Yes exactly, at first it may sound like the mimic device but that does much less, it only recreates the curve profile of the terrain and basic roughness, but synthesis tries to imitate whole terrain features
Yes you both misunderstood what terrain synthesis is. It's much more powerful than using any sort of shaping guide currently available in World Machine. For example in this first picture I shared Take a better look at the end result and you can see that it cannot possibly be a result of a normal combiner or perlin shapeguide, because most of the features in the synthesized terrain are completely new. The riverbed for example, in the synthesized result it follows the line of the user sketch but not fully, it bends and meanders just like the river in the style input, the grand canyon DEM.
Now that I read my original post I can see that it can easily be overlooked, but what terrain synthesis does is try to recreate features that look very similar to the style input, but shaped using the shape input.
An analogy would be: you go to your hair stylist and show him a picture of Brad Pitt asking for his hairstyle, he would normally go ahead and cut your hair according to the shape of your head and the type of hair you have, that's terrain synthesis, while what's currently possible in World Machine is going into photoshop, cutting out the hair of Brad Pitt and putting the cutout on your head, maybe with a 50% opacity, but it still looks ridiculous. It's black magic to me, and it would be a gamechanger for me if it was ever implemented into World Machine.
I don't get what part of it is not possible currently, even in the old stable build. You just take a terrain, and a shape, and combine them. Depending on the match between shape and terrain, you can directly use shaping guid in advanced perlin.
Terrain Synthesis is my personal white whale of terrain generation, and an integration into World Machine would bring the software up to a whole new level IMO. If you don't know what terrain synthesis is, here are some examples:
As you can see methods like this could bring World Machine to a whole new level. At the moment the sketch based editing with Layout Generator is very hard to get right, but with terrain synthesis you could achieve very believable and most of all stylistically consistent and accurate results.
Lots of texture artists are already starting to use very advanced synthesis methods to produce lots of new textures from photo reference, especially with the rise of neural networks and machine learning. Here is an example
I know Stephen has probably already an opinion on terrain synthesis in World Machine, but maybe if the community shows some support on this idea he will rethink about it.