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I am using GDAL raster calculator in QGIS. I was getting some funny results where my input raster had "no data" so I ran some tests.

(5<no data) gives 1

(5>no data) gives 0

10 - no data = no data

1/nodata = 2.9e-39

From this I deduce that "no data" values are treated as infinite. Is this correct? I can't find anywhere in the documentation which describes the treatment of "no data" values. This interpretation does not explain why addition or subtraction gives "no data" as the result.

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  • I think it treats is a NaN
    – Ian Turton
    Commented Sep 16, 2021 at 13:39
  • OK, so is NaN treated as infinite?
    – murrayjanemary
    Commented Sep 16, 2021 at 14:31
  • because you aren't supposed to do maths with NaN
    – Ian Turton
    Commented Sep 16, 2021 at 14:46
  • 1
    @IanTurton - that seems completely correct - however, what then 1/nodata or 5<no data does not result in no data as well, but returns a number?
    – Babel
    Commented Sep 16, 2021 at 14:48
  • 1
    There may be some useful information in github.com/OSGeo/gdal/issues/1893.
    – user30184
    Commented Sep 16, 2021 at 15:40

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