GRASS GIS 8 Programmer's Manual 8.4.1(2025)-45ca3179ab
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GIS Library - Area calculation functions. More...
#include <grass/gis.h>
Go to the source code of this file.
Functions | |
int | G_begin_cell_area_calculations (void) |
Begin cell area calculations. | |
double | G_area_of_cell_at_row (int row) |
Cell area in specified row. | |
int | G_begin_polygon_area_calculations (void) |
Begin polygon area calculations. | |
double | G_area_of_polygon (const double *x, const double *y, int n) |
Area in square meters of polygon. | |
GIS Library - Area calculation functions.
(C) 2001-2009 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 area.c.
double G_area_of_cell_at_row | ( | int | row | ) |
Cell area in specified row.
This routine returns the area in square meters of a cell in the specified row. This value is constant for planimetric grids and varies with the row if the projection is latitude-longitude.
row | row number |
Definition at line 87 of file area.c.
Referenced by N_init_geom_data_2d().
double G_area_of_polygon | ( | const double * | x, |
const double * | y, | ||
int | n ) |
Area in square meters of polygon.
Returns the area in square meters of the polygon described by the n pairs of x,y coordinate vertices. It is used both for planimetric and latitude-longitude projections.
You should call G_begin_polygon_area_calculations() function before calling this function.
Note: If the database is planimetric with the non-meter grid, this routine performs the required unit conversion to produce square meters.
x | array of x coordinates |
y | array of y coordinates |
n | number of x,y coordinate pairs |
Definition at line 159 of file area.c.
References G_ellipsoid_polygon_area(), G_planimetric_polygon_area(), and x.
int G_begin_cell_area_calculations | ( | void | ) |
Begin cell area calculations.
This routine must be called once before any call to G_area_of_cell_at_row(). It perform all inititalizations needed to do area calculations for grid cells, based on the current window "projection" field. It can be used in either planimetric projections or the latitude-longitude projection.
Definition at line 46 of file area.c.
References G_begin_zone_area_on_ellipsoid(), G_begin_zone_area_on_sphere(), G_darea0_on_ellipsoid(), G_darea0_on_sphere(), G_database_units_to_meters_factor(), G_get_ellipsoid_parameters(), and G_get_set_window().
Referenced by N_init_geom_data_2d().
int G_begin_polygon_area_calculations | ( | void | ) |
Begin polygon area calculations.
This initializes the polygon area calculation routines. It is used both for planimetric and latitude-longitude projections.
Definition at line 120 of file area.c.
References G_begin_ellipsoid_polygon_area(), G_database_units_to_meters_factor(), G_get_ellipsoid_parameters(), and G_projection().