Ticket #76: d.measure_bearing.patch

d.measure/local_proto.h

@@ -1 +1 @@
 /* draw_line.c */
 int draw_line(int, int, int, int, int, int);
 /* msurements.c */
-int measurements(int, int, int, int, int);
+int measurements(int, int, int, int, int, int, int);
 int print_en(double, double, int);
 int print_length(double, int, int);
+int print_bearing_deg (double, double, double, double, int, int);
 int add_point(double **, double **, int *, int *, double, double);

d.measure/msurements.c

@@ -2 +2 @@
 #include <grass/display.h>
 #include <grass/raster.h>
 #include "local_proto.h"
+#include <math.h>
+#include <unistd.h>
 
+#define PI  M_PI
 
 FILE *output;
 
-int measurements(int color1,int color2, int s_flag, int m_flag, int k_flag)
+int measurements(int color1,int color2, int s_flag, int m_flag, int k_flag, int b_flag, int c_flag)
 {
     double *x, *y;
     int npoints, nalloc;
@@ -89 +92 @@
                 draw_line(screen_x,screen_y,cur_screen_x,cur_screen_y,color1,color2)  ;
                 add_point (&x, &y, &npoints, &nalloc, ux, uy);
                 length += G_distance(cur_ux, cur_uy, ux, uy) ;
+                
+                if(b_flag)
+                                        print_bearing_deg(cur_ux, ux, cur_uy, uy, s_flag, c_flag);
+                                        
                 print_length(length, s_flag, k_flag);
+                
+                
+                
                 cur_screen_x = screen_x ;
                 cur_screen_y = screen_y ;
                 cur_ux = ux ;
@@ -163 +173 @@
     return 0;
 }
 
+/**
+\brief compute the bearing in degrees from click to next click. 
+
+\note North is at 90 degrees by default
+\note north can be shifted to 0 degrees, and increment degrees increase counter-clockwise (like a compass) with the '-c' flag
+*/
+int print_bearing_deg (double cur_ux, double ux, double cur_uy, double uy, int s_flag, int c_flag)
+{       
+        double bearing_deg ;
+        double dx, dy;
+        
+    /* Use stderr for TCLTK-Output */
+    if( s_flag )
+      output = stderr;
+    else
+      output = stdout;
+        
+        dx = ux - cur_ux ;
+        dy = uy - cur_uy ;
+        
+        /* format output to compass-like bearings:
+        
+           put north at 0 deg by subtracting PI/2 
+           set to counter-clockwise like a compass by setting 'dx' to '-dx' */
+        if( c_flag)
+                {
+                bearing_deg = (atan2(dy, -dx) - PI/2) * 180/PI ;
+                if(bearing_deg < 0)
+                        bearing_deg = 360 + bearing_deg;
+                }
+        
+        /* standard math-style
+           north is at 90 deg */
+        else
+                bearing_deg = atan2(dy, dx) * 180/PI ;
+        
+    fprintf (output,"Bearing:   %3.2f degrees\n", bearing_deg) ;
+
+    return 0;
+}
+
 int add_point (double **x, double **y,
     int *npoints, int *nalloc, double ux, double uy)
 {

d.measure/main.c

@@ -20 +20 @@
  *
  *****************************************************************************/
 #include <stdlib.h>
+
 #include <grass/gis.h>
 #include <grass/display.h>
 #include <grass/raster.h>
@@ -38 +39 @@
            struct Flag *s;
            struct Flag *m;
            struct Flag *k;
+           struct Flag *b;
+           struct Flag *c;
         } parm;
-        int color1, color2, s_flag, m_flag, k_flag;
+        int color1, color2, s_flag, m_flag, k_flag, b_flag, c_flag;
 
         /* Initialize the GIS calls */
         G_gisinit(argv[0]) ;
@@ -79 +82 @@
         parm.k->key = 'k';
         parm.k->description = _("Output in kilometers as well");
         
+        parm.b = G_define_flag();
+        parm.b->key = 'b';
+        parm.b->description = _("Compute bearing between points, relative to x-axis (north is 90 degrees)");
+        
+        parm.c = G_define_flag();
+        parm.c->key = 'c';
+        parm.c->description = _("Use compass-style bearing (north is 0 degrees, increases CCW)");
+        
         if (argc > 1 && G_parser(argc,argv))
             exit(EXIT_FAILURE);
 
@@ -91 +102 @@
         if (D_set_cur_wind(frame))
             G_fatal_error(_("Current frame not available"));
 
+        /* test for bearing calculation request in a LL location */
+                if (parm.b->answer && G_projection() == PROJECTION_LL)
+                        G_fatal_error(_("bearing calculation is not available for LL projection"));
+                        
+        /* issue an error if the c flag is issued without the b flag */
+        if (parm.c->answer && !parm.b->answer)
+                        G_fatal_error(_("the -c flag can only be used in conjunction with the -b flag"));
+        
         color1 = D_translate_color (parm.c1->answer);
         color2 = D_translate_color (parm.c2->answer);
         s_flag = parm.s->answer;
         m_flag = parm.m->answer;
         k_flag = parm.k->answer;
+        b_flag = parm.b->answer;
+        c_flag = parm.c->answer;
 
-        measurements(color1, color2, s_flag, m_flag, k_flag ) ;
+        measurements(color1, color2, s_flag, m_flag, k_flag, b_flag, c_flag ) ;
 
         R_close_driver();
 

d.measure/description.html

@@ -35 +35 @@
 If the user draws an area within another area, the combined 
 area of both regions will be output. 
 
+<EM>Bearing Calculations</EM>
+Calcuation of bearings can be done in two ways:
+<ol>
+<li>math-style: angles are computed relative to the positive x-axis, with the starting point at the origin (north at 90 degrees)</li>
+<li>compass-style: angles are computed relative to the positive y-axis, with the starting point at the origin (north at 0 degrees)</li>
+</ol>
+
 <H2>TODO</H2>
 
 Output lengths in the same units as those of the current LOCATION as