Steve Baker (steve++at++mred.bgm.link.com)
Mon, 18 Mar 96 22:19:24 -0600
Aha! Not so!!!
----+------------+------------+----
| | |
| | |
| | |
| Square A | Square B |
| | |
| | |
| | |
----+------------+------------+----
| | |
| | |
| | |
| | |
| | |
| | * |
My eyepoint is at the '*'. Now, if the high detail of A is *HIGHER* than the
low detail of B along their common edge, and A were in high detail and B in
low, then the scheme described above would fail - right?
But, I hear you say, A is always further away than B - ergo it's always at
lower detail than B - so no problem.
Well, this would be true if the transition range were always measured from
the center of the squares at sea level - but most modelling tools place the
transition range measuring point at the average of all of the vertices.
Hence, if square B had a *REALLY* high mountain in it somewhere (and yet still
be lower than A at some point on the boundary) then it's transition
range would be measured to a point much higher in elevation than square A
(which could be flat).
So, either generate fill-in triangles for both up and down transitions, or
be careful to force transition ranges to be measured relative to a point
at sea level.
Of course the world is round...so...well, work it out for yourself.
Another point to remember is that you want to force the surface normals of
your in-fill triangles to point more-or-less upwards or else the sun-shading
of your vertical in-fill triangles will produce nasty black blobs in
the terrain when the sun is high in the sky.
The ultimate solution is to morph your terrain between one LOD and the next -
but that isn't as easy as it sounds (although Performer 2.0 makes it a lot
easier).
Steve Baker.
Steve Baker 817-323-1361 (Vox-Lab)
Hughes Training Inc. 817-695-8776 (Vox-Office/vMail)
2200 Arlington Downs Road 817-695-4028 (Fax)
Arlington, Texas. TX 76005-6171 steve++at++mred.bgm.link.com (eMail)
This archive was generated by hypermail 2.0b2 on Mon Aug 10 1998 - 17:52:33 PDT