GRASS GIS 8 Programmer's Manual
8.5.0dev(2024)-0824e8842e
|
GIS Library - Ellipse area routines. More...
Go to the source code of this file.
Functions | |
void | G_begin_zone_area_on_ellipsoid (double a, double e2, double s) |
Begin area calculations for ellipsoid. More... | |
double | G_darea0_on_ellipsoid (double lat) |
Calculate integral for area between two latitudes. More... | |
double | G_area_for_zone_on_ellipsoid (double north, double south) |
Calculates area between latitudes. More... | |
GIS Library - Ellipse area routines.
(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_ellipse.c.
double G_area_for_zone_on_ellipsoid | ( | double | north, |
double | south | ||
) |
Calculates area between latitudes.
This routine shows how to calculate area between two lats, but isn't efficient for row by row since G_darea0_on_ellipsoid() will be called twice for the same lat, once as a south then again as a north.
Returns the area between latitudes north and south scaled by the factor s passed to G_begin_zone_area_on_ellipsoid().
north | north coordinate |
south | south coordinate |
Definition at line 89 of file area_ellipse.c.
References G_darea0_on_ellipsoid().
void G_begin_zone_area_on_ellipsoid | ( | double | a, |
double | e2, | ||
double | s | ||
) |
Begin area calculations for ellipsoid.
Initializes raster area calculations for an ellipsoid, where a is the semi-major axis of the ellipse (in meters), e2 is the ellipsoid eccentricity squared, and s is a scale factor to allow for calculations of part of the zone (s=1.0 is full zone, s=0.5 is half the zone, and s=360/ew_res is for a single grid cell).
Note: e2 must be positive. A negative value makes no sense, and zero implies a sphere.
a | semi-major axis |
e2 | ellipsoid eccentricity |
s | scale factor |
Definition at line 47 of file area_ellipse.c.
double G_darea0_on_ellipsoid | ( | double | lat | ) |
Calculate integral for area between two latitudes.
This routine is part of the integral for the area between two latitudes.
lat | latitude |
Definition at line 63 of file area_ellipse.c.
References Radians, st, and x.
Referenced by G_area_for_zone_on_ellipsoid().