GRASS GIS 8 Programmer's Manual
8.2.2dev(2023)e6660eef60

Vector library  intersection. More...
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <math.h>
#include <grass/vector.h>
#include <grass/glocale.h>
Go to the source code of this file.
Macros  
#define  D ((ax2ax1)*(by1by2)  (ay2ay1)*(bx1bx2)) 
#define  D1 ((bx1ax1)*(by1by2)  (by1ay1)*(bx1bx2)) 
#define  D2 ((ax2ax1)*(by1ay1)  (ay2ay1)*(bx1ax1)) 
Functions  
int  line_check_intersection (struct line_pnts *APoints, struct line_pnts *BPoints, int with_z) 
int  Vect_segment_intersection (double ax1, double ay1, double az1, double ax2, double ay2, double az2, double bx1, double by1, double bz1, double bx2, double by2, double bz2, double *x1, double *y1, double *z1, double *x2, double *y2, double *z2, int with_z) 
Check for intersect of 2 line segments. More...  
int  Vect_line_intersection (struct line_pnts *APoints, struct line_pnts *BPoints, struct bound_box *ABox, struct bound_box *BBox, struct line_pnts ***ALines, struct line_pnts ***BLines, int *nalines, int *nblines, int with_z) 
Intersect 2 lines. More...  
int  Vect_line_check_intersection (struct line_pnts *APoints, struct line_pnts *BPoints, int with_z) 
Check if 2 lines intersect. More...  
int  Vect_line_get_intersections (struct line_pnts *APoints, struct line_pnts *BPoints, struct line_pnts *IPoints, int with_z) 
Get 2 lines intersection points. More...  
Vector library  intersection.
Higher level functions for reading/writing/manipulating vectors.
Some parts of code taken from grass50 v.spag/linecros.c
Based on the following:
(ax2ax1)r1  (bx2bx1)r2 = ax2  ax1 (ay2ay1)r1  (by2by1)r2 = ay2  ay1
Solving for r1 and r2, if r1 and r2 are between 0 and 1, then line segments (ax1,ay1)(ax2,ay2) and (bx1,by1)(bx2,by2) intersect.
Intersect 2 line segments.
Returns: 0  do not intersect 1  intersect at one point
\ / \ / \ / \/ \/ \/ /\ \ / \ \ 2  partial overlap ( \/ )  a ( distance < threshold )  b ( ) 3  a contains b ( /\ )  a  a  b  b 4  b contains a  a  a  b  b 5  identical  a  b
Intersection points:
return point1 breakes: point2 breaks: distance1 on: distance2 on: 0     1 a,b  a b 2 a b a b 3 a a a a 4 b b b b 5    
Sometimes (often) is important to get the same coordinates for a x b and b x a. To reach this, the segments a,b are 'sorted' at the beginning, so that for the same switched segments, results are identical. (reason is that double values are always rounded because of limited number of decimal places and for different order of coordinates, the results would be different)
(C) 20012009, 2022 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.
Definition in file vector/Vlib/intersect.c.
#define D ((ax2ax1)*(by1by2)  (ay2ay1)*(bx1bx2)) 
Definition at line 91 of file vector/Vlib/intersect.c.
#define D1 ((bx1ax1)*(by1by2)  (by1ay1)*(bx1bx2)) 
Definition at line 92 of file vector/Vlib/intersect.c.
#define D2 ((ax2ax1)*(by1ay1)  (ay2ay1)*(bx1ax1)) 
Definition at line 93 of file vector/Vlib/intersect.c.
Definition at line 1270 of file vector/Vlib/intersect.c.
References RTree_Rect::boundary, and G_malloc.
int Vect_line_check_intersection  (  struct line_pnts *  APoints, 
struct line_pnts *  BPoints,  
int  with_z  
) 
Check if 2 lines intersect.
Points (Points>n_points == 1) are also supported.
Superseded by the faster Vect_line_check_intersection2() Kept as reference implementation
APoints  first input line 
BPoints  second input line 
with_z  3D, not supported (only if one or both are points)! 
Definition at line 1455 of file vector/Vlib/intersect.c.
int Vect_line_get_intersections  (  struct line_pnts *  APoints, 
struct line_pnts *  BPoints,  
struct line_pnts *  IPoints,  
int  with_z  
) 
Get 2 lines intersection points.
A wrapper around Vect_line_check_intersection() function.
Superseded by the faster Vect_line_get_intersections2() Kept as reference implementation
APoints  first input line  
BPoints  second input line  
[out]  IPoints  output with intersection points 
with_z  3D, not supported (only if one or both are points)! 
Definition at line 1479 of file vector/Vlib/intersect.c.
int Vect_line_intersection  (  struct line_pnts *  APoints, 
struct line_pnts *  BPoints,  
struct bound_box *  ABox,  
struct bound_box *  BBox,  
struct line_pnts ***  ALines,  
struct line_pnts ***  BLines,  
int *  nalines,  
int *  nblines,  
int  with_z  
) 
Intersect 2 lines.
Creates array of new lines created from original A line, by intersection with B line. Points (Points>n_points == 1) are not supported.
Superseded by the faster Vect_line_intersection2() Kept as reference implementation
APoints  first input line  
BPoints  second input line  
[out]  ALines  array of new lines created from original A line 
[out]  BLines  array of new lines created from original B line 
[out]  nalines  number of new lines (ALines) 
[out]  nblines  number of new lines (BLines) 
with_z  3D, not supported! 
Definition at line 655 of file vector/Vlib/intersect.c.
References l, x, and line_pnts::y.
int Vect_segment_intersection  (  double  ax1, 
double  ay1,  
double  az1,  
double  ax2,  
double  ay2,  
double  az2,  
double  bx1,  
double  by1,  
double  bz1,  
double  bx2,  
double  by2,  
double  bz2,  
double *  x1,  
double *  y1,  
double *  z1,  
double *  x2,  
double *  y2,  
double *  z2,  
int  with_z  
) 
Check for intersect of 2 line segments.
ax1,ay1,az1,ax2,ay2,az2  input line a  
bx1,by1,bz1,bx2,by2,bz2  input line b  
[out]  x1,y1,z1  intersection point1 (case 24) 
[out]  x2,y2,z2  intersection point2 (case 24) 
with_z  use z coordinate (3D) (TODO) 
Definition at line 111 of file vector/Vlib/intersect.c.