compute terrain patch size confusion

[Nala1977]

so im quite confused on what to use, when to use and why to use some different values for the compute terrain patch size.
anyone have any clue or explanation on the desired output?

these are 2 renders one with compute terrain 1, and other with value of 20, there is a slight difference but it looks like the value of 1 gives more details, or am i wrong?

how do you approach on how to use this setting?

[WAS]

Compute Terrain is like computing the normals of the terrain. It allows things to conform more accurately to terrain geometry, such as lateral displacement or surface layer constraints. If you're up close to the ground, and small rocks and displacements, you'll want a smaller patch size. If your terrain is distant, you could get away with larger patch sizes, and simultaneously quicker renders in some cases.

Take a look at these examples I've provided. First shows how a patch size of 20 will provide inaccurate height limit results (right side) while the left side is more accurate to terrain height with patch size of 1.

The next example shows the difference of lateral displacement at a small scale.

[Kevin Kipper]

As Jordan has pointed out, the Patch Size informs Terragen of the distance between sample points.  The lower the Patch Size value the closer the samples are in relation to each other, therefore more samples are calculated for a given area, which of course can take longer to calculate.

The Patch Size value can also be used to customize masks when using "Get" nodes as seen in this tutorial under the section titled "How the blue function nodes work".:
https://planetside.co.uk/wiki/index.php?title=Masking_with_Get_Nodes

[WAS]

As Jordan has pointed out, the Patch Size informs Terragen of the distance between sample points.  The lower the Patch Size value the closer the samples are in relation to each other, therefore more samples are calculated for a given area, which of course can take longer to calculate.

The Patch Size value can also be used to customize masks when using "Get" nodes as seen in this tutorial under the section titled "How the blue function nodes work".:
https://planetside.co.uk/wiki/index.php?title=Masking_with_Get_Nodes

Well that's certainly fancy. Hadn't seen that. So similar to the intersection for favoring depressions or rises but a little more exposed to work with for functions.

[Dune]

There's a mistake in the lines under image number 4: "Repeat these steps to add nodes for "Get altitude in Atmosphere", "Subtract scalar" and "Colour adjust ". When you're done the ......."
There is no 'get altitude in atmosphere'.

Also, for a lot of renders, a compute terrain can be disabled. Saves render time. I use it sparingly.

[KlausK]

I guess that should be the "Get Altitude in Texture" that is seen in the screenshot.

CHeers, Klaus

[Kevin Kipper]

Thanks Dune for pointing out the mistake in the wiki docs.  Fixed.

[WAS]

Also, for a lot of renders, a compute terrain can be disabled. Saves render time. I use it sparingly.

There are instances where this could be done, yes. But if you are using things like intersection zones, lateral displacement, close up fake stones, you'll need it.

A super distant terrain could definitely benefit from just a texture coordinates for texturing when you're not close to even look at the displacement (think mountain silhouette).

Additionally, you can merge in the compute terrain similar to my example, giving you computed terrain up close for fake stones, lateral, etc, and none far away to speed up distant rendering and things that don't need lateral/complex fake stones, etc.