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I have a raster layer and a polygon layer. The raster layer has values between 0 and 600. I want to calculate the average of all values above 0 within each polygon.

The only solution I came up with so far is to clip the part of the polygons that overlaps with a non-zero (positive) raster value, and then calculate the zonal statistic only for the clipped part. Since the data is quite large, this method is not practical.

Is there a faster way, e.g. set the grid values = 0 to NODATA (if this is possible) and then calculate the average value? Unfortunately I have little experience with raster data.

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Convert raster pixels with value 0 to nodata cells using Raster Calculator. Divide the raster's value by itself: a division by 0 will return nodata.

For all other pixels, to keep the value as it is, divide the pixel value by itself and multiply it again by itself.

  • 5 / 5 * 5 -> 5
  • 0 / 0 * 0 -> NODATA

Use this expression in raster calculator, where raster is the name of your raster layer:

"raster@1" / "raster@1" * "raster@1"

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