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I need to get information about any occurrences of NoData in an elevation raster. Simply by looking at the raster it is not possible to determine if and where any holes of NoData are present, so a technical method is needed.

Primarily I would like to obtain polygons of any NoData areas in the raster (i.e. vectorization). Another option would be to obtain a 1-bit raster which simply indicates true/false for NoData, but vector features would be much better.

How can this be accomplished?

This Question is more or less unrelated to a specific software, though I prefer using free software like QGIS, GDAL/OGR etc.

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First, you need to isolate NoData pixels from other values. With this raster, you can obtain polygons.


An example raster with random values: NoData (white spaces), 1 (purple), 2 (green) and 3(yellow).

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Use raster calculator to divide by the same raster to obtain a new raster with values 1 and NoData:

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Result:

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Use GRASS command r.null to fill NoData values with a value. I used 2 for this purpose:

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Use Raster / Conversion / Polygonize to convert to vector and select by the previously set value:

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Save as with selected features:

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