GIS Library - Area calculation functions. More...

#include <grass/gis.h>

Include dependency graph for gis/area.c:

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.

Detailed Description

GIS Library - Area calculation functions.

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

Definition in file gis/area.c.

Function Documentation

◆ G_area_of_cell_at_row()

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.

Parameters

row	row number

Returns: cell area

Definition at line 86 of file gis/area.c.

References PROJECTION_LL.

Referenced by N_init_geom_data_2d().

◆ G_area_of_polygon()

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.

Parameters

x	array of x coordinates
y	array of y coordinates
n	number of x,y coordinate pairs

Returns: area in square meters of the polygon

Definition at line 158 of file gis/area.c.

References G_ellipsoid_polygon_area(), G_planimetric_polygon_area(), PROJECTION_LL, and x.

Referenced by Vect_find_island(), and Vect_get_area_area().

◆ G_begin_cell_area_calculations()

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 initializations 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.

Returns: 0 if the projection is not measurable (ie. imagery or xy); 1 if the projection is planimetric (ie. UTM or SP); 2 if the projection is non-planimetric (ie. latitude-longitude)

Definition at line 45 of file gis/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(), G_get_set_window(), and PROJECTION_LL.

Referenced by N_init_geom_data_2d().

◆ G_begin_polygon_area_calculations()

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.

Returns: 0 if the projection is not measurable (ie. imagery or xy); 1 if the projection is planimetric (ie. UTM or SP); 2 if the projection is non-planimetric (ie. latitude-longitude)

Definition at line 119 of file gis/area.c.

References G_begin_ellipsoid_polygon_area(), G_database_units_to_meters_factor(), G_get_ellipsoid_parameters(), G_projection(), and PROJECTION_LL.