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/*
* $Id: angle.c,v 1.5 2003/09/11 16:12:48 markus Exp $
*
****************************************************************************
*
* MODULE: Vector library
*
* AUTHOR(S): Original author CERL, probably Dave Gerdes.
* Update to GRASS 5.7 Radim Blazek.
*
* PURPOSE: Lower level functions for reading/writing/manipulating vectors.
*
* COPYRIGHT: (C) 2001 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.
*
*****************************************************************************/
/*
* functions - calc_begin_angle(), and calc_end_angle()
* used to calculate the angle of a line to a node.
* returns - (float)angle (-PI ... +PI)
* returns - (float)(-9) if only 1 point or more points but identical
*/
#include <stdio.h>
#include <math.h>
#include "Vect.h"
static double d_atan2 (double, double);
float
dig_calc_begin_angle (
struct line_pnts *points,
double thresh)
{
double last_x;
double last_y;
double *xptr;
double *yptr;
int short_line;
int i;
int n_points;
double *xarray;
double *yarray;
/* temporary way to set up use of struct line_pnts */
n_points = points->n_points;
xarray = points->x;
yarray = points->y;
last_x = *xarray;
last_y = *yarray;
xptr = xarray + 1;
yptr = yarray + 1;
/* check degenerate line */
if ( dig_line_degenerate ( points ) > 0 )
return ((float) -9.);
short_line = 1;
if (n_points != 2) {
/* Search for next different coord. Note that in >= g5.7, threshold
* is not used for build process. */
/* 4.1 but do not use opposite node if there are other points */
for (i = 1; i < n_points - 1; i++) {
if ((thresh < fabs (*xptr - last_x)) || (thresh < fabs (*yptr - last_y))) {
short_line = 0;
break;
}
xptr++;
yptr++;
}
}
if (short_line) {
/* for 4.1 change this to take 1st point after node -dpg 12/92 */
/* return ((float) d_atan2 (yarray[n_points - 1] - last_y, xarray[n_points - 1] - last_x)); */
return ((float) d_atan2 (yarray[1] - last_y, xarray[1] - last_x));
}
return ((float) d_atan2 (*yptr - last_y, *xptr - last_x));
} /* calc_begin_angle() */
float
dig_calc_end_angle (struct line_pnts *points, double thresh)
{
double last_x;
double last_y;
double *xptr;
double *yptr;
int short_line;
int i;
int n_points;
double *xarray;
double *yarray;
short_line = 1;
xarray = points->x;
yarray = points->y;
n_points = points->n_points;
/* check degenerate line */
if ( dig_line_degenerate ( points ) > 0 )
return ((float) -9.);
last_x = *(xarray + n_points - 1);
last_y = *(yarray + n_points - 1);
xptr = xarray + n_points - 2;
yptr = yarray + n_points - 2;
if (n_points != 2)
{
/* Search for next different coord. Note that in >= g5.7, threshold
* is not used for build process. */
/* 4.1 but do not use opposite node if there are other points */
for (i = n_points - 2; i > 0; i--) {
if ((thresh < fabs (*xptr - last_x)) || (thresh < fabs (*yptr - last_y))) {
short_line = 0;
break;
}
xptr--;
yptr--;
}
}
if (short_line) {
/* updated for 4.1 to take next point away from node -dpg */
/* return ((float) d_atan2 (yarray[0] - last_y, xarray[0] - last_x)); */
return ((float) d_atan2 (yarray[n_points - 2] - last_y, xarray[n_points - 2] - last_x));
}
return ((float) d_atan2 (*yptr - last_y, *xptr - last_x));
}
int
dig_is_line_degenerate (struct line_pnts *points, double thresh)
{
double last_x;
double last_y;
double *xptr;
double *yptr;
int short_line;
int i;
int n_points;
double *xarray;
double *yarray;
/* temporary way to set up use of struct line_pnts */
n_points = points->n_points;
xarray = points->x;
yarray = points->y;
last_x = *xarray;
last_y = *yarray;
xptr = xarray + 1;
yptr = yarray + 1;
short_line = 1;
for (i = 1; i < n_points; i++) /* Search for next different coord */
{
if ((thresh < fabs (*xptr - last_x)) ||
(thresh < fabs (*yptr - last_y)))
{
short_line = 0;
break;
}
xptr++;
yptr++;
}
if (short_line)
return (1);
return (0);
}
/* Check if line is degenerate (one point or more identical points)
* Returns: 0 is not degenerate (but som points may be identical)
* 1 one point
* 2 more identical points
*/
int
dig_line_degenerate ( struct line_pnts *points)
{
int i, ident;
int n_points;
G_debug ( 5, "dig_line_degenerate()" );
/* temporary way to set up use of struct line_pnts */
n_points = points->n_points;
if ( n_points == 1 ) {
G_debug ( 5, " Line is degenerate (one points)" );
return 1;
}
/* check identical points (= one point) */
ident = 1;
for ( i = 1 ; i < n_points; i++ ) {
if ( points->x[i] != points->x[i-1] || points->y[i] != points->y[i-1] ) {
ident = 0;
break;
}
}
if ( ident ) {
G_debug ( 5, " Line is degenerate (more points)" );
return 2;
}
return 0;
}
static double
d_atan2 (double y, double x)
{
if (y == 0.0 && x == 0.0)
return (0.0);
else
return (atan2 (y, x));
}
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