Function msMapComputeGeotransform

mapobject.c:386–433

extern int InvGeoTransform( double *gt_in, double *gt_out );

int msMapComputeGeotransform( mapObj * map )

{
    double rot_angle;
    double geo_width, geo_height, center_x, center_y;

    map->saved_extent = map->extent;

    /* Do we have all required parameters? */
    if( map->extent.minx == map->extent.maxx 
        || map->width == 0 || map->height == 0 )
        return MS_FAILURE;

    rot_angle = map->gt.rotation_angle * MS_PI / 180.0;

    geo_width = map->extent.maxx - map->extent.minx;
    geo_height = map->extent.maxy - map->extent.miny;

    center_x = map->extent.minx + geo_width*0.5;
    center_y = map->extent.miny + geo_height*0.5;

    /*
    ** Per bug 1916 we have to adjust for the fact that map extents
    ** are based on the center of the edge pixels, not the outer
    ** edges as is expected in a geotransform.
    */
    map->gt.geotransform[1] = 
        cos(rot_angle) * geo_width / (map->width-1);
    map->gt.geotransform[2] = 
        sin(rot_angle) * geo_height / (map->height-1);
    map->gt.geotransform[0] = center_x 
        - (map->width * 0.5) * map->gt.geotransform[1]
        - (map->height * 0.5) * map->gt.geotransform[2];

    map->gt.geotransform[4] = 
        sin(rot_angle) * geo_width / (map->width-1);
    map->gt.geotransform[5] = 
        - cos(rot_angle) * geo_height / (map->height-1);
    map->gt.geotransform[3] = center_y 
        - (map->width * 0.5) * map->gt.geotransform[4]
        - (map->height * 0.5) * map->gt.geotransform[5];

    if( InvGeoTransform( map->gt.geotransform, 
                         map->gt.invgeotransform ) )
        return MS_SUCCESS;
    else
        return MS_FAILURE;
}

/************************************************************************/
/*                         msMapPixelToGeoref()                         */