A Carbon Cloth can have up to three different meshes as input: Start Mesh, Reference Mesh, and Goal Mesh.
Out of the 3, only the Start Mesh is mandatory.
Let's talk about what each of them actually does:
So, what does the Cloth simulation see when you provide a mesh:
We obviously have the tessellation, i.e. P amount of points and their positions, T amount of triangles (or quads) and their connectivity.
This is all defined by the Start Mesh.
But beyond that, a Cloth has soft constraints, i.e. Stretch, Bend, Surface, etc.
For those soft constraints, we need to extract/build our reference data, meaning each edge has a length, each triangle/quad has a surface area, each edge also connects two triangles (or quads) and we can calculate the angle between those two triangles / quads.
This data is what we call the Reference.
So when you set Stretch Extension to 1.5, you say that each edge cannot extend more than 50% past the length it had in your reference mesh (or Start Mesh if you do not provide a separate Reference Mesh). All subject to convergence, of course.
(Quick side note: Normally, Start and Reference Meshes need to have the same tessellation (i.e. same number of points, triangles, connectivity).
Carbon Tailored mode is a specific Cloth Model in Carbon where you have a 3D welded Start Pose, and a Reference Pose that is made from flat panels, i.e. the number of points is not the same.)
So all the Reference data is extracted from the Reference Mesh. And keep in mind, most of the parameters can be painted as well; the painted attributes must be on the Reference Mesh.
If you do not provide a separate Reference Mesh, we internally just use the Start Mesh.
And then there is Goal Mesh.
This mesh is purely to provide point positions which are used as targets (or goals; hence the name Goal Mesh) for the Simulation.
In theory, a point cloud would suffice, but passing a mesh is easier and ensures the point order stays consistent, etc.
Goal Meshes are only required when you try to Goal Pose a Cloth.
Please refer to the documentation pages about Goal Posing for more information, such as the Goal Pose Tutorial (in the Tutorials/Cloth section), the Avatar Morph Tutorial (in the Tutorials/Morph section), and the Goal Pose / Goal Skin User Guide.
These resources are equally available in the Maya and Houdini plugin.
