Atmospheric and cloud Shading article, written by Oshyan over at Ashundar:
http://www.oshyan.ashundar.co.uk/terragen_detail_settings.html
Creating Micro-Surface Detail in Terragen: [article by Oshyan]
http://www.oshyan.ashundar.co.uk/detail_texture_tutorial.html
Martin Brunker's surface mapping tutorial:
http://www.martin-brunker.de/tutorials/eng_tutorial2.htm
You mentioned that you "get different terrain effects like rocks, or decent-looking grass and snow etc. without changing the colour or bumpiness". Wouldn't this, in fact, be almost impossible? How would you get realistic looking grass/snow without changing the respective color of the surface map? *confused*
As far as making grass, here's what I do... [certainly not the BEST way, either..]
1. In the Landscape Window, click on SURFACE MAP, then EDIT. This will be your foundation/base layer, which means it will cover the entire landscape so I usually make this a pretty default color [say dark gray?] or something that will "coat" the entire terrain. There are no advanced Distribution options for the Bottom layer - save that for the "Child" surfaces.
2. Click on ADD CHILD then EDIT. Here you can create yet ANOTHER surface map, be it grass, snow etc... For instance, when I make "snow" I usually make 3 or 4 "sibling" snow layers in an attempt to make that surface map as realistic as possible. So on the CHILD surface, make the color almost entirely white [or REALLY light gray] with minimal bumpiness and less "mimick terrain". As far as "Depth" keep in mind the units of measurement here.. In "Scale/Depth" you need to decide how far DOWN the terrain this surface map will go, in this case I imagine deeper is better...
If you want, create a sibling layer with the initial snow "Child" layer, but this time, make it a slightly different color, slightly different altitude constraints etc..
When I make grass, I'll do about the same amount of layers - One Child and 3 or so "Siblings" to cover all manner of "grasses" such as lush green grass, semi-dead grass, dead grass, weeds, etc.. Make sure ALL of your "advanced distribution"s are set properly or you'll have equal amounts of lush grass as WELL as dead grass.. Think realistic here.. More than likely there will be [depending on the time of year hehe] more "lush/alive" grass than dead grass, so make sure you properly play with the altitude constraints and max-altitude of each surface map. Bumpiness of my grass textures is also very low...
I find turning the default Gamma Correction at 2.2 a little much, so I always turn it way down to say 1.2 or even just 1 in some cases. [You'll find that option in the RENDER OPTIONS window of the RENDER CONTROL window]
-Others say to render at least TWICE your intended output size then scale down. Example: If you're wanting a 1024x768 wallpaper, render at 2048x1536 then scale in half in any graphics editing program like Photoshop, Corel or JASC's PaintShopPro. As far as I can see, rendering at least twice the needed pixel size, it DOES, in fact, increase the detail of the final image [but only marginally].
If you need more Terragen information, I suggest:
http://www.ashundar.co.uk as a wonderful HELP-filled Terragen community. you'll find all of your answers there.
