Good to see that this has all be thought through- Global scenery rendering certainly is full of pitfalls and it is interesting to compare the different approaches to the same problem!

I'm intending to look more into X-plane scenery development once XP10 is out 🙂

A key difference between FSX and X-Plane is that in X-plane you can't provide land class without also providing elevation, because the base mesh come as one big package.

Alpilotx: if there is a tkae-away thought here it might be that we should provide a second set of .ter definitions with the cliff directives removed. This set of library files would make the base land class texture set available with cliffs turned off, so that authors could control land class entirely ahead of time.

The disadvantage of this is, of course, that the cliff shader does a better job of putting cliff on the right pixels than changing land class, which is a per vertex (not per pixel) operation.

FSX is more like a GIS tool. You feed it different RAW data (yes, of course you need to do preparations) and it fianlly merges them together to form the final visual representation. So, a lot of how the raw data is interpreted lies within FSXs domain. The disadvantage is, that some of these "internal interpretatins" you can't control, and it also eats quite some CPU cycles for sure. The advantage is – especially for scenery developers – that you don't have to care too much about data preparation.
X-Plane is completely different. X-Plane is showing you what you have put into the scenery file (DSF). The DSF file format is really close to the final 3D representation of the data (very closeto OpenGL). The big advantage here is, that X-plane doesn't meddle too much with you base mesh. It takes it how you have created it, and then shows it. So, you have complete control over how that mesh should look (and as a nice side effect, X-Plane doesn't need to spend much CPU cycles here – you have done that at creation time already … and you can spend lot of it at that time). The big disadvantage – for developers – is, that of course you need some quite sophisticated program which translates the different RAW GIS sources to the internal DSF representation. But you also have lots – all – of the control over the mesh you need.
And this is how we build – internally – the Global Scenery. A quite big piece of program, that can eat a lot of different raw data sources, can use rule tables (which we specify/fine tune) and finally spit out the DSF.
So, of course we use a lot of different rules which look at slope angles etc … BUT be aware, that what you seen in this screenshot is only a little part of that system. This "cliff" shading is one of the few "effects" which changes the texturing at runtime (most of it is decided at scenery creation time … this is kind of an override if this helps to understand). But you completely control it! You assign to a bunch of triangles a so called "terrain definition" (well, our tool does that) depending on rules or what ever. And in this "terrain definition" you can place extra rules for the shader (which is working at the runtime of the sim) which might kick in at some slope … or not, if you don't need it (then you just leave that out of the "terrain definition").

So yes, the X-plane scenery system is quite different from what you might be used to …. with its own advantages and disadvantages. But I think it is definitely far more flexible (as in the end you have maximum control over your mesh). And because it is pre-computed, you can do much more time consuming GIS tricks, than a sim can do which need to do this at runtime.

Ideally there should either be some way of turning the automatic slope remapping OFF or to allow definitions of parameters (i.e. slope threshholds, underlying rock types) in a separate file.

Cheers

scnr 😛