I'm trying to create hillshades from Czech elevation data (Fundamental Base of Geographic Data of the Czech Republic (ZABAGED®) - altimetry - grid 10x10 m) - a demo files is available here: http://geoportal.cuzk.cz/UKAZKOVA_DATA/GRID10x10.zip
I combine some of their txt files using some bash scripts and then create a GeoTiff using gdal_grid. The resulting GeoTiff looks like this when imported in QGIS:
As a next step I'd like to create hillshades using the Raster->Analysis->DEM and the result looks like this:
I made sure to use the bilinear option when rewarping the raster and already tried basically all available algorithms of gdal_grid.
Not sure if this is relevant, but that's how the hill shade TIFF looks like when opend in OS X Preview:
What's the source of these artifacts and how to avoid them?