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Is it possible to output a PNG in a base64 string so that can be directly loaded into a browser? I've read through the PostGIS documentation which refer to the GDAL output formats. The GDAL output formats here state the following:

GDAL includes support for reading, and creating .png files. Greyscale, pseudo-colored, Paletted, RGB and RGBA PNG files are supported as well as precisions of eight and sixteen bits per sample.

Regarding MapServer, the only reference I can find is an unanswered question asked on the mailing list six years ago.

I am wondering if I can generate a png text string in the following form so that it can be loaded into a browser using the Data URI scheme: 

<img alt="" src="data:image/x-png;base64,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" />

I would like to test this approach, as I am interested in the approach that MySociety used when creating Mapumental. In the description of how they made this tool, they refer to color-cycling of a base64 PNG string. The approach used by Mapumental is very complex - I am just interested in exploring how to even start this approach.

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Couldn't you try something like...

SELECT encode(ST_AsPNG(rast), 'base64') FROM foo

Granted, I have no idea if that'll work but it is worth a shot.

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  • Yes! That worked. I used SELECT encode(ST_AsPNG(ST_AsRaster(ST_Buffer(ST_Point(1,5),10),150, 150, '2BUI')), 'base64') and was able to load that into my browser.
    – djq
    Commented Nov 21, 2012 at 5:06

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