Hello Rhino people. I am wondering what is the major difference between unrollsrfuv and squish. I am trying to unroll two dimensional curve surface, are these the best commands to use ? ,and is there any equivalent function in grasshopper? Thanks
A surface is developable, if it can be “unrolled” into a 2d shape without any compression or expansion.
All developable surfaces are ruled surfaces and are only curved in one direction.
_unrollSrf and _unrollSrfUV are the commands that should be used for those surfaces.
_unrollSrfUV will keep the parametrisation to stay the same as in 3d. This useful for example if you want to _flowAlongSrf later - with the unrolled Surface as a base.
_squish will expand or compress the surface to bring it to 2d. Imagine an elastic piece of cloth or rubber for example…
_squish can be used for meshes as well.
if your surface is curved in 2 direction - you will need squish.
to access this function in Grasshopper you ll need some extension.
for example
hope this helps - kind regards -tom
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Thanks Tom, it is nice and clear !
No !
Unrollsrf will not check if a surface is developable.
below an example of a saddle-like-surface.
it is not developable.
_unrollSrf result in the middle
_squish result at right.
because of the symmetry (mirrored / rotated) of the initial surface, you would expect the same symmetry in the result. - but unrollSrf does not deliver it
squish does.
A surface is developable if its gaussian curvature is 0 at all surface points, see above Wikipedia link.
_curvatureAnalysis can somehow give this information, but the values might be hard to interpret.
_unrollSrf and squish will both report a deviation between 3d and flat version in the commandline.
in above case:
Command: UnrollSrf
One surface unrolled.
Area is 166.5231 sq millimeters (1.24 % ) bigger after unrolling
while squish will report:
Command: Squish
Area: expands 0.011% (3d area is larger)
Compression: average=0.72%, maximum=3.12% (in 3% of pattern)
Expansion: average=0.93%, maximum=3.83% (in 97% of pattern)
1.24% deviation is a failed unrollsrf.
you would expect very very little - maybe something like 0.. 0.01% deviation for a developable surface
curvature Analysis shows
regarding production / cutting-patterns the squish result is preferred and the command offers more control (compression / expansion)
their might be some rare cases where the unrollSrf result is useful - but i think, it s not the intention of the command.
hope this answers your question @Gurgen_Badiryan
kind regards -tom
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