align_window.c

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/*!
 * \file lib/raster/align_window.c
 *
 * \brief GIS Library - Window alignment functions.
 *
 * (C) 2001-2009 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 Original author CERL
 */

#include <stdio.h>
#include <math.h>

#include <grass/gis.h>
#include <grass/raster.h>

/*!
 * \brief Align two regions.
 *
 * Modifies the input <i>window</i> to align to <i>ref</i> region. The
 * resolutions in <i>window</i> are set to match those in <i>ref</i>
 * and the <i>window</i> edges (north, south, east, west) are modified
 * to align with the grid of the <i>ref</i> region.
 *
 * The <i>window</i> 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 pointer to Cell_head to be modified
 * \param ref pointer to Cell_head
 *
 * \return NULL on success
 */

void Rast_align_window(struct Cell_head *window, const struct Cell_head *ref)
{
    G_debug(1, "Rast_align_window()");

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

    G_debug(1, "before alignment:");
    G_debug(1, "North: %.15g", window->north);
    G_debug(1, "South: %.15g", window->south);
    G_debug(1, "West: %.15g", window->west);
    G_debug(1, "East: %.15g", window->east);

    window->north =
        ref->north - floor((ref->north - window->north) / ref->ns_res) * ref->ns_res;
    window->south =
        ref->south - ceil((ref->south - window->south) / ref->ns_res) * ref->ns_res;
    /* Rast_easting_to_col() wraps easting:
     * east can become < west, or both west and east are shifted */
    window->west =
        ref->west + floor((window->west - ref->west) / ref->ew_res) * ref->ew_res;
    window->east =
        ref->east + ceil((window->east - ref->east) / ref->ew_res) * ref->ew_res;

    if (window->proj == PROJECTION_LL) {
        while (window->north > 90.0 + window->ns_res / 2.0)
            window->north -= window->ns_res;
        while (window->south < -90.0 - window->ns_res / 2.0)
            window->south += window->ns_res;
    }

    G_debug(1, "after alignment:");
    G_debug(1, "North: %.15g", window->north);
    G_debug(1, "South: %.15g", window->south);
    G_debug(1, "West: %.15g", window->west);
    G_debug(1, "East: %.15g", window->east);

    G_adjust_Cell_head(window, 0, 0);
}