Re: [gdal-dev] create classified PNG from ASCIIGrid

[Stephen Crawford]

OK, looks like [3] for me.  Thanks.

On 7/28/2011 3:01 PM, Chaitanya kumar CH wrote:

The closest thing you can do without doing any coding is to use the gdal_contour utility[1] to create a vector file and then use gdal_rasterize [2] to burn them back to a raster. If you use appropriate options, all your pixels will be clamped to the discrete levels used in gdal_contour. It's straight forward to apply a color table to that.

If you want to do this using a script, refer to the gdal API tutorial[3]. You'll have to do the classification while you read and write the pixels using GDALRasterIO(). You can set the color table too.

Note that there may be some differences along the edges of classified pixels between these two methods. The lines generated by gdal_contour may go through the area of a pixel and could change the burn value.

[1]: http://www.gdal.org/gdal_contour.html
[2]: http://www.gdal.org/gdal_rasterize.html
[3]: http://www.gdal.org/gdal_tutorial.html

On Fri, Jul 29, 2011 at 12:05 AM, Stephen Crawford <src...@psu.edu <mailto:src...@psu.edu>> wrote:

    Thanks for the reply.  I had looked at these before, and then
    looked again after your note, but I just don't understand how I
    map the climate variable values to different colors in the
    palette, along the lines of:

    tmax < 30            |  color1
    30 < tmax < 50   | color2
    tmax > 50            | color3

    Thanks,
    Steve


    On 7/27/2011 1:01 AM, Chaitanya kumar CH wrote:

    Sorry, here are the links.

    [1]: http://www.gdal.org/rgb2pct.html

    [2]: http://www.gdal.org/gdal_vrttut.html
    [3]: http://www.gdal.org/formats_list.html

    On Wed, Jul 27, 2011 at 10:30 AM, Chaitanya kumar CH
    <chaitanya.ch <http://chaitanya.ch>@gmail.com <http://gmail.com>>
    wrote:

        Stephen,

        The docs for rgb2pct.py script [1] has an example that shows
        how to convert to a paletted image using hand made VRT file.
        You can use the "-of PNG" option to set the destination
        format as png and the -pct option with your VRT file.


        On Wed, Jul 27, 2011 at 2:42 AM, Stephen Crawford
        <src...@psu.edu <mailto:src...@psu.edu>> wrote:

            Hi All,

            I have 60 or so asciiGrids of climate data that I would
            like to tun into PNGs, with the climate values classified
            by color.  I would like to script this process using
            Python.  Is there a way to do this with GDAL?  Or if not,
            is there any other open source way to do this?

            Thanks,
            Steve


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-- Best regards,

        Chaitanya kumar CH.

        +91-9494447584
        17.2416N 80.1426E

-- Best regards,

    Chaitanya kumar CH.

    +91-9494447584
    17.2416N 80.1426E

-- Stephen Crawford

    Center for Environmental Informatics
    The Pennsylvania State University
    src...@psu.edu  <mailto:src...@psu.edu>
    814.865.9905




--
Best regards,
Chaitanya kumar CH.

+91-9494447584
17.2416N 80.1426E

--
Stephen Crawford
Center for Environmental Informatics
The Pennsylvania State University
src...@psu.edu
814.865.9905


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