Hi Mark,
Can you elaborate on what you mean by "resultant raster does not map to
the reference raster"?
The output from ST_AsRaster should result in a raster with the same
SRID, scale and skew as the reference raster. The output raster should
also be aligned with the reference raster as tested by ST_SameAlignment.
-bborie
On 06/23/2012 11:04 PM, Mark Wynter wrote:
> I can rasterise a vector layer, but I'm having trouble mapping it to a
> reference raster.
>
> The reference raster, called dummy_rast is a 1x1 raster tile with a height
> and width of 500pixels, each of 250m in size. I created using a pl/pgsql
> function:
> SELECT make_tiled_raster('public', 'dummy_rast', 576000, -3780000, 1, 1, 500,
> 500, 250, -250);
> The result is
>
> srid | scale_x | scale_y | blocksize_x | blocksize_y | num_bands |
> pixel_types | nodata_values
> ------+---------+---------+-------------+-------------+-----------+-------------+---------------
> 3577 | 250 | -250 | 500 | 500 | 1 | {8BUI}
> | {NULL}
>
>
> I now wish to burn a vector layer onto this raster:
>
> CREATE TABLE viewshed_rast AS
> WITH vt as (SELECT ST_Union(geometry) as geometry FROM viewshed_vectors)
> SELECT rt.rid, ST_AsRaster(vt.geometry, rt.rast, '8BUI', 120, 100) as rast
> FROM dummy_rast as rt, vt;
>
> The result is
> srid | scale_x | scale_y | blocksize_x | blocksize_y | num_bands |
> pixel_types | nodata_values
> ------+---------+---------+-------------+-------------+-----------+-------------+---------------
> 3577 | 250 | -250 | 67 | 38 | 1 | {8BUI}
> | {100}
> (1 row)
>
> I do not understand why the resultant raster does not map to the reference
> raster? Refer screenshot attached showing the resultant layers in QGIS.
> The upperleftx and upperlefty, and the block size of the resultant raster are
> defined by the extent of the vector layer and not the reference raster.
>
> Is there something obvious I'm doing wrong? Thanks.
>
>
>
>
>
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--
Bborie Park
Programmer
Center for Vectorborne Diseases
UC Davis
530-752-8380
[email protected]
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