Merge pull request cbassa#19 from kerel-fs/pr/satmap_help

satmap: Add usage & interactive usage help

README.md

@@ -96,6 +96,12 @@ Tools
   - Append `-P` in order to invoke `skymap` to plot a skymap and the
     sky track for each predicted pass
 
+* `satmap`: Visualize satellite tracks on a map of Earth
+  Example usage:
+  - Show the ground track of all satellites in `ST_TLEDIR/classfd.tle` (for roughly 1.3 orbits from now on)
+    ```
+    satmap
+    ```
 * `satorbit`: Show a 3D representation of the earth, the current position,
   footprint and orbit of the selected object
   Example usage:

satmap.c

@@ -53,6 +53,7 @@ double nfd2mjd(char *date);
 double date2mjd(int year,int month,double day);
 void mjd2date(double mjd,char *date,int length);
 void usage();
+void interactive_usage();
 void nfd_now(char *s);
 double gmst(double);
 double dgmst(double);
@@ -490,6 +491,13 @@ void plot_map(void)
     // Get cursor
     cpgcurs(&x,&y,&c);
 
+    // Help
+    if (c=='h') {
+      interactive_usage();
+
+      continue;
+    }
+
     // Redraw
     if (c=='r') {
       m.mjd=-1.0;
@@ -695,7 +703,23 @@ double nfd2mjd(char *date)
 
 void usage()
 {
-  return;
+  printf("usage: satmap -c TLEFILE [-t TIMESTAMP] [-s COSPARID] [-i SATNO]\n");
+  printf("                [-l LENGTH] [-h]\n");
+}
+
+void interactive_usage()
+{
+  printf("Interactive help:");
+  printf("r    Redraw\n");
+  printf("\n");
+  printf("<    Divide the integration length by a facor of 2\n");
+  printf(">    Multiply the integration length by a facor of 2\n");
+  printf("\n");
+  printf(",    Increase time (+integration_length in seconds /(1 day))\n");
+  printf(".    Roll back the time\n");
+  printf("\n");
+  printf("h    this interactive help\n");
+  printf("q/Q  Exit\n");
 }
 
 // Compute Date from Julian Day