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

/*!
 * \file window_map.c
 *
 * \brief GIS Library - Window mapping 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 <grass/gis.h>

#include "G.h"


/*!
 * \brief Adjust east longitude.
 *
 * This routine returns an equivalent <i>east</i> that is
 * larger, but no more than 360 larger than the <i>west</i> 
 * coordinate.

 * <b>Note:</b> This routine should be used only with
 * latitude-longitude coordinates.
 *
 * \param east east coordinate
 * \param west west coordinate
 *
 * \return east coordinate
 */
double G_adjust_east_longitude(double east, double west)
{
    while (east > west + 360.0)
	east -= 360.0;
    while (east <= west)
	east += 360.0;

    return east;
}


/*!
 * \brief Returns east larger than west.
 *
 * If the region projection is <tt>PROJECTION_LL</tt>, then this routine 
 * returns an equivalent <i>east</i> that is larger, but no more than 
 * 360 degrees larger, than the coordinate for the western edge of the 
 * region. Otherwise no adjustment is made and the original
 * <i>east</i> is returned.
 *
 * \param east east coordinate
 * \param window pointer to Cell_head
 *
 * \return east coordinate
 */

double G_adjust_easting(double east, const struct Cell_head *window)
{
    if (window->proj == PROJECTION_LL) {
	east = G_adjust_east_longitude(east, window->west);
	if (east > window->east && east == window->west + 360)
	    east = window->west;
    }

    return east;
}

/*!
 * \brief Initialize window.
 *
 */
void G__init_window(void)
{
    if (G_is_initialized(&G__.window_set))
	return;

    G_get_window(&G__.window);

    G_initialize_done(&G__.window_set);
}