[gdal-dev] problem rasterizing categorical data from shapefile - 0 values at some intersections

[Chaitanya kumar CH]

Etienne,

Rasters of type Byte cannot hold values below 0. So, the nodata value of -1
is not practical. It's better to choose 0 or 255 depending on your data or
choose a different data type.

Your problem arises because the two geometries in the shapefile overlap in
some places and leave some gaps between them in other places.
Consider selecting only one feature using the -where option in
gdal_rasterize. You can also use the -at option but it may not work at all
resolutions.

On Fri, Aug 5, 2011 at 7:40 AM, Etienne <etiennesky at yahoo.com> wrote:

> Hi all,
>
> I am trying to create a raster file with categorical data (land
> vegetation/cover positive indices) from a shapefile containing 1 layer of
> polygons.
>
> I use the following command:
> gdal_rasterize  -tr 0.0005 0.0005  -a_nodata -1 -of GTiff  -a_srs EPSG:4618
> -a "CLASSE_ID" -ot Byte -init -1 -l region1 region1.shp region1-3.tif
>
> This creates a  map which looks good, but there are some holes in the data,
> (individual pixels with a value of 0) at the intersection of 2 polygons. It
> looks like the
> intersections pass through the exact center of these pixels. These pixels
> are not set to missing(-1). Depending on the output resolution, different
> pixels get set to a value of 0.
>
> Has anyone ran into this problem?  Any idea how to fix this?
> Those interested will find 2 small shapefiles here: http://db.tt/3X4hI45and
> http://db.tt/phqnGci
>
>
> I tried using gdal_grid, but it doesn't seem to support a shapefile with
> POLYGONs.
>
> many thanks!
> Etienne
>
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>



-- 
Best regards,
Chaitanya kumar CH.

+91-9494447584
17.2416N 80.1426E
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