GRASS GIS 8 Programmer's Manual
8.2.2dev(2023)5c00b4e944

Vector library  intersection. More...
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <math.h>
#include <grass/vector.h>
#include <grass/rbtree.h>
#include <grass/glocale.h>
Go to the source code of this file.
Macros  
#define  QEVT_IN 1 
#define  QEVT_OUT 2 
#define  QEVT_CRS 3 
#define  GET_PARENT(p, c) ((p) = (int) (((c)  2) / 3 + 1)) 
#define  GET_CHILD(c, p) ((c) = (int) (((p) * 3)  1)) 
Functions  
int  line_check_intersection2 (struct line_pnts *APoints, struct line_pnts *BPoints, int with_z, int all) 
int  Vect_line_intersection2 (struct line_pnts *APoints, struct line_pnts *BPoints, struct bound_box *pABox, struct bound_box *pBBox, struct line_pnts ***ALines, struct line_pnts ***BLines, int *nalines, int *nblines, int with_z) 
Intersect 2 lines. More...  
int  Vect_line_check_intersection2 (struct line_pnts *APoints, struct line_pnts *BPoints, int with_z) 
Check if 2 lines intersect. More...  
int  Vect_line_get_intersections2 (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) 20012014, 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 intersect2.c.
#define GET_CHILD  (  c,  
p  
)  ((c) = (int) (((p) * 3)  1)) 
Definition at line 356 of file intersect2.c.
#define GET_PARENT  (  p,  
c  
)  ((p) = (int) (((c)  2) / 3 + 1)) 
Definition at line 355 of file intersect2.c.
#define QEVT_CRS 3 
Definition at line 353 of file intersect2.c.
#define QEVT_IN 1 
Definition at line 351 of file intersect2.c.
#define QEVT_OUT 2 
Definition at line 352 of file intersect2.c.
int line_check_intersection2  (  struct line_pnts *  APoints, 
struct line_pnts *  BPoints,  
int  with_z,  
int  all  
) 
Definition at line 1279 of file intersect2.c.
Referenced by Vect_line_check_intersection2().
int Vect_line_check_intersection2  (  struct line_pnts *  APoints, 
struct line_pnts *  BPoints,  
int  with_z  
) 
Check if 2 lines intersect.
Points (Points>n_points == 1) are also supported.
simplified Bentley–Ottmann Algorithm: similar to Vect_line_check_intersection(), but faster
APoints  first input line 
BPoints  second input line 
with_z  3D, not supported (only if one or both are points)! 
Definition at line 1560 of file intersect2.c.
References line_check_intersection2().
int Vect_line_get_intersections2  (  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_intersection2() function.
simplified Bentley–Ottmann Algorithm: similar to Vect_line_get_intersections(), but faster
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 1583 of file intersect2.c.
int Vect_line_intersection2  (  struct line_pnts *  APoints, 
struct line_pnts *  BPoints,  
struct bound_box *  pABox,  
struct bound_box *  pBBox,  
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. If B line is NULL, A line is intersected with itself.
simplified Bentley–Ottmann Algorithm: similar to Vect_line_intersection(), but faster additionally, selfintersections of a line are handled more efficiently
APoints  first input line  
BPoints  second input line or NULL  
[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 686 of file intersect2.c.
References l.