clipping.h File Reference

#include "grid_cell.h"

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Functions
void	yac_cell_clipping (size_t N, struct yac_grid_cell *source_cell, struct yac_grid_cell target_cell, struct yac_grid_cell *overlap_buffer)
	cell clipping to get the cells describing the intersections
void	yac_cell_lat_clipping (size_t N, struct yac_grid_cell *cells, double lat_bounds[2], struct yac_grid_cell *overlap_buffer)
	cell clipping to get the cells describing the intersections
void	yac_compute_overlap_areas (size_t N, struct yac_grid_cell *source_cell, struct yac_grid_cell target_cell, double *partial_areas)
	calculates partial areas for all overlapping parts of the source cells with arbitrary target cells, this is required for conservative remapping.
void	yac_compute_overlap_info (size_t N, struct yac_grid_cell *source_cell, struct yac_grid_cell target_cell, double *overlap_areas, double(*overlap_barycenters)[3])
	calculates partial areas for all overlapping parts of the source cells with arbitrary target cells, this is required for conservative remapping. In addition, the barycenter of each overlap is calculated.
void	yac_compute_overlap_buf_free ()
void	yac_correct_weights (size_t N, double *weight)
	correct interpolation weights
void	yac_circle_generate (double const *a, double const *b, enum yac_edge_type type, int edge_ordering, struct yac_circle *circle)
int	yac_circle_compare (void const *a, void const *b)
int	yac_circle_contains_north_pole (struct yac_circle *circle)
int	yac_circle_point_is_inside (double const point[3], struct yac_circle *circle)
int	yac_circle_compare_distances (double const a[3], double const b[3], struct yac_circle *circle)

Function Documentation

yac_cell_clipping()

void yac_cell_clipping	(	size_t	N,
		struct yac_grid_cell *	source_cell,
		struct yac_grid_cell	target_cell,
		struct yac_grid_cell *	overlap_buffer )

cell clipping to get the cells describing the intersections

The routine takes (a list of) source cells and a target cell. It sets the target cell data and does some further initialisation. Thus it needs to be called for each new target cell intersection calculation

The vertices of source and target cells can be either provided in a clockwise or anticlockwise sense.

Parameters

[in]	N	number of source cells
[in]	source_cell	list of source cells
[in]	target_cell	target cell
[in]	overlap_buffer	buffer for the overlaps between the target and the source cells

Remarks

source cells can be either convex or concave

target cell has to be convex

cells in overlap_buffer can be concave (even if source cell was convex)

overlap_buffer must contain valid grid_cells (have to be initialised using yac_init_grid_cell; initialisation have to be done only once, in consecutive calls, the cells can be reused with have to be reinitialised)

Definition at line 1090 of file clipping.c.

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yac_cell_lat_clipping()

void yac_cell_lat_clipping	(	size_t	N,
		struct yac_grid_cell *	cells,
		double	lat_bounds[2],
		struct yac_grid_cell *	overlap_buffer )

cell clipping to get the cells describing the intersections

The routine takes (a list of) cells and two latitude bounds.

Parameters

[in]	N	number of cells
[in]	cells	list of cells
[in]	lat_bounds	latitude bounds in radiant
[in]	overlap_buffer	buffer for the overlaps between the cells and latitude band

Remarks

cells in overlap_buffer can be concave

overlap_buffer must contain valid grid_cells (have to be initialised using yac_init_grid_cell; initialisation have to be done only once, in consecutive calls, the cells can be reused with have to be reinitialised)

this routine is currently not being used within YAC but potentially used within the CDOs

Definition at line 1327 of file clipping.c.

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yac_circle_compare()

int yac_circle_compare	(	void const *	a,
		void const *	b )

Compare routine for yac circles (first by type and second parameters of the circle, if types are identical)

Parameters

[in]	a	yac circle a
[in]	b	yac circle b

Returns

-1, 0, or 1 depending on the circles (lat circles always come last)

Definition at line 344 of file clipping.c.

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yac_circle_compare_distances()

int yac_circle_compare_distances	(	double const	a[3],
		double const	b[3],
		struct yac_circle *	circle )

Compares the distances of two points to a given yac circle

Parameters

[in]	a	point a
[in]	b	point b
[in]	circle	yac circle

Returns

-1 if point a is closer to the circle than point b
0 if point a and b have the same distance to the circle
1 if point b is closer to the circle than point a

Definition at line 509 of file clipping.c.

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yac_circle_contains_north_pole()

int yac_circle_contains_north_pole

(

struct yac_circle *

circle

)

Determines whether the provided yac circle contains the north pole

Parameters

[in]

circle

yac circle

Returns

1 if the circle contains the north pole, 0 otherwise

Definition at line 563 of file clipping.c.

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yac_circle_generate()

void yac_circle_generate	(	double const *	a,
		double const *	b,
		enum yac_edge_type	type,
		int	edge_ordering,
		struct yac_circle *	circle )

Generate a yac circle

Parameters

[in]	a	point a
[in]	b	point b
[in]	type	typ of edge connecting points a and b
[in]	edge_ordering	ordering of the points a and b
[out]	circle	yac circle

Definition at line 415 of file clipping.c.

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yac_circle_point_is_inside()

int yac_circle_point_is_inside	(	double const	point[3],
		struct yac_circle *	circle )

Determines whether a given point is on the "inside"-side of a plane defined by the given yac circle

Parameters

[in]	point	point to be checked
[in]	circle	yac circle

Returns

0 if the point is not inside
1 if the point is inside
2 if the point is on the plane

Definition at line 471 of file clipping.c.

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yac_compute_overlap_areas()

void yac_compute_overlap_areas	(	size_t	N,
		struct yac_grid_cell *	source_cell,
		struct yac_grid_cell	target_cell,
		double *	partial_areas )

calculates partial areas for all overlapping parts of the source cells with arbitrary target cells, this is required for conservative remapping.

Some of the underlying concepts can be found in

See e.g. Joseph O'Rourke, Computational Geometry in C, 2nd Ed., 1998 Sec. 7.6 Intersections of Convex Polygons, page 253.

The routine takes (a list of) source cells and a target cell. It determines the clipping points of the intersection between a source and the target cells using cell_clipping internally. In a second step areas are calculated for each intersection described in the overlap cells. If a target cell is fully covered by N source cells the N partial areas should add up to the area of the target cell.

Parameters

[in]	N	number of source cells
[in]	source_cell	list of source cells
[in]	target_cell	target cell
[out]	partial_areas	list of N partial weights, one weight for each source-target intersection

Definition at line 276 of file clipping.c.

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yac_compute_overlap_buf_free()

void yac_compute_overlap_buf_free

(

)

Frees buffer allocated by yac_compute_overlap_info

Definition at line 88 of file clipping.c.

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yac_compute_overlap_info()

void yac_compute_overlap_info	(	size_t	N,
		struct yac_grid_cell *	source_cell,
		struct yac_grid_cell	target_cell,
		double *	overlap_areas,
		double(*)	overlap_barycenters[3] )

calculates partial areas for all overlapping parts of the source cells with arbitrary target cells, this is required for conservative remapping. In addition, the barycenter of each overlap is calculated.

Some of the underlying concepts can be found in

See e.g. Joseph O'Rourke, Computational Geometry in C, 2nd Ed., 1998 Sec. 7.6 Intersections of Convex Polygons, page 253.

The routine takes (a list of) source cells and a target cell. It determines the clipping points of the intersection between a source and the target cells using cell_clipping internally. In a second step areas are calculated for each intersection described in the overlap cells. If a target cell is fully covered by N source cells the N partial areas should add up to the area of the target cell.

Parameters

[in]	N	number of source cells
[in]	source_cell	list of source cells
[in]	target_cell	target cell
[out]	overlap_areas	list of N partial weights, one weight for each source-target intersection
[out]	overlap_barycenters	coordinates of the barycenters of the overlap cell

Remarks

for efficiency the overlap computation keeps an internal buffer, which can be freed by a call to yac_compute_overlap_buf_free

Definition at line 119 of file clipping.c.

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yac_correct_weights()

void yac_correct_weights	(	size_t	N,
		double *	weight )

correct interpolation weights

Returns weights with a sum close to 1.0

Parameters

[in]	N	number of source cells
[out]	weight	list of N partial weights

Definition at line 1447 of file clipping.c.

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