So on importing a heightmap, from differing sources of high-res satellite imagery( 3DEP 1M, and 1/3 arc Second, or 2M ArcticDEM)
I am seeing a grid in the landscape which has a slightly raised profile once imported into Unreal.
The images are being processed in QGIS prior to import as the GeoTiff format needs to be converted and the size reduced, so maybe something there could be the issue, but I have been doing this over a couple of years now and never seen this before. I wonder if it has started since going over to 5.2 and I have simply not noticed it immediately.
But has anybody had this problem and know if it is due to an artifact in the source imagery or processing in QGIS or is produced on importing the heightmap into Unreal, and either way, how have you overcome this?
Note: I first noticed this when upscaling in Unreal, but I have tried on 100 and it is the same.
I’ve worked it out myself, it turns out this is an in fact an artifact side effect of using the GDAL functions in QGIS, namely I was resizing in there, rather than in Gimp as I did previously. Gimp LoHalo is the cost free way!
Define resizing.
If you have to stretch a 20m DTM into a 1m dtm. You have to radial blur at 20px and “live” withe the loss of accuracy.
If all you are doing is creating tile sets at the proper size (you either have a 1m dtm, or are using whatever it is in native scale) you may want to consider exporting natively into png16 at whatever size the original tiles were (which are never too big to cause issues), and then re-process them with Nip2 to cut up into level-appropriate tiles.
I think I did define resizing, a reduction in image size. But if you want more I think, merged DEMs were output in GeoTiff at 50000px sq (if memory serves) and I needed to resample with final size of 16321. I have not been able to output png16 directly from QGIS, so I have used GIMP to convert the GeoTIFFs.
Realistically the grid effect could be due to lighting, since the way the engine handles it has changed somewhat drastically.
But, if it is a direct result of the resizing process, then a simple radial blur applied universally will sort out the artifact.
It would be simiar to using the landscape smooth tool at a very low settings.
Your peaks will also flatten somewhat.
Note that while I’m not aware of a program which does it, a coded script analizing the graded levels would produce better results.
Basically if the value between 2 pixels is above a certain treshold, you soften the area around it to get the values within an acceptable range.
Conceptually, you could do this by pulling a slope map and using the map as a filter to fix problem spots…
