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/*!
\file tin.c
\brief Vector library - TIN
Higher level functions for reading/writing/manipulating vectors.
(C) 2001-2008 by the GRASS Development Team
This program is free software under the
GNU General Public License (>=v2).
Read the file COPYING that comes with GRASS
for details.
\author Radim Blazek
\date 2001
*/
#include <grass/Vect.h>
/*!
\brief Calculates z coordinate for point from TIN
\param Map pointer to vector map
\param tx,ty point coordinates
\param[out] tz z-coordinate of point
\param[out] angle angle
\param[out] slope slope
\return 1 on success,
\return 0 point is not in area,
\return -1 area has not 4 points or has island
*/
int
Vect_tin_get_z(struct Map_info *Map,
double tx, double ty, double *tz, double *angle, double *slope)
{
int i, area, n_points;
struct Plus_head *Plus;
P_AREA *Area;
static struct line_pnts *Points;
static int first_time = 1;
double *x, *y, *z;
double vx1, vx2, vy1, vy2, vz1, vz2;
double a, b, c, d;
/* TODO angle, slope */
Plus = &(Map->plus);
if (first_time == 1) {
Points = Vect_new_line_struct();
first_time = 0;
}
area = Vect_find_area(Map, tx, ty);
G_debug(3, "TIN: area = %d", area);
if (area == 0)
return 0;
Area = Plus->Area[area];
if (Area->n_isles > 0)
return -1;
Vect_get_area_points(Map, area, Points);
n_points = Points->n_points;
if (n_points != 4)
return -1;
x = Points->x;
y = Points->y;
z = Points->z;
for (i = 0; i < 3; i++) {
G_debug(3, "TIN: %d %f %f %f", i, x[i], y[i], z[i]);
}
vx1 = x[1] - x[0];
vy1 = y[1] - y[0];
vz1 = z[1] - z[0];
vx2 = x[2] - x[0];
vy2 = y[2] - y[0];
vz2 = z[2] - z[0];
a = vy1 * vz2 - vy2 * vz1;
b = vz1 * vx2 - vz2 * vx1;
c = vx1 * vy2 - vx2 * vy1;
d = -a * x[0] - b * y[0] - c * z[0];
/* OK ? */
*tz = -(d + a * tx + b * ty) / c;
G_debug(3, "TIN: z = %f", *tz);
return 1;
}
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