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 (double const a[], double const b[], double norm[])

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, double r, int north_is_out)

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

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

int	yac_circle_contains_north_pole (struct yac_circle const *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 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 1848 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 617 of file clipping.c.

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◆ compute_norm_vector()

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

static

Definition at line 395 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 1100 of file clipping.c.

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◆ dotproduct()

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

inlinestatic

Definition at line 264 of file clipping.c.

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◆ free_point_list()

static void free_point_list ( struct point_list * list )

static

Definition at line 1777 of file clipping.c.

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◆ generate_cell()

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

static

Definition at line 1857 of file clipping.c.

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◆ generate_lat_circle()

static struct yac_circle generate_lat_circle	(	double	z,
		double	r,
		int	north_is_out )

inlinestatic

generates a circle of latitude

Parameters

[in]	z	z coordinate of the circle of latitude
[in]	r	distance of the circle of latitude from the polar axis (has to be consistent with z)
[in]	north_is_out	if true, the north pole is outside of the circle

Definition at line 481 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 1727 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 1538 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 282 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 1365 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 1757 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 1592 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 1799 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 1079 of file clipping.c.

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◆ remove_points()

static size_t remove_points ( struct point_list * list )

static

Definition at line 1610 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 1666 of file clipping.c.

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◆ reset_point_list()

static void reset_point_list ( struct point_list * list )

static

Definition at line 1598 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; two adjacent edges of a cell that are on the same circle of latitude have to point into the same direction (a cell whose boundary goes back and forth along a circle of latitude is not supported); 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 1125 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: two adjacent edges of a cell that are on the same circle of latitude have to point into the same direction (a cell whose boundary goes back and forth along a circle of latitude is not supported); 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 1386 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

Return values

<0	if circle a orders before circle b
0	if circle a and circle b are considered equal
>0	if circle a orders after circle b

Remarks: lat circles always order after non-lat circles, regardless of their other parameters

Definition at line 339 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 const *	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

Return values

<0	if point a is closer to the circle than point b
0	if point a and b have the same distance to the circle
>0	if point b is closer to the circle than point a

Definition at line 542 of file clipping.c.

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◆ yac_circle_contains_north_pole()

int yac_circle_contains_north_pole ( struct yac_circle const * circle )

Determines whether the provided YAC circle contains the north pole

Parameters

[in] circle YAC circle

Return values

Nonzero	if the circle contains the north pole
Zero	otherwise

Definition at line 595 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 407 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 const *	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

Return values

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

Definition at line 492 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 271 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.

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

Remarks: if the weights add up to (nearly) zero, they cannot be scaled to a sum of 1.0 and are left unchanged

Definition at line 1513 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

clips a lon-lat cell with a latitude band

Remarks: the cell has to have exactly four corners (a lon-lat cell whose lat edge collapsed at a pole is not supported)

Definition at line 1245 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()

◆ 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