I am struggling with this several days and now its time to ask how to do it in QGIS.
I have very detailed 27 ASC grid files with overall size of 9 GB created from 1m contours of large area (600 m2). The goal is to merge all this data into one DEM for easier handling (output will be smaller i think ?) and later to create a slope, hillshade color shaded reliefs ,etc for whole area easier.
- I have simplified contours for whole area in SQL Sever which are much less in size than original ones.
- ASC files are created from original contour data and I would like to create one DEM from that.
I have tried next QGIS/GRASS solutions with simplified contours of a whole area:
but I had only success in rasterizing contours (v.to.rast.attr). That creates a 218 MB TIF with dimensions of 37945 x 30143. But, in the next step when I start 'r.surf.contour' it just hangs forever (last try was 24 hour long and then I quit, although process was very active and consumed almost all memory (6GB RAM). Is this too large dataset and this is normal execution time on modern PC configuration ?
Other way would be to use ASC files and to merge it to one DEM. If someone could give me information how to do it efficently or some detailed workflow would be great.
I would say that the purpose of DEM will be to create a shaded relief as a background for printing 1:5000 maps.
Well I have converted all 27 ASC to GeoTiff and also realized there are 3 more grids (.grd) which has been made by GS Surfer 12. I converted them also in GeoTiff. Now when I try to build VRT next thing happens:
The first of 27 GeoTifs are joined into VRT but I've lost all elevations. VRT have only one value (167, which is the lowest value from all dem's included).
Those 3 files built from Surfer GRD have somehow different characteristics and it wont join with others.
> Warning 6: gdalbuildvrt does not support heterogenous band > characteristics. Skipping D:/DEM (GeoTIFF)/OF_IZO_28_dem.tif
gdalinfo for one tif in original group:
Driver: GTiff/GeoTIFF Files: D:/DEM (GeoTIFF)/OF_IZO_27_dem.tif D:/DEM (GeoTIFF)/OF_IZO_27_dem.tif.aux.xml Size is 5001, 5001 Coordinate System is `' Origin = (7584999.500000000000000,4795000.500000000000000) Pixel Size = (1.000000000000000,-1.000000000000000) Image Structure Metadata: COMPRESSION=PACKBITS INTERLEAVE=BAND Corner Coordinates: Upper Left ( 7584999.500, 4795000.500) Lower Left ( 7584999.500, 4789999.500) Upper Right ( 7590000.500, 4795000.500) Lower Right ( 7590000.500, 4789999.500) Center ( 7587500.000, 4792500.000) Band 1 Block=5001x1 Type=Float32, ColorInterp=Gray Min=243.000 Max=834.072 Minimum=243.000, Maximum=834.072, Mean=503.092, StdDev=130.621 NoData Value=-1 Metadata: STATISTICS_MAXIMUM=834.07208251953 STATISTICS_MEAN=503.0916431759 STATISTICS_MINIMUM=243 STATISTICS_STDDEV=130.62100147903
gdalinfo for one tif made from Surfer .grd>
Driver: GTiff/GeoTIFF Files: D:\DEM (GeoTIFF)\OF_IZO_31_dem.tif D:\DEM (GeoTIFF)\OF_IZO_31_dem.tif.aux.xml Size is 2125, 3512 Coordinate System is `' Origin = (7587875.569015772100000,4790000.499983053700000) Pixel Size = (0.999968455743971,-0.999966106522373) Image Structure Metadata: COMPRESSION=PACKBITS INTERLEAVE=BAND Corner Coordinates: Upper Left ( 7587875.569, 4790000.500) Lower Left ( 7587875.569, 4786488.619) Upper Right ( 7590000.502, 4790000.500) Lower Right ( 7590000.502, 4786488.619) Center ( 7588938.036, 4788244.560) Band 1 Block=2125x1 Type=Float64, ColorInterp=Gray Min=409.000 Max=1239.595 Minimum=409.000, Maximum=1239.595, Mean=679.431, StdDev=154.121 NoData Value=1.7014100000000001e+038 Metadata: STATISTICS_MAXIMUM=1239.5948358501 STATISTICS_MEAN=679.43099985765 STATISTICS_MINIMUM=408.9999998738 STATISTICS_STDDEV=154.12086745843
How I would correct this and get all grids in VRT with preserved elevations ?