From 7af3945a91a368cbb56db273f15ffe03203b2fa4 Mon Sep 17 00:00:00 2001 From: Kosma Moczek Date: Fri, 14 Feb 2014 15:39:29 +0100 Subject: [PATCH] README.md: document number and coordinate format --- README.md | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/README.md b/README.md index 36a6d40..d532dba 100644 --- a/README.md +++ b/README.md @@ -21,6 +21,31 @@ systems. Adding support for more sentences is trivial; see ``minmea.c`` source. +## Fractional number format + +Internally, minmea stores fractional numbers as pairs of two integers: ``(value, scale)``. +For example, a value of ``"-123.456"`` would be parsed as ``(-123456, 1000)``. As this +format is quite unwieldy, minmea provides the following convenience macros for converting +to either fixed-point or floating-point format: + +* ``minmea_rescale(-123456, 1000, 10) => -1235`` +* ``minmea_float(-123456, 1000) => -123.456`` + +## Coordinate format + +NMEA uses the clunky ``DDMM.MMMM`` format which, honestly, is not good in the internet era. +Internally, minmea stores it as a fractional number (see above); for practical uses, +the value should be probably converted to the DD.DDDDD floating point format using the +following macro: + +* ``minmea_coord(-375165, 100) => -37.860832`` + +The library doesn't perform this conversion automatically for the following reasons: + +* The conversion is not reversible. +* It requires floating point hardware. +* The user might want to perform this conversion later on or retain the original values. + ## Example ```c