GRASS GIS 8 Programmer's Manual  8.4.0dev(2024)-c17eaff561
intersect2.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/rbtree.h>
#include <grass/glocale.h>
Include dependency graph for intersect2.c:

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...
 

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) 2001-2014, 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.
Update to GRASS 7 Markus Metz.

Definition in file intersect2.c.

Macro Definition Documentation

◆ GET_CHILD

#define GET_CHILD (   c,
 
)    ((c) = (int)(((p)*3) - 1))

Definition at line 347 of file intersect2.c.

◆ GET_PARENT

#define GET_PARENT (   p,
 
)    ((p) = (int)(((c)-2) / 3 + 1))

Definition at line 346 of file intersect2.c.

◆ QEVT_CRS

#define QEVT_CRS   3

Definition at line 344 of file intersect2.c.

◆ QEVT_IN

#define QEVT_IN   1

Definition at line 342 of file intersect2.c.

◆ QEVT_OUT

#define QEVT_OUT   2

Definition at line 343 of file intersect2.c.

Function Documentation

◆ line_check_intersection2()

int line_check_intersection2 ( struct line_pnts APoints,
struct line_pnts BPoints,
int  with_z,
int  all 
)

Definition at line 1260 of file intersect2.c.

Referenced by Vect_line_check_intersection2().

◆ 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

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

Definition at line 1540 of file intersect2.c.

References line_check_intersection2().

◆ Vect_line_get_intersections2()

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

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 1562 of file intersect2.c.

◆ Vect_line_intersection2()

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, self-intersections of a line are handled more efficiently

Parameters
APointsfirst input line
BPointssecond input line or NULL
[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 675 of file intersect2.c.

References l.