What's wrong with the opensim heightmap?

[Tess Juel]

The heightmap for the ground of an opensim region is supposed to be a bog standard r32 (32 bit RAW image) file but apparently it isn't; the height scale is off somehow. It's rather weird because the deviation is not linear and it's even different at different locations on the sim.

I first noticed it when I tried to design complete regions with content in Blender and then export to opensim (to SoaS so it's opensim 0.8). That doesn't work since the objects ends up off the ground.

Recently I've been editing ground with L3DT since it has much better terraforming tools than opensim. Again, this makes it hard to edit the ground for regions with content externally.

The one I'm working on right now for example. Max, min and average elevations in opensim are 360.79, 142,21 and 241.85 m respectively.
When exported to L3DT, the numbers change to 360.50, 142.21 and 244.53 m.
Transferring the ground back to opensim with no changes whatsoever, gives me 360.49, 142.20 and 241.84 m.

It doesn't seem like much of a difference but it's more than enough to cause objects that used to sit on the ground to end up either sunk into it or hovering well above it. The average doesn't tell the whole story either since, as I said, the difference isn't the same all across the region; in some palce there's no difference at all in other places it can be several meters one way or the other.

I can't of course be absolutely sure it's opensim that messes up the height map but it's the same problem both with Blender and L3DT and those two seem to match eash other quite well.

[Tess Juel]

Hi Tess,

This can be due to difference in how OpenSim and these other programs store numbers (float, double, long) or there may be some differences in scaling functions.