Hi Gerd,
What makes you think that 0,0 is used instead of the upper left cornen given in the DEM section header(s)?
In Garmin's DEM coordinates are always a multiple of DEM pixel size (dem-dists). The result is, that all DEMs data are aligned with 0;0. It makes easy to join different tiles, since all tiles share the same alignment. Garmin uses DEM pixel size, which is not optimal for HGT. Looks like they don't care about HGT alignment, while obviously they use SRTM data. There should be no shifting of DEM, if DEM coordinates are strictly respected by Mapsource od BaseCamp. But there could be artifacts on tile borders. Anyway, it is just a guess. We can make some test with Mapsource, but would be difficult to test all different devices. That is why I would prefer to make DEM exactly like Garmin, which means, that we can't get good alignment with HGT. -- Best regards, Andrzej