On lundi 11 septembre 2017 15:43:47 CEST Andreas Neumann wrote: > Hi, > > I received a DTM from a Swiss province (OpenData) which is of the > following format: > > One coordinate per line, already gridded. See f.e. > > 2708001.00 1218001.00 1541.52 > 2708003.00 1218001.00 1542.35 > 2708005.00 1218001.00 1542.98 > 2708007.00 1218001.00 1543.58 > 2708009.00 1218001.00 1544.20 > 2708011.00 1218001.00 1545.13 > 2708013.00 1218001.00 1545.88 > > The issue is that further down the file there seems to be an issue of > ordering the coordinates. gdalinfo produces the following error: > > ERROR 1: Ungridded dataset: At line 4125001, change of Y direction > gdalinfo failed - unable to open 'DTM_swissALTI3D_XYZ.txt'.
Andreas, the message is probably misleading. It means that from the XYZ point of view, it cannot handle the dataset since it doesn't match its expectations: ie successive lines with same Y and constant positive X step, and when changing lines, with a constant positive or negative Y step. The driver says probably a bit quickly that the dataset is ungridded. > > If GDAL could open the data - it would open as ungridded data - right? > Issue is, this data is already gridded as you can see above. I actually > want to save this is a gridded GeoTIFF file for later usage in QGIS. > > Is there still a chance that GDAL can open this data set, even if > coordinates are out of order? Not by the XYZ driver in its current design where it tries to not ingest the full file into memory. It does a preliminary scan to check that the file organization meets its criteria, but then reads its progressively efficiently. One could perhaps have a more relaxed mode that would require more memory and/or be less I/O efficient for datasets such as the one you tried. You might try to open this file with the CSV driver and use gdal_grid (with a search radius of 2 since this apparently the horizontal resolution) to produce a GeoTIFF. You might possibly do a preliminary conversions of the CSV to shapefile with spatial index or GPKG to improve performance of gdal_grid. Even -- Spatialys - Geospatial professional services http://www.spatialys.com
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