rt_raster_pixel_as_polygon()

LWPOLY* rt_raster_pixel_as_polygon	(	rt_raster	rast,
		int	x,
		int	y
	)

Get a raster pixel as a polygon.

The pixel shape is a 4 vertices (5 to be closed) single ring polygon bearing the raster's rotation and using projection coordinates

Parameters

raster	: the raster to get pixel from
x	: the column number
y	: the row number

Returns

the pixel polygon, or NULL on error.

Definition at line 610 of file rt_geometry.c.

References lwpoly_construct(), ptarray_construct(), ptarray_set_point4d(), rt_raster_get_srid(), rt_raster_get_x_offset(), rt_raster_get_x_scale(), rt_raster_get_x_skew(), rt_raster_get_y_offset(), rt_raster_get_y_scale(), rt_raster_get_y_skew(), rtalloc(), POINT4D::x, and POINT4D::y.

Referenced by RASTER_getPixelPolygons(), RASTER_nearestValue(), and test_raster_pixel_as_polygon().

{
    double scale_x, scale_y;
    double skew_x, skew_y;
    double ul_x, ul_y;
    int srid;
    POINTARRAY **points;
    POINT4D p, p0;
    LWPOLY *poly;

                assert(rast != NULL);

    scale_x = rt_raster_get_x_scale(rast);
    scale_y = rt_raster_get_y_scale(rast);
    skew_x = rt_raster_get_x_skew(rast);
    skew_y = rt_raster_get_y_skew(rast);
    ul_x = rt_raster_get_x_offset(rast);
    ul_y = rt_raster_get_y_offset(rast);
    srid = rt_raster_get_srid(rast);

    points = rtalloc(sizeof(POINTARRAY *)*1);
    points[0] = ptarray_construct(0, 0, 5);

    p0.x = scale_x * x + skew_x * y + ul_x;
    p0.y = scale_y * y + skew_y * x + ul_y;
    ptarray_set_point4d(points[0], 0, &p0);

    p.x = p0.x + scale_x;
    p.y = p0.y + skew_y;
    ptarray_set_point4d(points[0], 1, &p);

    p.x = p0.x + scale_x + skew_x;
    p.y = p0.y + scale_y + skew_y;
    ptarray_set_point4d(points[0], 2, &p);

    p.x = p0.x + skew_x;
    p.y = p0.y + scale_y;
    ptarray_set_point4d(points[0], 3, &p);

    /* close it */
    ptarray_set_point4d(points[0], 4, &p0);

    poly = lwpoly_construct(srid, NULL, 1, points);

    return poly;
}

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