Large (60x90 degrees) DEM tile import - stretching

[mt_sabao]

Hi all,
I'm trying to import big DEM tiles (60x90 degrees: Add Terrain> Heightfield (Load DEM)> *.IMG ), geo-referenced on Terragen3. They seem to be going to the correct position on the planet, but the tiles far away from the apex seem to be getting stretched. Am I doing something wrong or is there no way around this: geo-referenced images far from the apex will always be stretched? 
Thanks in advance
Luis

[cyphyr]

If your project will allow it you can always set the lat/long apex in the planet tab to the centre coordinates of your DEM. This will move the dem to the "north pole" where distortions are at a minimum.
I suspect you will still get some distortion at the edges however.
Don't forget to remove uncheck the "flatten surface first" box in the dem loader.
Richard

[mt_sabao]

Thanks for your reply. However,  I have DEM tiles covering the entire planet, so they can not be moved. So this means, that any tile away from the apex will always be stretched, no way around it? Doesn't make much sense. What's the purpose of have them geo-referenced then, if the ones far from the apex will get distorted? 

[Oshyan]

This is most likely happening because the heightfield is displacing along the Y axis, and Y is not always going to be perpendicular to the planet's surface. We're looking at adding an option to displace along the normal, which should address this issue.

- Oshyan

[mt_sabao]

Thanks for your reply. This is too bad then, I cannot go through with my project i guess then.
Will be waiting for this update then.
Cheers

[bigben]

i guess it partly depends on how close you want to get to the terrain but I was thinking of a way to use displacement along the normal to produce your heightfield. Closest I could come up with is...

Convert your DEM to 32bit TIFF (lat/long projection)
Reproject to circular fisheye
Add this image in TG as an image map, Plan Y projection.
Use the image as a function of a displacement shader, direction along the normal

You lose the fractal detail settings available in the heightfield node and there will be some distortion of the elevation data at the extremities but the displacement should be correct which may compensate for that.