[gdal-dev] GDAL Maintainers Meeting Minutes

[Even Rouault]

Javier,
>
>       * use TILED=YES by default in GTiff driver
>
> Was that decided? As some people pointed (including me) a big tiled 
> geotiff without overviews take ages to load in QGIS.

No, pretty much all items are still just ideas (well, perhaps besides 
enabling Python exceptions by default, which I can't really imagine 
postponing any further than a 4.0 :-)), some of them not necessarily 
desirable or turning out to not be easily implementable. Most of them 
will only make sense if we have sufficient community buy-in, as they'll 
break things for existing users.

Your concern about big tiled geotiff without overviews is a real one. 
One idea I just got to avoid that that just came to mind (possibly not a 
good one as I'm detailing it, but anyway here's my brain dump :-)) could 
be that on creation of a tiled GeoTIFF larger than let's say 10k x 10k 
pixels, GDAL would automatically create a nearest-neighbour overview of 
let's say at most 512 pixels in width and height and update it whenever 
a tile is updated,. So the overview would likely have to be uncompressed 
(not entirely clear if all GeoTIFF capable software around is able to 
deal with different compression methods for overviews versus full 
resolution image), so its size remains constant when tiles are updated. 
And it would have to be discarded when explicit ones are created. And 
the logic of selection of overviews would also have to be modified to 
select that overview in a more aggressive way than the current logic 
does (cf 
https://gdal.org/api/gdaldataset_cpp.html#_CPPv4N11GDALDataset8RasterIOE10GDALRWFlagiiiiPvii12GDALDataTypeiPi8GSpacing8GSpacing8GSpacingP20GDALRasterIOExtraArg). 
Perhaps an open option that a viewer such as QGIS could set? So quite a 
bunch of extra complications in the GeoTIFF driver which is already 
super complicated.

Even

-- 
http://www.spatialys.com
My software is free, but my time generally not.
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