GRASS 8 Programmer's Manual
8.6.0dev(2026)-f6f2c534ea
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inside.c
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/*****************************************************************************
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*
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* MODULE: Vector library
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*
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* AUTHOR(S): Original author CERL, probably Dave Gerdes.
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* Update to GRASS 5.7 Radim Blazek.
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*
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* PURPOSE: Lower level functions for reading/writing/manipulating vectors.
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*
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* COPYRIGHT: (C) 2001 by the GRASS Development Team
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*
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* This program is free software under the GNU General Public
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* License (>=v2). Read the file COPYING that comes with GRASS
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* for details.
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*
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*****************************************************************************/
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#include <
grass/vector.h
>
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double
dig_x_intersect
(
double
beg_x
,
double
end_x
,
double
beg_y
,
double
end_y
,
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double
Y
)
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{
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double
b
;
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/* assumes beg_y != end_y */
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/* sort for numerical stability */
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if
(
end_x
<
beg_x
|| (
end_x
==
beg_x
&&
end_y
<
beg_y
)) {
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b
=
end_x
;
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end_x
=
beg_x
;
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beg_x
=
b
;
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b
=
end_y
;
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end_y
=
beg_y
;
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beg_y
=
b
;
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}
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/* solve simple linear equation to get X = a + b * Y
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* with
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* b = (end_x - beg_x) / (end_y - beg_y)
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* a = beg_x - b * beg_y
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*
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* simplify a + b * Y:
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* a + b * Y = beg_x - b * beg_y + b * Y
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* a + b * Y = beg_x + b * (Y - beg_y) */
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b
= (
end_x
-
beg_x
) / (
end_y
-
beg_y
);
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return
beg_x
+
b
* (
Y
-
beg_y
);
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}
AMI_STREAM
Definition
ami_stream.h:153
dig_x_intersect
double dig_x_intersect(double beg_x, double end_x, double beg_y, double end_y, double Y)
Definition
inside.c:20
Y
#define Y
Definition
ogsf.h:141
b
double b
Definition
r_raster.c:39
vector.h
lib
vector
diglib
inside.c
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