[gdal-dev] Can overviews be fiddled?

[Jukka Rahkonen]

Hi,

My colleague wants to know if it is possible to build a bigtiff image that gets
overviews from different datasets. The aim is to have a one scale dependent
rastes map image. Idea is quite attractive but is is possible to do?

The procedure might start from a bunch of external .ovr files

bigtiff_1 -> gdaladdo -ro 2 4    #for near zoom
bigtiff_2 -> gdaladdo -ro 8 16   #for far zoom
bigtiff_3 -> gdaladdo -ro 32 64  #for more far zoom 

If overviews bigtiff_1.ovr, bigtiff_2.ovr and bigtiff_3.ovr could be combined
and renamed as bigtiff_1.ovr we the result would be a bigtiff_1 image which
would look like bigtiff_2 and bigtiff_3 when zoomed out.

I can see problems if working with real world maps because the originals would
have different pixel sizes but is it possible even in theory to construct hand
made overviews?  It could be a pleasure to use a single image as a background
map in GDAL based GIS programs instead of playing with several scale dependent
layers.

-Jukka Rahkonen-