Richard, thank you a lot for your answers. I was searching around on the forum and your answer seems to be the most complete information on geometry shells.
Nevertheless can someone fill in the specifics of those points?
There are still quite some things that I am not sure I completly get the idea how it works.
A geometry shell gives a second copy of a figure, matched to the current pose of the figure though it can be moved around the scene.
From other software applications I am familiar with the term “instances”.
As far as I understand it an instance is a duplicate of an item allready in the scene.
The geometry and material of the instanced item in most cases cannot be edited.
Nevertheless the instance can be moved around.
This is different than having making a copy of the item. If a copy of an item is placed in the scene the polygon count doubles.
On the other hand adding instances of an object to the scene does not raise the polygon count because the geometry of the original is reused.
The idea behind this is that a scene can be populated with a lot of intances of the same object while the actual polygon count of the scene remains the same.
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So it seems the gemetry shell is different from an instance in regards that the material of a geometry shell CAN be edited.
But I still do not quite understand HOW that really works.
A shell can have different settings from the master figure, and can have a push modifier applied.
Thats the first point where I stumble.
What or where is the push modifier?
Is it the same as the “Mesh Offset” that can be adjusted in the paramters tab?
Default seems to be 0.10cm.
It can be used as a collision target, to increase the offset (once a push modifier has been added).
I guess this will make sense as soon as I understand what exactly the push modifier does.
I asume this could be useful for dynamic clothing or when layering different clothings on top of each other.
or it can have a second skin applied to make clothes or body hair, or it can be moved elsewhere in the scene, with new materials, to add crowding without as much resource use as a full figure, .
From that I gather that the geometry shell is indeed an advanced “instance”.
The geometry shell does have material zones. Instance Nodes do not have material zones.
Is there anything a instance node can be used for that the gemoetry shell cannot do?
Or to put it different what are the occasions where it would be more useful to use instance nodes instead of a geometry shell?
or it can be used as an occlusion shield - set to be visible to AO but not otherwise to render, with transparency maps removed, so that you get faster renders with at least approximate AO from hair.
A possible use for this is explained in this thread:
Hair Tutorial for DS4 Users
Nevertheless I still do not understand:
What is the interaction between “rays” from raytracing a gemeotry shell and the original gemetry below?
Do “rays” from raytracing pass through the geometry shell or not?
Is the idea of adding a “geometry shell” on top of the geometry that all rays are blocked by the geometry shell?
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I see that the geometry shells can have transparency / opacity settings.
Are they affecting only visibility but not if rays pass through?
If I add a transparency map or opacity map will the “rays” go through the geometry shell and then calculate the interaction between the orginal geometry and the “geometry shell”? Or are rays blocked completly at the shell?
Is there a setting that deceides if rays pass through the gemetry shell or not?
Or is the main definiton of gemetry shell that no “rays” pass trough at all in any cases?
To put it different is that technique with fantom hair only usefull for hair that has “transmaps”? But on the other hand for fiber mesh hair without “transmaps” there is no added value by adding a geometry shell? Or am I missing a point?
Is the idea of “geometry shells” in this use the same as puting on a tinfoil hat on ones head so alien rays cannot enter and read ones thought?
Or course now the whole idea of the tinfoil hats may indeed actually not work. But who knows…