[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 <src176 at psu.edu 
> <mailto:src176 at 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
>>         <src176 at psu.edu <mailto:src176 at 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
>>
>>
>>             _______________________________________________
>>             gdal-dev mailing list
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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
>     src176 at psu.edu  <mailto:src176 at 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
src176 at psu.edu
814.865.9905

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