Do Low Quality DEMs Affect Surface Details (ie. Fake Stones)?

[cbshort]

I've been working with a few DEMs since they are giving me the topology that I'm looking for but as I am adding details to the surface, with things like Fake Stones, the details are very rough. For example, I go step by step with the "Wilderness" tutorial to create fake stones and this worked well and as expected, but this was using a fractal terrain.
I attempted the same procedure but with the DEM and the stones end up very splotchy. (See attached images)

I'm aware of the Fake Stones Masking thread but these stones are applied with no other texture other than direct color and should have a similar results as to applying on the fractal terrain.
Are there differences when using DEMs vs fractals or generated heightfields and what could I be doing wrong?

[Tangled-Universe]

The fake stone you have look correct.
Fake stones look like this by default.
What you need is to displace the fake stones using powerfractals.
Additionally you can also stack surface layers or fractals for adding colour to the stones.
Or even use power fractals to add colour and displace at the same time.

The principle of working with fake stones shouldn't differ much when using a DEM or fractal based terrain.
In my experience (and of some others) disabling the "fractal detail" in the heightfield makes using fake stones a bit easier.
The "fractal detail" adds detail to your DEM to "spice it up" since imported DEM's are very smooth.
I can go into more detail about the technical why and how, but at this stage I'd recommend to keep the scene as it is, so not disable fractal detail as well, just to keep things more simple and understandable.

A guideline for displacing fake stones is to displace with a fractal which has a "feature scale" of about 1/3th to 1/2 the size of the stone.
Keep "octaves" of the noise at around 6 to avoid spiky displacements. The "displacement factor" (strength) should be about the same as "feature scale".

Good luck and keep is posted on your progression and questions.

Cheers,
Martin

[cbshort]

Thanks Martin for your response. Your information on settings for fractals is helpful. I am aware that we should be surfacing with fractals, but was just curious as to why there were patchy or non surfaced areas to many of the stones in the default (color to white) settings. It could be the scale that I am in, which  is forcing me to use very small numbers for my stones (2 being as large as I would like to get.)

I am making some progress with a few helpful examples you have provided. I just now need to be able to lower my ocean bed as it is outside my DEM but needs to slope/go lower than 0. Is this possible or do I need to somehow move my DEM base higher (I only need a few meters)
Thanks.
Chris

[Tangled-Universe]

Be aware that the "upper plateau" surface layer is on top of your fake stones layer.
I suppose the "upper plateau" layer is the brownish layer we see.

The reason why this brownish layer is not covering the stones completely is because the surface layer is using the calculated surface provided by the "compute terrain" above it in the network. Despite that the fake stones 'disturb' this layer the "upper plateau" layer is no capable of covering it fully.
You'd need to texture your stones separately.

[cbshort]

The "Upper Plateau" is only to surface the "Green" texture above a minimum elevation so should not affect the stones, as they are distributed via a Surface Layer with Altitude and Slope restrictions so it will only be seen below the green elevation or wherever the "Upper Plateau" is not. The brown you see is the Base Color.

After digesting all the information and mentally working out where things go with the node structure, I was able to get this far (see image), which is getting closer to what I'm after but much more work to be done. Just needed to get a handle on the Stones first.

I still need to deepen my ocean floor so the water isn't less than 1 m deep throughout. If there is a procedure for this without changing the topography above 0 elevation that would be helpful

Chris

[Dune]

You can add some displacement factor (displacement shader, or power fractal, blended by a distribution shader, set at final postion), that moves anything below your coastline lower (with a fuzzy zone of course). The power fractal needs to have an offset as well, or some areas may stick above sea level. That offset will be the main 'mover down'.

[cbshort]

Thanks! This looks promising.
One question, I noticed on your nodes that your heightfield is not connected. In my situation, I need the DEM (heightfield) included and not affected but have the rest of the "world" be the ocean bed but just be a bit deeper. Will this method still apply?

[Tangled-Universe]

His example has a powerfractal called "powerfractal as terrain" which you should consider to be the same as your heightfield.
(a terragen heightfield is also a (2D) fractal terrain, but then restricted to a box)

The powerfractal below is to give the seabed detail.

If you don't want this and want to keep the terrain as is, then replace the powerfractal for a surface layer.
Then in that surface layer set a negative displacement offset, which means "displace the terrain -x metres anywhere this surface layer exists".
Then in the altitude tab set altitude restriction to about the maximum level of your sea, similar to the distribution shader's settings from Ulco/Dune.

[cbshort]

Sounds Good! Thanks!