If you initialize empty overviews ( BuildOverviews("NONE", ... ) ), then
you can read the downscaled version of the original geotiff and put that
in the target overviews. Of course you'll pay the price of
decompression/recompression. By using directly the libtiff API, you
could save that
Even
Le 30/07/2021 à 20:19, Javier Jimenez Shaw a écrit :
Hi
I want to make a (power-of-two) downscaled version of a geotiff with
overviews efficiently with C++ (not from the console).
Let's say I have a geotiff with overviews (external or internal), and
I want a copy of it, but at 50% of the size. That is just removing the
"base" of the pyramid, but keeping all the other levels. Then voilà,
there you have the geotiff 50% smaller, with the overviews already
there, almost without any computation. The same for 25% (and any power
of 2).
However I do not figure out how to do it efficiently in C++. If I
understand correctly, CreateCopy is producing an image with the same
size. So to downscale I have to create a new image, read downscaled
(that will use the overviews) and write. But later, I have to recreate
the overviews on the new image... that are already in the original image.
Is there any way to make it efficiently? (as we have the data there)
Thanks.
.___ ._ ..._ .. . ._. .___ .. __ . _. . __.. ... .... ._ .__
Entre dos pensamientos racionales
hay infinitos pensamientos irracionales.
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