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Does anybody know why building pyramids in QGIS using the "build pyramids" button from the properties menu (tab: pyramids) is a lot faster than command line gdaladdo or Raster->Misc->Build Overviews?

To rule out some questions that may arise:

  • I didn't build less pyramids with the properties dialogue
  • I didn't choose different methods
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My guess - and this is only a guess :)

When you use the QGIS pyramid building function, it directly calls the GDAL method GDAL_BuildOverView on a raster which has already been cached in memory, in whole (or in part).

Whereas, if you go via the command line, the raster will be need to be loaded in again from scratch.

The same goes for running Raster > Misc > Build overviews, which is a wizard which calls gdaladdo with the same settings.

I’d love to know if this is the actual cause, or if it’s a difference with the pyramid settings which means that interpolation is needed.

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