YAC: src/core/clipping.c File Reference

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#include "config.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include "geometry.h"
#include "clipping.h"
#include "area.h"
#include "ensure_array_size.h"
#include "utils_core.h"

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Data Structures
struct	point_list_element

struct	point_list

Functions
static void	init_point_list (struct point_list *list)

static void	reset_point_list (struct point_list *list)

static size_t	generate_point_list (struct point_list list, struct yac_grid_cell cell, int cell_ordering, struct yac_circle circle_buffer)

static struct point_list_element *	get_free_point_list_element (struct point_list *list)

static size_t	remove_points (struct point_list *list)

static size_t	remove_zero_length_edges (struct point_list *list)
	returns number of edges/corners

static void	free_point_list (struct point_list *list)

static int	get_cell_points_ordering (struct yac_grid_cell cell)

static void	generate_cell (struct point_list list, struct yac_grid_cell cell)

static enum yac_cell_type	get_cell_type (struct yac_grid_cell target_cell)

static struct yac_grid_cell *	get_overlap_cell_buffer (size_t N)

void	yac_compute_overlap_buf_free ()

static double	get_edge_direction (double ref_corner, double corner_a, double *corner_b)

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.

static double	dotproduct (double a[], double b[])

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.

int	yac_circle_compare (void const a, void const b)

static void	compute_norm_vector_kahan (double const a[3], double const b[3], double norm_vector[3])

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

static struct yac_circle	generate_lat_circle (double z, int north_is_out)

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)

int	yac_circle_contains_north_pole (struct yac_circle *circle)

static void	circle_clipping (struct point_list cell, size_t num_cell_edges, struct yac_circle *clipping_circles, size_t num_clipping_circles)

static void	point_list_clipping (struct point_list *source_list, struct point_list target_list, size_t nct)

static void	copy_point_list (struct point_list in, struct point_list *out)

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

static void	yac_lon_lat_cell_lat_clipping (struct yac_grid_cell cell, double z_upper_bound, double z_lower_bound, struct yac_grid_cell overlap_buffer)

static double	get_closest_pole (struct point_list *cell_list)

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_correct_weights (size_t nSourceCells, double *weight)
	correct interpolation weights

static void	compute_norm_vector (double a[], double b[], double norm[])

static int	is_empty_gc_cell (struct point_list *list, size_t num_edges)

static enum yac_edge_type	circle2edge_type (enum yac_circle_type type)

Variables
static double const	tol = 1.0e-12

static struct yac_grid_cell *	overlap_cell_buffer = NULL

static size_t	overlap_cell_buffer_size = 0

Function Documentation

◆ circle2edge_type()

static enum yac_edge_type circle2edge_type ( enum yac_circle_type type )

inlinestatic

Definition at line 1751 of file clipping.c.

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◆ circle_clipping()

static void circle_clipping	(	struct point_list *	cell,
		size_t	num_cell_edges,
		struct yac_circle **	clipping_circles,
		size_t	num_clipping_circles )

static

cell clipping using Sutherland-Hodgman algorithm;

Definition at line 586 of file clipping.c.

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◆ compute_norm_vector()

static void compute_norm_vector	(	double	a[],
		double	b[],
		double	norm[] )

static

Definition at line 1709 of file clipping.c.

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◆ compute_norm_vector_kahan()

static void compute_norm_vector_kahan	(	double const	a[3],
		double const	b[3],
		double	norm_vector[3] )

static

Definition at line 402 of file clipping.c.

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◆ copy_point_list()

static void copy_point_list	(	struct point_list	in,
		struct point_list *	out )

static

Definition at line 1065 of file clipping.c.

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◆ dotproduct()

static double dotproduct	(	double	a[],
		double	b[] )

inlinestatic

Definition at line 269 of file clipping.c.

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◆ free_point_list()

static void free_point_list ( struct point_list * list )

static

Definition at line 1687 of file clipping.c.

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◆ generate_cell()

static void generate_cell	(	struct point_list *	list,
		struct yac_grid_cell *	cell )

static

Examples: test_partial_areas.c.

Definition at line 1760 of file clipping.c.

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◆ generate_lat_circle()

static struct yac_circle generate_lat_circle	(	double	z,
		int	north_is_out )

inlinestatic

Definition at line 461 of file clipping.c.

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◆ generate_point_list()

static size_t generate_point_list	(	struct point_list *	list,
		struct yac_grid_cell	cell,
		int	cell_ordering,
		struct yac_circle *	circle_buffer )

static

Definition at line 1627 of file clipping.c.

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◆ get_cell_points_ordering()

static int get_cell_points_ordering ( struct yac_grid_cell cell )

static

Definition at line 1468 of file clipping.c.

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◆ get_cell_type()

static enum yac_cell_type get_cell_type ( struct yac_grid_cell target_cell )

static

Definition at line 287 of file clipping.c.

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◆ get_closest_pole()

static double get_closest_pole ( struct point_list * cell_list )

static

Definition at line 1306 of file clipping.c.

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◆ get_edge_direction()

static double get_edge_direction	(	double *	ref_corner,
		double *	corner_a,
		double *	corner_b )

static

Definition at line 99 of file clipping.c.

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◆ get_free_point_list_element()

static struct point_list_element * get_free_point_list_element ( struct point_list * list )

static

Definition at line 1659 of file clipping.c.

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◆ get_overlap_cell_buffer()

static struct yac_grid_cell * get_overlap_cell_buffer ( size_t N )

inlinestatic

Definition at line 69 of file clipping.c.

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◆ init_point_list()

static void init_point_list ( struct point_list * list )

static

Definition at line 1523 of file clipping.c.

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◆ is_empty_gc_cell()

static int is_empty_gc_cell	(	struct point_list *	list,
		size_t	num_edges )

static

Definition at line 1720 of file clipping.c.

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◆ point_list_clipping()

static void point_list_clipping	(	struct point_list *	source_list,
		struct point_list	target_list,
		size_t	nct )

static

Definition at line 1042 of file clipping.c.

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◆ remove_points()

static size_t remove_points ( struct point_list * list )

static

Definition at line 1541 of file clipping.c.

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◆ remove_zero_length_edges()

static size_t remove_zero_length_edges ( struct point_list * list )

static

returns number of edges/corners

Definition at line 1597 of file clipping.c.

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◆ reset_point_list()

static void reset_point_list ( struct point_list * list )

static

Definition at line 1529 of file clipping.c.

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◆ 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)

Examples: test_area.c, test_clipping.c, and test_compute_overlap_area.c.

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

Examples: test_lat_clipping.c.

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)

Examples: test_circle.c.

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

Examples: test_circle.c.

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

Examples: test_circle.c.

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

Examples: test_circle.c.

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

Examples: test_circle.c.

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

Examples: test_compute_overlap_area.c, and test_partial_areas.c.

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

Examples: test_compute_overlap_area.c, and test_partial_areas.c.

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.

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

Examples: test_compute_overlap_area.c, and test_partial_areas.c.

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

Examples: test_clipping.c, test_interp_method_avg_parallel.c, and test_partial_areas.c.

Definition at line 1447 of file clipping.c.

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◆ yac_lon_lat_cell_lat_clipping()

static void yac_lon_lat_cell_lat_clipping	(	struct yac_grid_cell *	cell,
		double	z_upper_bound,
		double	z_lower_bound,
		struct yac_grid_cell *	overlap_buffer )

static

Definition at line 1197 of file clipping.c.

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Variable Documentation

◆ overlap_cell_buffer

struct yac_grid_cell* overlap_cell_buffer = NULL

static

Definition at line 66 of file clipping.c.

◆ overlap_cell_buffer_size

size_t overlap_cell_buffer_size = 0

static

Definition at line 67 of file clipping.c.

◆ tol

double const tol = 1.0e-12

static

Definition at line 23 of file clipping.c.

Data Structures

Functions

Variables

Function Documentation

◆ circle2edge_type()

◆ circle_clipping()

◆ compute_norm_vector()

◆ compute_norm_vector_kahan()

◆ copy_point_list()

◆ dotproduct()

◆ free_point_list()

◆ generate_cell()

◆ generate_lat_circle()

◆ generate_point_list()

◆ get_cell_points_ordering()

◆ get_cell_type()

◆ get_closest_pole()

◆ get_edge_direction()

◆ get_free_point_list_element()

◆ get_overlap_cell_buffer()

◆ init_point_list()

◆ is_empty_gc_cell()

◆ point_list_clipping()

◆ remove_points()

◆ remove_zero_length_edges()

◆ reset_point_list()

◆ yac_cell_clipping()

◆ yac_cell_lat_clipping()

◆ yac_circle_compare()

◆ yac_circle_compare_distances()

◆ yac_circle_contains_north_pole()

◆ yac_circle_generate()

◆ yac_circle_point_is_inside()

◆ yac_compute_overlap_areas()

◆ yac_compute_overlap_buf_free()

◆ yac_compute_overlap_info()

◆ yac_correct_weights()

◆ yac_lon_lat_cell_lat_clipping()

Variable Documentation

◆ overlap_cell_buffer

◆ overlap_cell_buffer_size

◆ tol