00001 #include <grass/gis.h>
00002
00003
00004 #define ZERO(x) x < tolerance && x > -tolerance
00005 #define TOLERANCE 1.0e-10
00006 static double tolerance = TOLERANCE;
00007
00008 int G_set_distance_to_line_tolerance(double t)
00009 {
00010 if (t <= 0.0)
00011 t = TOLERANCE;
00012 tolerance = t;
00013
00014 return 0;
00015 }
00016
00017 double G_distance2_point_to_line(double x, double y,
00018 double x1, double y1, double x2, double y2)
00019 {
00020 double dx, dy, t;
00021
00022 dx = x2 - x1;
00023 dy = y2 - y1;
00024
00025 if (ZERO(dx) && ZERO(dy)) {
00026 dx = x1 - x;
00027 dy = y1 - y;
00028 return dx * dx + dy * dy;
00029 }
00030
00031 t = (dx * (x - x1) + dy * (y - y1)) / (dx * dx + dy * dy);
00032
00033 if (t < 0.0) {
00034 dx = x - x1;
00035 dy = y - y1;
00036 }
00037 else if (t > 1.0) {
00038 dx = x - x2;
00039 dy = y - y2;
00040 }
00041 else {
00042
00043 dx = x - (dx * t + x1);
00044 dy = y - (dy * t + y1);
00045 }
00046 return dx * dx + dy * dy;
00047 }