[qgis tutorial] transparency in gdalbuildvrt command

[landryb]

It's somewhat easy to handle transparency, but that depends on the remote data you're looking at. In your case, adding -srcnodata 0 to the gdalbuildvrt command tells gdal to consider pixels with 0 value (ie real black) as transparent, which gives the following here: https://i.imgur.com/Feca8ny.png.

The BG is red in my QGIS precisely for this, to see if data is transparent..

Of course, this has some drawbacks,cf https://i.imgur.com/4EamrFS.png:

• if there are real black pixels 'inside' the image, they're now transparent too
• it also shows the compression artifacts on the edges

Sadly, those shortcomings can only be fixed "at the source"..

[landryb]

The other option is to create an intermediate VRT manually clipping the area where you know you have no data... but as long as your source image doesnt ship with an alpha channel or a NODATA value in its bands, it's hard to workaround this..

[cholmes]

Sorry for the super long response on this, my github filters sometimes just lose the notifications. But thanks so much! Just added it in. It does seem to not be the best solution, with the transparent pixels inside the image.

Hopefully we can figure out better handling of nodata values, perhaps using SpatioTemporal Asset Catalogs in conjunction with COG's. cc @mojodna as I think he was just telling me about this problem.