src/main/common/gps_conversion.c

   1 /*
   2  * This file is part of Cleanflight.
   3  *
   4  * Cleanflight is free software: you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation, either version 3 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * Cleanflight is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with Cleanflight.  If not, see <http://www.gnu.org/licenses/>.
  16  */
  17
  18 #include <stdbool.h>
  19 #include <stdint.h>
  20 #include <ctype.h>
  21 #include <string.h>
  22
  23 #include "platform.h"
  24
  25 #ifdef USE_GPS
  26
  27
  28 #define DIGIT_TO_VAL(_x)    (_x - '0')
  29 uint32_t GPS_coord_to_degrees(const char* coordinateString)
  30 {
  31     const char *fieldSeparator, *remainingString;
  32     uint8_t degress = 0, minutes = 0;
  33     uint16_t fractionalMinutes = 0;
  34     uint8_t digitIndex;
  35
  36     // scan for decimal point or end of field
  37     for (fieldSeparator = coordinateString; isdigit((unsigned char)*fieldSeparator); fieldSeparator++) {
  38         if (fieldSeparator >= coordinateString + 15)
  39             return 0; // stop potential fail
  40     }
  41     remainingString = coordinateString;
  42
  43     // convert degrees
  44     while ((fieldSeparator - remainingString) > 2) {
  45         if (degress)
  46             degress *= 10;
  47         degress += DIGIT_TO_VAL(*remainingString++);
  48     }
  49     // convert minutes
  50     while (fieldSeparator > remainingString) {
  51         if (minutes)
  52             minutes *= 10;
  53         minutes += DIGIT_TO_VAL(*remainingString++);
  54     }
  55     // convert fractional minutes
  56     // expect up to four digits, result is in
  57     // ten-thousandths of a minute
  58     if (*fieldSeparator == '.') {
  59         remainingString = fieldSeparator + 1;
  60         for (digitIndex = 0; digitIndex < 4; digitIndex++) {
  61             fractionalMinutes *= 10;
  62             if (isdigit((unsigned char)*remainingString))
  63                 fractionalMinutes += *remainingString++ - '0';
  64         }
  65     }
  66     return degress * 10000000UL + (minutes * 1000000UL + fractionalMinutes * 100UL) / 6;
  67 }
  68 #endif