# Command: _CreateUVCrv

Hi all.

In the helpfile about Command: _CreateUVCrv

http://docs.mcneel.com/rhino/5/help/en-us/index.htm#commands/createuvcrv.htm%3FTocPath%3DCommands|Alphabetical|C|_____66

Note: The control polygon determines the sizes of the uv curves.
Do you know whatâ€™s the meaning of this?

In the attached file:
Command: _CreateUVCrv and then Command: _Length
U line length = 26.2393
V line length = 22.096

Why is this U line length = 26.2393 and V line length = 22.096?

vs

Command: _ExtractControlPolygon and then Command: _Length

However the length of control poygon did not same with length of UV line.
What is the reason?

Hi Knead - I believe the phrase

Simply means that the overall rectangle that is unrolled will be determined by the underlying surface and not the trimmed face. Does that clarify things?

-Pascal

Unroll? But, It is not developable because it is doubly curved.

Hmm, Sorry but i can not understand it.
Would you please attach the example 3dm file?

CreateUVCrv_UnderlyingSrf.3dm (72.2 KB)

Does that file help?

-Pascal

In the CreateUVCrv_UnderlyingSrf.3dm:

The overall rectangle UV curves:
U Length = 262.213 millimeters
V Length = 206.779 millimeters

Are these UV length (Maximum or Minimum) of the underlying surface edges or isocurves?

I want to know how to the calculation of UV length manually from the surface.

These are the surface edge lengths in parameter space - the 3d edge curves may well be and usually are, different. You can untrim the surface and measure the edges to check. As far as I know there is no reliable way to know the dimensions of the UV curves from the surface.

-Pascal

Thank you Pascal