area.h File Reference

Structs and interfaces for area calculations. More...

#include "yac_types.h"
#include "clipping.h"

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Macros
#define	YAC_AREA_TOL   ((0.02 * 0.02) / (6371.2290 * 6371.2290))

Functions
double	yac_grid_cell_area (struct yac_grid_cell cell)
	Area calculation of a spherical cell.
double	yac_grid_cell_area_info (struct yac_grid_cell cell, double *barycenter, double sign)

Detailed Description

Structs and interfaces for area calculations.

Definition in file area.h.

Macro Definition Documentation

YAC_AREA_TOL

#define YAC_AREA_TOL   ((0.02 * 0.02) / (6371.2290 * 6371.2290))

an area of 20m x 20m on the Earth Surface is equivalent to an area on the unit sphere:

Definition at line 18 of file area.h.

Function Documentation

yac_grid_cell_area()

double yac_grid_cell_area

(

struct yac_grid_cell

cell

)

Area calculation of a spherical cell.

The cell in split up into triangles that all have one corner in common, then the area for each of the triangles is computed and summed up to build the area of the cell.

Compute the area of a grid cell on the unit sphere

This function computes the area of a spherical polygon that may contain both great circle edges and latitude circle edges. The polygon is triangulated using a fan triangulation from the first vertex. By summation of the signed areas of the triangles this routine is able to handle convex and concave cells. For latitude circle edges, a signed correction term is added to account for the difference between the great circle path and the latitude circle path.

Parameters

[in]

cell

Grid cell structure

Returns

The unsigned area of the grid cell on the unit sphere

Remarks

For triangles with only great circle edges, uses tri_area directly

For polygons or cells with latitude edges, uses triangulation with corrections

Returns 0.0 for degenerate cells with fewer than 2 corners

The result is always non-negative (absolute value of signed area)

Definition at line 271 of file area.c.

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yac_grid_cell_area_info()

double yac_grid_cell_area_info	(	struct yac_grid_cell	cell,
		double *	barycenter,
		double	sign )

Compute the signed area of a grid cell and update barycenter

This function computes the signed area of a spherical polygon that may contain both great circle edges and latitude circle edges. It simultaneously updates a barycenter accumulator that can be used to compute the cell's center of mass. The polygon is triangulated using a fan triangulation from the first vertex, and the signed areas of the triangles are summed to correctly handle concave cells. For latitude circle edges, correction terms are added to account for the difference between the great circle path and the latitude circle path.

Parameters

[in]	cell	Grid cell structure
[in,out]	barycenter	Barycenter accumulator to be updated (3D vector)
[in]	sign	Sign multiplier for both area and barycenter contributions

Returns

The signed area of the grid cell on the unit sphere multiplied by sign parameter

Remarks

For triangles with only great circle edges, uses tri_area_info directly

For polygons or cells with latitude edges, uses triangulation with corrections

Returns 0.0 for degenerate cells with fewer than 2 corners

The barycenter is accumulated but not normalized by this function

The sign parameter allows for proper handling of overlapping regions in conservative remapping algorithms

Definition at line 403 of file area.c.

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