d\n",
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frame.latitude, frame.latitude_scale,
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frame.longitude, frame.longitude_scale,
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frame.speed, frame.speed_scale);
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printf("+++ fixed-point coordinates and speed scaled to three decimal places: (%d,%d) %d\n",
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minmea_rescale(frame.latitude, frame.latitude_scale, 1000),
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minmea_rescale(frame.longitude, frame.longitude_scale, 1000),
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minmea_rescale(frame.speed, frame.speed_scale, 1000));
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printf("+++ floating point degree coordinates and speed: (%f,%f) %f\n",
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minmea_coord(frame.latitude, frame.latitude_scale),
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minmea_coord(frame.longitude, frame.longitude_scale),
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minmea_float(frame.speed, frame.speed_scale));
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}
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} break;
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case MINMEA_SENTENCE_GGA: {
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struct minmea_sentence_gga frame;
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if (minmea_parse_gga(&frame, line)) {
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printf("$GPGGA: fix quality: %d\n", frame.fix_quality);
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}
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} break;
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}
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}
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```
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## Integration with your project
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Simply add ``minmea.[ch]`` to your project, ``#include "minmea.h"`` and you're
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good to go.
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## Running unit tests
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Building and running the tests requires the following:
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* Check Framework (http://check.sourceforge.net/).
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* Clang Static Analyzer (http://clang-analyzer.llvm.org/).
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If you have both in your ``$PATH``, running the tests should be as simple as
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typing ``make``.
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## Limitations
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* Fractional numbers are represented as ``int`` internally, which is 32 bits on
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most embedded platforms. Therefore, the maximum supported coordinate precision
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is ``[+-]DDDMM.MMMMM``. The library does not check for integer overflow at the
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moment; coordinates with more precision will not parse correctly.
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* Only a handful of frames is supported right now.
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* There's no support for omitting parts of the library from building. As
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a workaround, use the ``-ffunction-sections -Wl,--gc-sections`` linker flags
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(or equivalent) to remove the unused functions (parsers) from the final image.
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* Some systems lack ``timegm``. On these systems, the recommended course of
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action is to build with ``-Dtimegm=mktime`` - assuming the system runs in the
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default ``UTC`` timezone.
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## Bugs
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There are plenty. Report them on GitHub, or - even better - open a pull request.
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Please write unit tests for any new functions you add - it's fun!
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## Licensing
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Minmea is open source software; see ``COPYING`` for amusement. Email me if the
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license bothers you and I'll happily re-license under anything else under the sun.
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## Author
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Minmea was written by Kosma Moczek <kosma@cloudyourcar.com> at Cloud Your Car.
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