Dumb question about displacement amplitude

[jdent02]

My question is: is the displacement amplitude in the Power fractal shader in any real world units or just an arbitrary number?  I ask because I have an auto cumulous cloud bank at 7,000 meters and my mountains poke through it in some areas, even though my displacement amplitude is only set to 2,000.

[Kadri]

"The Displacement Amplitude is one of the most fundamental controls on this tab.
It controls the actual level of displacement of the surface – i.e. how "tall" the features will be.
The actual size of the features is controlled by the scale of the displacement function, in this case on the Scale tab of the Base Colours node.
The Amplitude is measured in meters, the default Terragen 2 units. By default it will be at 1, which will barely be noticeable. "

From here:
http://planetside.co.uk/wiki/index.php?title=Surface_Mapping_and_Shading

[jdent02]

"The Displacement Amplitude is one of the most fundamental controls on this tab.
It controls the actual level of displacement of the surface – i.e. how “tall” the features will be.
The actual size of the features is controlled by the scale of the displacement function, in this case on the Scale tab of the Base Colours node.
The Amplitude is measured in meters, the default Terragen 2 units. By default it will be at 1, which will barely be noticeable. "

From here:
http://planetside.co.uk/wiki/index.php?title=Surface_Mapping_and_Shading

This wasn't quite what I meant by the Power Fractal shader, I was talking about the main terrain elevation generating PF in the terrain node group.  My base color node isn't actually contributing any displacement (the option is unchecked).  I checked the elevation of the mountains I was talking about and they were over 18km in height even thought the displacement amplitude of the PF was only set at 2,000.  When I dropped the amplitude down to 500 I ended up with 8km high peaks, which is tall but not completely absurd.

Edit: I think I figured it out.  The lead in scale setting does interact with the amplitude slider, as increasing the lead in scale makes everything taller, and I have to dial back the amplitude slider to compensate.  So basically the amplitude slider is not technically in meters.

Thanks for the pointer Kadri.  It wasn't exactly what I was looking for but it pointed me in the right direction.

[WAS]

"The Displacement Amplitude is one of the most fundamental controls on this tab.
It controls the actual level of displacement of the surface – i.e. how "tall" the features will be.
The actual size of the features is controlled by the scale of the displacement function, in this case on the Scale tab of the Base Colours node.
The Amplitude is measured in meters, the default Terragen 2 units. By default it will be at 1, which will barely be noticeable. "

From here:
http://planetside.co.uk/wiki/index.php?title=Surface_Mapping_and_Shading

This wasn't quite what I meant by the Power Fractal shader, I was talking about the main terrain elevation generating PF in the terrain node group.  My base color node isn't actually contributing any displacement (the option is unchecked).  I checked the elevation of the mountains I was talking about and they were over 18km in height even thought the displacement amplitude of the PF was only set at 2,000.  When I dropped the amplitude down to 500 I ended up with 8km high peaks, which is tall but not completely absurd.

Edit: I think I figured it out.  The lead in scale setting does interact with the amplitude slider, as increasing the lead in scale makes everything taller, and I have to dial back the amplitude slider to compensate.  So basically the amplitude slider is not technically in meters.

Thanks for the pointer Kadri.  It wasn't exactly what I was looking for but it pointed me in the right direction.

Amplitude is procedurally generated by the PF via the Scale, Lead-in, and Smallest Scale which together plug into the fractal algorithm to give us our PF. Then the amplitude makes it's best guesstimate as to what the amplitude is based on your "multiplier" and the elevation perceived from the PF map. It's the same in Game Design and the texture of a Image and it's Sharpness contributing to Bump Map settings. Which is why every texture needs tender love and care. xD

[Tangled-Universe]

Displacement amplitude is in TG units and TG units are in meters where applicable.

The displacement amplitude acts as a multiplier on the fractal output.
So anywhere where your fractal is white the displacement will be at its maximum.

A possible reason reason your mountains exceed 2000 meters in altitude is because some of the settings in the PF makes the PF generate values > 1.

[WAS]

Displacement amplitude is in TG units and TG units are in meters where applicable.

The displacement amplitude acts as a multiplier on the fractal output.
So anywhere where your fractal is white the displacement will be at its maximum.

A possible reason reason your mountains exceed 2000 meters in altitude is because some of the settings in the PF makes the PF generate values > 1.

I wonder if that amplitude is just that, amplitude, a multiplier, and nothing to do with meters. Meters are perceived after final calculations by the preview and other tools. Because I've done a solid white surface, with a displacement of 1. That should be 1 meter, but the surface may be higher, then 1 meter if you disable displacement all together. I'll have to look again to see if there were other settings taking effect.

[Oshyan]

It's measured in meters, but there are other factors determining the total height range.  I'll try to have Matt elaborate on that when he gets a chance. I don't know that the other factors explain the variances you're seeing, but unless you're testing in a totally basic situation with *just* the Power Fractal providing displacement, then it's not really useful data anyway.

- Oshyan

[Tangled-Universe]

Displacement amplitude is in TG units and TG units are in meters where applicable.

The displacement amplitude acts as a multiplier on the fractal output.
So anywhere where your fractal is white the displacement will be at its maximum.

A possible reason reason your mountains exceed 2000 meters in altitude is because some of the settings in the PF makes the PF generate values > 1.

I wonder if that amplitude is just that, amplitude, a multiplier, and nothing to do with meters. Meters are perceived after final calculations by the preview and other tools. Because I've done a solid white surface, with a displacement of 1. That should be 1 meter, but the surface may be higher, then 1 meter if you disable displacement all together. I'll have to look again to see if there were other settings taking effect.

The way it should work - otherwise it's also too complicated to wrap your head around it anyway which is a different discussion of course - is that where the fractal is pure white it has a value of 1.
Then the displacement amplitude, if it is set to 100, creates 100 meter "high" shapes where the fractal is pure white and has a value of 1. (given it is clamped)
That's where my "multiplier idea" comes from.
I never understood it to work differently anyway.
Classically fractals generate values between -0.5 and +0.5, but I believe Matt changed this in TG for easier understanding.

Factors like noise variation and displacement roughness/spike limit can create unexpected stronger displacement.

For example, set noise variation to -2. Some stuff will go sky high.