[gdal-dev] mosaicking files with partial overlap and binary mask

[Patrick Young]

Hi Daniele,

Even added this functionality to VRTs just recently, see

https://lists.osgeo.org/pipermail/gdal-dev/2020-December/053178.html

I think it is slated for GDAL 3.3 but you could always build the bleeding
edge.

Patrick

On Wed, Jan 27, 2021 at 3:50 AM Daniele Romagnoli <
daniele.romagnoli at geo-solutions.it> wrote:

> Hi list,
> I have some TIFF datasets with partially overlapping edges and embedded
> binary masks to keep into account which parts along the edges should be
> masked out.
> When showing all the images on QGIS it looks good since the binary mask do
> its job by making the "black/white" overlapping edge masked out.
>
> Now I need to create a single TIF from all of these images.
> I have tried with gdalbuildvrt but it doesn't produce good result.
> Checking the doc I saw this:
>
>
> *If there is some amount of spatial overlapping between files [...]
> currently, alpha channel is not taken into account to do alpha compositing
> (so a source with alpha=0 appearing on top of another source will override
> is content). This might be changed in later versions.  *
>
> So I think it's expected and I have switched to gdal_merge.py.
> It works better since it does alpha compositing but it looks like the
> result doesn't preserve the binary mask which I still need since I have M
> groups of N files which I need to process in 2 passes:
> - the inner group of N files get merged using the binary mask to a bigger
> file.
> - all the M bigger files get mosaicked again to a single huge file.
>
> I will spend some more time in testing different attempts.
> In the meantime, do you have any suggestion or past experience on how to
> deal with that?
> Side note: I have vague memory of gdal_merge being somehow memory bounded,
> throwing memory allocation errors when trying to compose big images. This
> is why in the past I was using gdalbuildvrt to do composition (without
> overlapping).
>
> Thanks in advance.
> Regards,
> Daniele
>
>
>
>
> --
> Regards,
> Daniele Romagnoli
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