Add latlon_to_grid function

README.md

@@ -261,6 +261,22 @@ Public Methods
 */
 ```
 
+### latlon_to_grid()
+```
+/*
+ * latlon_to_grid(float lat, float lon, char* ret_grid)
+ *
+ * Takes a station latitude and longitude provided in decimal degrees format and
+ * returns a string with the 6-digit Maidenhead grid designator.
+ *
+ * lat - Latitude in decimal degrees format.
+ * lon - Longitude in decimal degrees format.
+ * ret_grid - Derived Maidenhead grid square. A pointer to a character array of
+ *   at least 7 bytes must be provided here for the function return value.
+ *
+ */
+ ```
+
 Tokens
 ------
 Here are the defines, structs, and enumerations you will find handy to use with the library.
@@ -277,6 +293,10 @@ Also, a big thank you to Murray Greenman, ZL1BPU for working allowing me to pick
 
 Changelog
 ---------
+* v1.3.1
+
+    * Added latitude/longitude to Maidenhead grid convenience function
+
 * v1.3.0
 
     * WSPR Type 2 and Type 3 message capability added

library.properties

@@ -1,5 +1,5 @@
 name=Etherkit JTEncode
-version=1.3.0
+version=1.3.1
 author=Jason Milldrum <milldrum@gmail.com>
 maintainer=Jason Milldrum <milldrum@gmail.com>
 sentence=Generate JT65, JT9, JT4, FT8, WSPR, and FSQ symbols on your Arduino.

src/JTEncode.cpp

@@ -445,6 +445,46 @@ void JTEncode::ft8_encode(const char * msg, uint8_t * symbols)
   ft8_merge_sync_vector(s, symbols);
 }
 
+/*
+ * latlon_to_grid(float lat, float lon, char* ret_grid)
+ *
+ * Takes a station latitude and longitude provided in decimal degrees format and
+ * returns a string with the 6-digit Maidenhead grid designator.
+ *
+ * lat - Latitude in decimal degrees format.
+ * lon - Longitude in decimal degrees format.
+ * ret_grid - Derived Maidenhead grid square. A pointer to a character array of
+ *   at least 7 bytes must be provided here for the function return value.
+ *
+ */
+void JTEncode::latlon_to_grid(float lat, float lon, char* ret_grid)
+{
+  char grid[7];
+  memset(grid, 0, 7);
+
+  // Normalize lat and lon
+  lon += 180.0;
+  lat += 90.0;
+
+  // Derive first coordinate pair
+  grid[0] = (char)((uint8_t)(lon / 20) + 'A');
+  grid[1] = (char)((uint8_t)(lat / 10) + 'A');
+
+  // Derive second coordinate pair
+  lon = lon - ((uint8_t)(lon / 20) * 20);
+  lat = lat - ((uint8_t)(lat / 10) * 10);
+  grid[2] = (char)((uint8_t)(lon / 2) + '0');
+  grid[3] = (char)((uint8_t)(lat) + '0');
+
+  // Derive third coordinate pair
+  lon = lon - ((uint8_t)(lon / 2) * 2);
+  lat = lat - ((uint8_t)(lat));
+  grid[4] = (char)((uint8_t)(lon * 12) + 'a');
+  grid[5] = (char)((uint8_t)(lat * 24) + 'a');
+
+  strncpy(ret_grid, grid, 6);
+}
+
 /* Private Class Members */
 
 uint8_t JTEncode::jt_code(char c)

src/JTEncode.h

@@ -225,6 +225,7 @@ public:
   void fsq_encode(const char *, const char *, uint8_t *);
   void fsq_dir_encode(const char *, const char *, const char, const char *, uint8_t *);
   void ft8_encode(const char *, uint8_t *);
+  void latlon_to_grid(float, float, char*);
 private:
   uint8_t jt_code(char);
   uint8_t ft_code(char);