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/*!
\file remove_areas.c
\brief Vector library - clean geometry (remove small areas)
Higher level functions for reading/writing/manipulating vectors.
(C) 2001-2008 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 Radim Blazek
\date 2001
*/
#include <stdlib.h>
#include <grass/gis.h>
#include <grass/Vect.h>
#include <grass/glocale.h>
/*!
\brief Remove small areas from the map map.
Centroid of the area and the longest boundary
with adjacent area is removed.
Map topology must be built GV_BUILD_CENTROIDS.
\param Map vector map
\param thresh maximum area size for removed areas
\param Err vector map where removed lines and centroids are written
\param removed_area pointer to where total size of removed area is stored or NULL
\return number of removed areas
*/
int
Vect_remove_small_areas(struct Map_info *Map, double thresh,
struct Map_info *Err, double *removed_area)
{
int area, nareas;
int nremoved = 0;
struct ilist *List;
struct ilist *AList;
struct line_pnts *Points;
struct line_cats *Cats;
double size_removed = 0.0;
List = Vect_new_list();
AList = Vect_new_list();
Points = Vect_new_line_struct();
Cats = Vect_new_cats_struct();
nareas = Vect_get_num_areas(Map);
for (area = 1; area <= nareas; area++) {
int i, j, centroid, dissolve_neighbour;
double length, size;
G_percent(area, nareas, 1);
G_debug(3, "area = %d", area);
if (!Vect_area_alive(Map, area))
continue;
size = Vect_get_area_area(Map, area);
if (size > thresh)
continue;
size_removed += size;
/* The area is smaller than the limit -> remove */
/* Remove centroid */
centroid = Vect_get_area_centroid(Map, area);
if (centroid > 0) {
if (Err) {
Vect_read_line(Map, Points, Cats, centroid);
Vect_write_line(Err, GV_CENTROID, Points, Cats);
}
Vect_delete_line(Map, centroid);
}
/* Find the adjacent area with which the longest boundary is shared */
Vect_get_area_boundaries(Map, area, List);
/* Create a list of neighbour areas */
Vect_reset_list(AList);
for (i = 0; i < List->n_values; i++) {
int line, left, right, neighbour;
line = List->value[i];
if (!Vect_line_alive(Map, abs(line))) /* Should not happen */
G_fatal_error(_("Area is composed of dead boundary"));
Vect_get_line_areas(Map, abs(line), &left, &right);
if (line > 0)
neighbour = left;
else
neighbour = right;
G_debug(4, " line = %d left = %d right = %d neighbour = %d",
line, left, right, neighbour);
Vect_list_append(AList, neighbour); /* this checks for duplicity */
}
G_debug(3, "num neighbours = %d", AList->n_values);
/* Go through the list of neghours and find that with the longest boundary */
dissolve_neighbour = 0;
length = -1.0;
for (i = 0; i < AList->n_values; i++) {
int neighbour1;
double l = 0.0;
neighbour1 = AList->value[i];
G_debug(4, " neighbour1 = %d", neighbour1);
for (j = 0; j < List->n_values; j++) {
int line, left, right, neighbour2;
line = List->value[j];
Vect_get_line_areas(Map, abs(line), &left, &right);
if (line > 0)
neighbour2 = left;
else
neighbour2 = right;
if (neighbour2 == neighbour1) {
Vect_read_line(Map, Points, NULL, abs(line));
l += Vect_line_length(Points);
}
}
if (l > length) {
length = l;
dissolve_neighbour = neighbour1;
}
}
G_debug(3, "dissolve_neighbour = %d", dissolve_neighbour);
/* Make list of boundaries to be removed */
Vect_reset_list(AList);
for (i = 0; i < List->n_values; i++) {
int line, left, right, neighbour;
line = List->value[i];
Vect_get_line_areas(Map, abs(line), &left, &right);
if (line > 0)
neighbour = left;
else
neighbour = right;
G_debug(3, " neighbour = %d", neighbour);
if (neighbour == dissolve_neighbour) {
Vect_list_append(AList, abs(line));
}
}
/* Remove boundaries */
for (i = 0; i < AList->n_values; i++) {
int line;
line = AList->value[i];
if (Err) {
Vect_read_line(Map, Points, Cats, line);
Vect_write_line(Err, GV_BOUNDARY, Points, Cats);
}
Vect_delete_line(Map, line);
}
nremoved++;
nareas = Vect_get_num_areas(Map);
}
if (removed_area)
*removed_area = size_removed;
return (nremoved);
}
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