Adding/constraining light by altitude -- mountain tops at early morning?

[rcgauer]

Hello....

I am afraid I am not much past the "look what I made it do" stage of learning Terragen... but I have a question that I can't seem to find addressed elsewhere in the forum.

Is it possible to control light strength of low-angle light by altitude, perhaps in the same way I can constrain grasses or snow to an altitude? Or is there another way to do this? The jpg attached is a section of New Mexico mountains from a USGS DEM. I'd love to have the base of the mountains darker/purpler and the very tops lighter/redder.  I can do this with two render passes, and I can do it in Photoshop... but it would be cool to do it in a single solution within Terragen.... Imagine you are watching the light at the start of the day climbing down the mountain side...

Any input and comments welcome.

[Oshyan]

Why not just do this literally with the sun angle and atmosphere adjustments if necessary? Terragen's sunlight and atmosphere modeling is quite good, so you can get some very nice, realistic "light crawling down/up a hill" effects for sunrise/sunset. Just set your sun angle very low, maybe 1-2 degrees, adjust the sunlight heading to be coming from the right angle to strike those mountains, make sure there are no other mountains in the way, and then if the colors aren't right start experimenting with the atmosphere settings, maybe increase redsky decay, or shift its color a little.

- Oshyan

[Dune]

If this only a local dem elevation, you'll have a flat horizon around it. With sunrise (you'll need to position the sun very precisely around the values Oshyan mentioned) you'll get a very straight edge. So for a more irregular edge, add some procedural mountains around this dem, and then of course raise the sun elevation.

[rcgauer]

Experimenting now.... thanks for the heads-up on redsky.