[gdal-dev] Computing my overviews for GeoTIFF

[Even Rouault]

Le 13/07/2021 à 18:24, Javier Jimenez Shaw a écrit :
> Sounds good.
>
> My next question is how to write the overviews data efficiently.
> I see that there is a method "GDALRasterBand * 
> GDALRasterBand::GetOverview ( int i ) ", but for that I need to 
> deinterlace the image (copying it), and call it 4 times. Is there any 
> trick I am missing while calling GDALRasterBand::RasterIO? Maybe some 
> black magic with the pixel and line spaces? The images/overviews I get 
> from the GPU are interlaced (RGBARGBA)
> On the other side there is "GDALDataset::RasterIO(...)", but there is 
> not explicit way to set the overview level.

You can call GetDataset() on the RasterBand returned by GetOverview(). 
Note that this will not necessarily return a non-NULL dataset for all 
drivers, but it will for GeoTIFF.

Internally though this will go through the GDAL block cache (per band), 
so there will be internal deinterlace & reinterlace, at least for 
internal overviews, that by default use pixel-interleaving (for external 
overviews, band interleaving is used)


>
> Thanks
> .___ ._ ..._ .. . ._. .___ .. __ . _. . __..  ... .... ._ .__
> Entre dos pensamientos racionales
> hay infinitos pensamientos irracionales.
>
>
>
> On Tue, 13 Jul 2021 at 14:04, Even Rouault <even.rouault at spatialys.com 
> <mailto:even.rouault at spatialys.com>> wrote:
>
>     Javier,
>
>     You can use the "NONE" resampling method in BuildOverviews() or
>     gdaladdo to create the overviews IFD without allocating any
>     storage, and then you can open the file in update mode to set
>     whatever values you want. APPEND_SUBDATASET=YES will not set the
>     appropriate value for the SubFileType TIFF tag, and thus such
>     pages won't be recognized as overviews
>
>     Even
>
>     Le 13/07/2021 à 13:57, Javier Jimenez Shaw a écrit :
>>     Hi
>>
>>     I am computing the overviews of a GeoTIFF on my own (using the
>>     GPU, much faster), and I want to include them in the tif file
>>     (also in the ovr sidecar file).
>>     What is the best way to do it? Just creating a multipage TIFF (I
>>     guess with the option APPEND_SUBDATASET=YES)? Is there anything
>>     else needed (metadata, tiff tags, etc)?
>>
>>     So far I want to do it in RGBA 8 bit images. (In the future I
>>     want to do it also in float32 images with nodata value and any
>>     number of bands, but no hurry).
>>
>>     I am using GDAL 3.3.1
>>
>>     Any help is welcome.
>>
>>     Thanks.
>>     Javier.
>>     .___ ._ ..._ .. . ._.  .___ .. __ . _. . __..  ... .... ._ .__
>>     Entre dos pensamientos racionales
>>     hay infinitos pensamientos irracionales.
>>
>>
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>
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