Geografic-Information-System/lib/gis/align_window.c

/**
 * \file align_window.c
 *
 * \brief GIS Library - Window alignment functions.
 *
 * (C) 2001-2008 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.
 *
 * \author GRASS GIS Development Team
 *
 * \date 1999-2008
 */

#include <stdio.h>
#include <math.h>
#include <grass/gis.h>


/**
 * \brief Align two regions.
 *
 * Modifies the input <b>window</b> to align to
 * <b>ref</b> region. The resolutions in <b>window</b> are set to match those
 * in <b>ref</b> and the <b>window</b> edges (north, south, east, west) are
 * modified to align with the grid of the <b>ref</b> region.
 * The <b>window</b> may be enlarged if necessary to achieve the alignment.
 * The north is rounded northward, the south southward, the east eastward and the
 * west westward. Lon-lon constraints are taken into consideration
 * to make sure that the north doesn't go above 90 degrees (for lat/lon)
 * or that the east does "wrap" past the west, etc.
 *
 * \param[in,out] window
 * \param[in] ref
 * \return NULL on success
 * \return Pointer to an error string on failure
 */

char *G_align_window(struct Cell_head *window, const struct Cell_head *ref)
{
    int preserve;

    window->ns_res = ref->ns_res;
    window->ew_res = ref->ew_res;
    window->zone = ref->zone;
    window->proj = ref->proj;

    preserve = window->proj == PROJECTION_LL &&
	window->east == (window->west + 360);
    window->south =
	G_row_to_northing(ceil(G_northing_to_row(window->south, ref)), ref);
    window->north =
	G_row_to_northing(floor(G_northing_to_row(window->north, ref)), ref);
    window->east =
	G_col_to_easting(ceil(G_easting_to_col(window->east, ref)), ref);
    window->west =
	G_col_to_easting(floor(G_easting_to_col(window->west, ref)), ref);

    if (window->proj == PROJECTION_LL) {
	while (window->north > 90.0)
	    window->north -= window->ns_res;
	while (window->south < -90.0)
	    window->south += window->ns_res;

	if (preserve)
	    window->east = window->west + 360;
	else
	    while (window->east - window->west > 360.0)
		window->east -= window->ew_res;
    }

    return G_adjust_Cell_head(window, 0, 0);
}