Why does gdal2tiles sometimes produce a tileset where the image does not fill the tiles?

Question

I'm using gdal2tiles on a vrt that I've warped from Mercator to QSC. I'm using the 'raster' profile. The resulting tiles look correct but there transparent strips on the upper and right edges of the right-most and top-most tiles:

The above image shows tiles 1,1,0 and 1,1,1

My call to gdal2tiles looks like this:

gdal2tiles.py --profile=raster -z 0-4 face.tif outFilePath

Answer 1

This is because gdal2tiles makes tiles of 256x256 pixels. If your original picture isn't a multiple of 256 is width and height, you end up with some empty space on the top and right.