Playing with the Planet material combiner, here is some info: (Looks like I will have to isolate some of these to see what they really do)
Feature Size is how large the features are.
This is not keyed to how large the model or patches are, so a "physically" large model will need larger values to get actual land masses and not a whole mess of tiny islands. The number of patches has no bearing on the calculations, in fact my station renders the same surface with 64 patches as it did with hundreds.
Polar Distance is what the ice caps cover. It is the distance from the equator in cm, a value of 0 turns this off.
It appears to be along the surface, not the y-axis. It really should have been an angular measure, as the icecap would depend on how the planet rotates in relation to its orbit; a percentage would heve worked too. As a reference, if you set your PD = to the planets radius you get about a 31 degree coverage.
Water primarily affects the elevation of the water. Not sure whether it is a percentage of the amplitude, but it is easiest to treat it as such.
The best range seems to fall between 20 and 80; below 20 is barren and over 80 is waterworld. This does affect vegetation and snowcap generation.
Bump Strength is surface roughness, as a percent, as is standard in AM
Ice is a percentage of coverage to the equator. It has 2 big effects, adding ice to snowcaps and ice to icecaps. A value of 0 turns it off.
Frequency Factor is similar to roughness, it appears to be the underlying surface that is modified by roughness, amplitude, and octaves.
Amplitude Factor is a percentage. Appears to act like roughness or frequency factor.
Octaves alters the waves generated by Frequency and Amplitude
Noise Factor adds chaos to some of the other generators, it is most noticable in Polar Distance and Ice.
Seed is used to generate the terrain and allows the terrain to be generated in the same way with a certain selection of settings.
Offset is a percent, looks like it shifts the median up and down, affecting terrain generation.
Mottle Size affects how fine or coarse the generated color map is
Higher numbers mean larger clumps means coarser, lower is opposite
Mottle Magnitude ?? it is a percentage
Depth Noise another percentage, uses the terrain that is underwater to affect the shading of the water.
Max Depth caps the values for water depth?
Snow the last percentage. Affects snow coverage, works in conjunction with Polar Distance and Ice to provide coverage
The material does not generate a displacement map, and in most cases I would agree that it would be overkill, and I may just go with bump maps after I block my shots.
Wish it had a seasonal adjustment, thought that was what snow was going to do, but no. A seasonal would shift the north and south hemispheres in opposition, with the middle being spring/fall, one end would have summer in the north and winter in the south, the oppositer end would swap the seasons. This can be done manually, actually, if you seperate your north and south hemispheres and apply a copy of the materials to each, you can shift your snow/ice coverage and move your icecap towards the equator.
Now to bake it.