GRASS GIS 8 Programmer's Manual  8.4.0dev(2024)-6da4f45b8e
vector/Vlib/intersect.c File Reference

Vector library - intersection. More...

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <math.h>
#include <grass/vector.h>
#include <grass/glocale.h>
Include dependency graph for vector/Vlib/intersect.c:

Go to the source code of this file.

Macros

#define D   ((ax2 - ax1) * (by1 - by2) - (ay2 - ay1) * (bx1 - bx2))
 
#define D1   ((bx1 - ax1) * (by1 - by2) - (by1 - ay1) * (bx1 - bx2))
 
#define D2   ((ax2 - ax1) * (by1 - ay1) - (ay2 - ay1) * (bx1 - ax1))
 

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 UNUSED)
 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...
 

Detailed Description

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:

(ax2-ax1)r1 - (bx2-bx1)r2 = ax2 - ax1 (ay2-ay1)r1 - (by2-by1)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 breaks: 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) 2001-2009, 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.

Author
Original author CERL, probably Dave Gerdes or Mike Higgins.
Update to GRASS 5.7 Radim Blazek.

Definition in file vector/Vlib/intersect.c.

Macro Definition Documentation

◆ D

#define D   ((ax2 - ax1) * (by1 - by2) - (ay2 - ay1) * (bx1 - bx2))

Definition at line 91 of file vector/Vlib/intersect.c.

◆ D1

#define D1   ((bx1 - ax1) * (by1 - by2) - (by1 - ay1) * (bx1 - bx2))

Definition at line 92 of file vector/Vlib/intersect.c.

◆ D2

#define D2   ((ax2 - ax1) * (by1 - ay1) - (ay2 - ay1) * (bx1 - ax1))

Definition at line 93 of file vector/Vlib/intersect.c.

Function Documentation

◆ line_check_intersection()

int line_check_intersection ( struct line_pnts APoints,
struct line_pnts BPoints,
int  with_z 
)

Definition at line 1276 of file vector/Vlib/intersect.c.

References RTree_Rect::boundary, and G_malloc.

◆ Vect_line_check_intersection()

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

Parameters
APointsfirst input line
BPointssecond input line
with_z3D, not supported (only if one or both are points)!
Returns
0 no intersection
1 intersection found

Definition at line 1466 of file vector/Vlib/intersect.c.

◆ Vect_line_get_intersections()

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

Parameters
APointsfirst input line
BPointssecond input line
[out]IPointsoutput with intersection points
with_z3D, not supported (only if one or both are points)!
Returns
0 no intersection
1 intersection found

Definition at line 1489 of file vector/Vlib/intersect.c.

◆ Vect_line_intersection()

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  UNUSED 
)

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

Parameters
APointsfirst input line
BPointssecond input line
[out]ALinesarray of new lines created from original A line
[out]BLinesarray of new lines created from original B line
[out]nalinesnumber of new lines (ALines)
[out]nblinesnumber of new lines (BLines)
with_z3D, not supported!
Returns
0 no intersection
1 intersection found

Definition at line 660 of file vector/Vlib/intersect.c.

References l, x, and line_pnts::y.

◆ Vect_segment_intersection()

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.

Parameters
ax1,ay1,az1,ax2,ay2,az2input line a
bx1,by1,bz1,bx2,by2,bz2input line b
[out]x1,y1,z1intersection point1 (case 2-4)
[out]x2,y2,z2intersection point2 (case 2-4)
with_zuse z coordinate (3D) (TODO)
Returns
0 - do not intersect,
1 - intersect at one point,
2 - partial overlap,
3 - a contains b,
4 - b contains a,
5 - identical

Definition at line 111 of file vector/Vlib/intersect.c.