From 2e770cee8b679dcb8f8b06c053d208555aa58882 Mon Sep 17 00:00:00 2001
From: Zilog80 <rs1729@users.noreply.github.com>
Date: Fri, 12 Jun 2020 13:06:08 +0200
Subject: [PATCH] DFM: geoid data, MSL = alt_ellipsoid + dMSL

---
 demod/mod/dfm09mod.c | 31 +++++++++++++++++++++++++++----
 dfm/dfm06.txt        |  8 ++++++--
 2 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/demod/mod/dfm09mod.c b/demod/mod/dfm09mod.c
index d5372d5..7396514 100644
--- a/demod/mod/dfm09mod.c
+++ b/demod/mod/dfm09mod.c
@@ -52,6 +52,12 @@ typedef struct {
     ui32_t chX[2];
 } sn_t;
 
+typedef struct {
+    ui32_t prn; // SVs used (PRN)
+    float dMSL; // Alt_MSL - Alt_ellipsoid = -N = - geoid_height =  ellipsoid - geoid
+    ui8_t nSV; // numSVs used
+} gpsdat_t;
+
 #define BITFRAME_LEN  280
 
 typedef struct {
@@ -74,6 +80,7 @@ typedef struct {
     pcksts_t pck[9];
     option_t option;
     int ptu_out;
+    gpsdat_t gps;
 } gpx_t;
 
 
@@ -294,6 +301,9 @@ static int dat_out(gpx_t *gpx, ui8_t *dat_bits, int ec) {
         }
     }
 
+    // GPS data
+    // SiRF msg ID 41: Geodetic Navigation Data
+
     if (fr_id == 0) {
         //start = 0x1000;
         frnr = bits2val(dat_bits+24, 8);
@@ -301,7 +311,8 @@ static int dat_out(gpx_t *gpx, ui8_t *dat_bits, int ec) {
     }
 
     if (fr_id == 1) {
-        // 00..31: ? GPS-Sats in Sicht?
+        // 00..31: GPS-Sats in solution (bitmap)
+        gpx->gps.prn = bits2val(dat_bits, 32); // SV/PRN used
         msek = bits2val(dat_bits+32, 16);  // UTC (= GPS - 18sec  ab 1.1.2017)
         gpx->sek = msek/1000.0;
     }
@@ -328,6 +339,8 @@ static int dat_out(gpx_t *gpx, ui8_t *dat_bits, int ec) {
     }
 
     if (fr_id == 5) {
+        short dMSL = bits2val(dat_bits, 16);
+        gpx->gps.dMSL = dMSL/1e2;
     }
 
     if (fr_id == 6) { // sat data
@@ -342,6 +355,7 @@ static int dat_out(gpx_t *gpx, ui8_t *dat_bits, int ec) {
         gpx->tag   = bits2val(dat_bits+16, 5);
         gpx->std   = bits2val(dat_bits+21, 5);
         gpx->min   = bits2val(dat_bits+26, 6);
+        gpx->gps.nSV = bits2val(dat_bits+32, 8);
     }
 
     ret = fr_id;
@@ -733,6 +747,16 @@ static void print_gpx(gpx_t *gpx) {
         }
         printf("\n");
 
+        if (gpx->option.sat) {
+            printf("  ");
+            printf("  dMSL: %+.2f", gpx->gps.dMSL); // MSL = alt + gps.dMSL
+            printf("  sats: %d", gpx->gps.nSV);
+            printf("  (");
+            for (j = 0; j < 32; j++) { if ((gpx->gps.prn >> j)&1) printf(" %02d", j+1); }
+            printf(" )");
+            printf("\n");
+        }
+
         if (gpx->option.jsn && jsonout)
         {
             // JSON Buffer to store sonde ID
@@ -1058,6 +1082,7 @@ int main(int argc, char **argv) {
             option_min = 1;
         }
         else if   (strcmp(*argv, "--dbg") == 0) { gpx.option.dbg = 1; }
+        else if   (strcmp(*argv, "--sat") == 0) { gpx.option.sat = 1; }
         else if (strcmp(*argv, "-") == 0) {
             int sample_rate = 0, bits_sample = 0, channels = 0;
             ++argv;
@@ -1122,7 +1147,6 @@ int main(int argc, char **argv) {
     gpx.option.dst = option_dist;
     gpx.option.jsn = option_json;
 
-
     headerlen = strlen(dfm_rawheader);
 
 
@@ -1259,7 +1283,6 @@ int main(int argc, char **argv) {
                         // optional:
                         // normalize soft bit s_j by
                         //   rhsbit.sb /= dsp._spb+1; // all samples in [-1,+1]
-
                     }
                     if ( bitQ == EOF ) { frm = nfrms; break; } // liest 2x EOF
 
@@ -1285,12 +1308,12 @@ int main(int argc, char **argv) {
         pos = headerlen;
     }
 
+
     if (!option_bin) free_buffers(&dsp);
     else {
         if (hdb.buf) { free(hdb.buf); hdb.buf = NULL; }
     }
 
-
     fclose(fp);
 
     return 0;
diff --git a/dfm/dfm06.txt b/dfm/dfm06.txt
index ff16990..7fe94e2 100644
--- a/dfm/dfm06.txt
+++ b/dfm/dfm06.txt
@@ -15,12 +15,14 @@ erweiterter systematischer [8,4]-Hamming-Code, erste 4 bit sind Daten
 Big Endian
 
 
+(SiRF msg ID 41: Geodetic Navigation Data)
 GPS_DAT-Block 48bit + 4bit-PCK_ID 0x0..0x8 (letztes nibble):
 PCK_ID  bitpos
 
 0x0     24..31   Counter: 8 bit
 
-0x1     32..47   UTC-msec : 16bit  (sec*1e3),  GPS = UTC + 18s (ab 1. Jan. 2017)
+0x1      0..31   SV/PRN bitmap
+        32..47   UTC-msec : 16bit  (sec*1e3),  GPS = UTC + 18s (ab 1. Jan. 2017)
 
 0x2      0..31   GPS-lat  : 32bit, Faktor 1e7
         32..47   hor-V m/s: 16bit, Faktor 1e2
@@ -28,9 +30,11 @@ PCK_ID  bitpos
 0x3      0..31   GPS-lon  : 32bit, Faktor 1e7
         32..47   direction: 16bit, Faktor 1e2 (unsigned, 0-36000)
 
-0x4      0..31   GPS-alt m: 32bit, Faktor 1e2
+0x4      0..31   GPS-alt m: 32bit, Faktor 1e2 (Alt_ellipsoid)
         32..47   ver-V m/s: 16bit, Faktor 1e2 (signed)
 
+0x5      0..15   dMSL = Alt_MSL - Alt_ellipsoid = -N = -geoid_height , Faktor 1e2 (signed)
+
 0x8      0..11   Jahr : 12bit
         12..15   Monat:  4bit
         16..20   Tag  :  5bit