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Ralf Gerlich schrieb:
>> One thing I have noticed, we have alot of urban areas on very steep
>> hill sides. This "draping" approach can cause some very unpleasant
>> visual effects in these instances...the terrain looks ...stretched...
>> like drawing a picture on a piece of rubber then stretching it more in
>> one direction than the other, the picture becomes distorted. Have you
>> noticed this?
>
> Yes. We did some trials with rocky textures on the Zugspitze, the
> highest mountain in Germany (2962m) and we had the same problem.
For special cases like the Zugspitze (or any other mountain top that is
really rough) the best solution would probably be to make an extra 3D
model for it and not to create it with TerraGear.
So the textures can be alinged by hand.
The problem with the automatic texture mapping is, that it can only work
right, wenn the terrain is flat. The less flat it is the worse the
artifacts (texture resolution is irrelevant).
An easy example can be created that shows the problem:
Imagine a nice triangle where all sides have the same length (it is flat
and can have automatically the perfect texture coordinates):
-
/ \
/ \
/ \
/ \
/ \
/ \
/ \
/ \
-------------------
Now cut a hole in the middle and insert three triangles where the sides
also have the same length (this creates a little hill in the middle):
-
/ \
/ \
/ \
/_______\
/\\ //\
/ \ \ / / \
/ \ | / \
/ \|/ \
-------------------
Looking on it directly from above, the texture coordinates are still
easy to find (that's what the automatic code does: an orthographic
projection on a plane). But a soon as you look on the triangle from the
side, the textures on the "hill" are distorted.
You could make "orthographic coordinates" for each triangle. Then the
texture wouldn't be distored anywhere - but between most triangles would
be seams between the texture (which is even worse).
The best automatic soultion I can come up with as the moment, would be
to fit an cylinder (that might habe an infinite radius) through all
vertices that belong to one connected set of one texture type. The
texture coordinates could then be found by a projection from the center
line to the vertex.
This would word great with planes (i.e. like the current apporach) as
well as with gorges / deep valleys.
Special cases (like mountain peaks) are probably best done by hand.
CU,
Christian
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