When I configure the Nodata Value argument in the Build Virtual Raster tool (QGIS 3.4.7) equal to -9999 I have obtained an unexpected result, as shown in the figure below: enter image description here

On the other hand, if I adopt Nodata Value = 0 the result is better, but without the representation of pixels with values = 0:

enter image description here

Raster layer cuts were done with the GDAL Clip Raster by Mask Layer tool (Nodata value = -9999, Match the extent of the mask layer, Profile: default, Output data type: Float64).

Is this a bug in the QGIS 3.4.7 Build Virtual Raster tool?

  • Probably means your rasters do not have a -9999 value. – user2856 May 11 at 0:10
  • Sorry, it does. Because: i) GDAL Clip Raster by Mask Layer tool was configured with Nodata value = -9999 when the images were cut; ii) in Layer Property> Information I checked that all 4 bands have No-Data = -9999; iii) the Merge tool (configured with Output Data Type = Float64; Input Pixel Value to Treat the Nodata = -9999; Assigned Specified Nodata Value to Output = - 9999) works fine and creates the output file correctly. – Sergio May 11 at 12:00
  • You may have specified -9999 as the nodata value, but that doesn't mean your data actually contains any -9999 values. If you specify 0 as nodata in the Build Virtual Raster tool and the mosaic appears as it should then those pixels actually do have 0 not -9999 and your issue is occurring before you use the Build Virtual Raster tool. – user2856 May 12 at 2:13

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