Elevation scaling best practices?

[david.norlin]

We are encountering a scaling issue after generation of our terrain.  It seems as though each pixel/polygon is exponentially higher than it should be (this is at 1m/px resolution, georeferenced).  This seems like a very easy fix - just adjust scale, but I am having a hard time figuring out what the actual height of the terrain is in-engine, so scaling it is guesswork.  This is real-world terrain, so accuracy is crucial.  

What is the best way to to properly scale a terrain?  Is the max value displayed in Unigine somewhere? 

Also, in the second pic, what causes this unusual plateau-like feature?  Is there a terrain bounding box in effect?  

[morbid]

Hi David,

not sure that there are best practices for scaling of georeferenced height-map :)

Each geo-referenced raster has its own scale value that is supposed to be correct. However, you can add scale multiplier in landscape tool. The formula is simple: each pixel of elevation file is multiplied by landscape tool scale and gdal scale.

I think it worth to check the scale value of the original file. Is it correct? In QGis you can use QGIS2threejs plugin to visualize elevation in 3D. The same option is available in GlobalMapper.

Plateau also looks for me as a source file issue.

I could've said more if I had a sample of this source. Can you send one?

Thank you!

 

[david.norlin]

Hi Morbid,

Thanks for the advice.  I think I tracked the issue down to a unit conversion problem in the export from World Creator, specifically with how it is imported back into QGIS.  It was taking the height in feet specified in World Creator and converting it to meters, so the max elevation was actually 255 meters instead of only 72.  Mystery solved, and I found that the correct scale value should be .304.  It was easy to see when I used gdalinfo on the file. 

Now, the terrain shape looks perfect, but it did not get rid of the strange terrace-like surface.  

This is strange, because in World Creator, the island looks very natural and smooth.  Is there a better way to prepare an edited DEM for import?  Steeper slopes do not have this problem and they look more natural - only in smoother, open areas (which is most of the island...lol).   I wonder if this is because I'm exporting at too high of a resolution?  Resolution is 50x50k px, at 1m resolution.  My first experiment with trying to improve DEMs...

I have sent you the file via PM.

Thanks!

Edited October 9, 2018 by david.norlin

[david.norlin]

Morbid,

I have made some progress tonight and managed to get rid of the terrace-like surface.  I did this by building the file entirely through the raw World Creator export and then georeferencing using gdal command line, never bringing it into QGIS.  I found that QGIS was reducing the file to 8 bit (instead of 16 or 32) and removing lots of data. Now, the actual terrain surface is very good, but elevation scaling is once again a problem.  The first time I brought it in to Unigine, it was scaled so enormously that it was reaching the stratosphere.  I had to use an elevation scale of .005 - as low as I could go - to get it even remotely reasonable.  It is still too tall, but it is much better than before.  I have sent you the new file via PM.