GRASS GIS 8 Programmer's Manual  8.4.0dev(2024)-112dd97adf
vector/diglib/line_dist.c
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1 /*****************************************************************************
2  *
3  * MODULE: Vector library
4  *
5  * AUTHOR(S): Original author CERL, probably Dave Gerdes.
6  * Update to GRASS 5.7 Radim Blazek.
7  *
8  * PURPOSE: Lower level functions for reading/writing/manipulating vectors.
9  *
10  * COPYRIGHT: (C) 2001 by the GRASS Development Team
11  *
12  * This program is free software under the GNU General Public
13  * License (>=v2). Read the file COPYING that comes with GRASS
14  * for details.
15  *
16  *****************************************************************************/
17 
18 #include <math.h>
19 
20 #define ZERO(x) ((x) < tolerance && (x) > -tolerance)
21 #define TOLERANCE 1.0e-10
22 static double tolerance = TOLERANCE;
23 
25 {
26  if (t <= 0.0)
27  t = TOLERANCE;
28  tolerance = t;
29 
30  return 0;
31 }
32 
33 /*
34  * dig_distance2_point_to_line ()
35  * compute square of distance of point (x,y) to line segment (x1,y1 - x2,y2)
36  * ( works correctly for x1==x2 && y1==y2 )
37  *
38  * returns: square distance
39  * sets (if not NULL): *px, *py - nearest point on segment
40  * *pdist - distance of px,py from segment start
41  * *status = 0 if ok, -1 if t < 0 and 1 if t > 1
42  * (tells if point is w/in segment space, or
43  * past ends)
44  */
45 
46 double
47 dig_distance2_point_to_line(double x, double y, double z, /* point */
48  double x1, double y1, double z1, /* line segment */
49  double x2, double y2, double z2,
50  int with_z, /* use z coordinate, (3D calculation) */
51  double *px, double *py,
52  double *pz, /* point on segment */
53  double *pdist, /* distance of point on segment from
54  the first point of segment */
55  int *status)
56 {
57  register double dx, dy, dz;
58  register double dpx, dpy, dpz;
59  register double tpx, tpy, tpz;
60  double t;
61  int st;
62 
63  st = 0;
64 
65  if (!with_z) {
66  z = 0;
67  z1 = 0;
68  z2 = 0;
69  }
70 
71  dx = x2 - x1;
72  dy = y2 - y1;
73  dz = z2 - z1;
74 
75  if (ZERO(dx) && ZERO(dy) && ZERO(dz)) { /* line is degenerate */
76  dx = x1 - x;
77  dy = y1 - y;
78  dz = z1 - z;
79  tpx = x1;
80  tpy = y1;
81  tpz = z1;
82  }
83  else {
84  t = (dx * (x - x1) + dy * (y - y1) + dz * (z - z1)) /
85  (dx * dx + dy * dy + dz * dz);
86 
87  if (t <= 0.0) { /* go to x1,y1,z1 */
88  if (t < 0.0) {
89  st = -1;
90  }
91  tpx = x1;
92  tpy = y1;
93  tpz = z1;
94  }
95  else if (t >= 1.0) { /* go to x2,y2,z2 */
96  if (t > 1.0) {
97  st = 1;
98  }
99  tpx = x2;
100  tpy = y2;
101  tpz = z2;
102  }
103  else {
104  /* go t from x1,y1,z1 towards x2,y2,z2 */
105  tpx = dx * t + x1;
106  tpy = dy * t + y1;
107  tpz = dz * t + z1;
108  }
109  dx = tpx - x;
110  dy = tpy - y;
111  dz = tpz - z;
112  }
113 
114  if (px)
115  *px = tpx;
116  if (py)
117  *py = tpy;
118  if (pz)
119  *pz = tpz;
120  if (status)
121  *status = st;
122 
123  if (pdist) {
124  dpx = tpx - x1;
125  dpy = tpy - y1;
126  dpz = tpz - z1;
127  *pdist = sqrt(dpx * dpx + dpy * dpy + dpz * dpz);
128  }
129 
130  return (dx * dx + dy * dy + dz * dz);
131 }
struct state * st
Definition: parser.c:104
double t
Definition: r_raster.c:39
int dig_set_distance_to_line_tolerance(double t)
#define TOLERANCE
#define ZERO(x)
double dig_distance2_point_to_line(double x, double y, double z, double x1, double y1, double z1, double x2, double y2, double z2, int with_z, double *px, double *py, double *pz, double *pdist, int *status)
#define x