GDAL's AAIGRID driver appears okay after all.GDAL's GeoTIFF driver will likely be patched specifically for Leveller. It has a spec violation but GDAL's maintainer isn't interested in resolving it (sigh). If anyone sets a RasterPixelIsPoint geokey, the projection origin will be shifted to conform to GDAL's pixels-as-areas when reading.
DTED: still being looked at. Ray