From 1217954524aa68d4850761f674f78c47f3e388c5 Mon Sep 17 00:00:00 2001
From: Derrick Brashear <shadow@gmail.com>
Date: Sun, 3 Nov 2002 06:18:43 +0000
Subject: patch from Tom Mayo, N1MU

---
 CHANGELOG    |  2 ++
 README       |  3 +++
 gpsd.c       |  6 ++++++
 nmea.h       |  2 ++
 nmea_parse.c | 21 +++++++++++++++++++++
 5 files changed, 34 insertions(+)

diff --git a/CHANGELOG b/CHANGELOG
index f62c4892..5190529b 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -36,3 +36,5 @@
 	 where they were not needed.
 20021003 (1.08)
 	 Added sockopt SO_REUSEADDR to netlib.c passive_sock.
+20021103 (1.09)
+	 G or g command returns six-digit Maidenhead grid square (like FN12fx)
diff --git a/README b/README
index e08f202c..354ce674 100644
--- a/README
+++ b/README
@@ -63,6 +63,9 @@ for the Earthmate.
 Curt Mills <BowHunter@mail.com> (WE7U) furthered the dgps support,
 writing the portion for other GPS receivers.
 
+Tom Mayo <tmayo1@rochester.rr.com> N1MU contributed the G/g command,
+which returns a 6 digit Maidenhead grid square.
+
 Be advised: any bugs in this code are mine, and mine only ;-)
 
 Thanks for Russ Nelson for providing a home for gpsd!
diff --git a/gpsd.c b/gpsd.c
index 3fecd2ab..88008e3a 100644
--- a/gpsd.c
+++ b/gpsd.c
@@ -505,6 +505,12 @@ static int handle_request(int fd, fd_set * fds)
 		    ",V=%f",
 		    gNMEAdata.speed);
 	    break;
+	case 'G':
+	case 'g':
+	    sprintf(reply + strlen(reply),
+		    ",G=%6.6s",
+		    gNMEAdata.grid);
+	    break;
 	case 'R':
 	case 'r':
 	    if (FD_ISSET(fd, fds)) {
diff --git a/nmea.h b/nmea.h
index bc1065fe..b893daaa 100644
--- a/nmea.h
+++ b/nmea.h
@@ -17,6 +17,8 @@ struct OUTDATA {
 
     double longitude;
 
+    char grid[7];
+
     double altitude;		/* Altitude in meters */
 
     double speed;		/* Speed over ground, knots */
diff --git a/nmea_parse.c b/nmea_parse.c
index 4ed82911..0c5c77e5 100644
--- a/nmea_parse.c
+++ b/nmea_parse.c
@@ -6,6 +6,7 @@
 
 extern struct OUTDATA gNMEAdata;
 static void do_lat_lon(char *sentence, int begin);
+static void do_grid(void);
 static char *field(char *sentence, short n);
 
 static void update_field_i(char *sentence, int fld, int *dest, int mask);
@@ -72,6 +73,7 @@ void processGPRMC(char *sentence)
     sscanf(field(sentence, 8), "%lf", &gNMEAdata.track);
 
     do_lat_lon(sentence, 3);
+    do_grid();
 
 }
 
@@ -88,6 +90,7 @@ void processGPVTG(char *sentence)
 void processGPGGA(char *sentence)
 {
     do_lat_lon(sentence, 2);
+    do_grid();
     /* 0 = none, 1 = normal, 2 = diff */
     sscanf(field(sentence, 6), "%d", &gNMEAdata.status);
     if ((gNMEAdata.status > 0) && (gNMEAdata.mode < 2))
@@ -188,6 +191,24 @@ static void do_lat_lon(char *sentence, int begin)
     }
 }
 
+/* ----------------------------------------------------------------------- */
+
+static void do_grid() {
+  double lat, lon;
+
+  lat = gNMEAdata.latitude;
+  lon = gNMEAdata.longitude;
+
+  gNMEAdata.grid[0] = 65 + (int)((180.0 + lon) / 20.0);
+  gNMEAdata.grid[1] = 65 + (int)((90.0 + lat) / 10.0);
+  gNMEAdata.grid[2] = 48 + (int)((180.0 + lon) / 2) % 10;
+  gNMEAdata.grid[3] = 48 + (int)(90.0 + lat) % 10;
+  gNMEAdata.grid[4] = 97 + ((int)(180.0 + lon) % 2) * 12 + (int)(((180.0 + lon) - (int)(180.0 + lon)) * 12);
+  gNMEAdata.grid[5] = 97 + (int)(((90.0 + lat) - (int)(90.0 + lat)) * 24);
+  gNMEAdata.grid[6] = '\0';
+}
+
+/* ----------------------------------------------------------------------- */
 
 static void update_field_i(char *sentence, int fld, int *dest, int mask)
 {
-- 
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