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understanding I-Form

NX has two similar surface editing tools: X-Form and I-Form. I can understand X-Form very easily, which simply modifies the difining poles of of a surface.
But I have difficulty in understanding I-Form, which modifies isoparametric curves of a surface. To my knowledge a surface is defined by all its poles, but not by the iso curves. The iso curves are results of the calculation of those poles.
To speak roughly, poles are parents of a surface, and a surface is the parent of its iso curves. You can edit an object by editing its parents. How can you edit an object by editing its descendant? In Alias a command similar to I-Form can't be found.
Thanks for your comments!

Re: understanding I-Form

Gears Esteemed Contributor Gears Esteemed Contributor
Gears Esteemed Contributor

When you create a spline, you can choose the "by poles" or "through points" option. The underlying mathematical foundation is the same for both spline types; but when you create/edit the "through points" spline, you do not see the pole structure. NX takes your input and manipulates the poles for you to satisfy the given constraints. I see X-form and I-form as the surface analogs to the spline's "by poles" and "through points" creation methods.

Re: understanding I-Form


@cowski1   Thank your for sharing your observation!


In editing a "throught points" spline, only those "defining points" specified in the creation process can be modified.


In using I-Form to modify a surface, a set of iso curves can be defined freely first and then played with to modify the surface. It seems to be a little unbelievable because the final pole structure might be crazy. I guess maybe it's for some unique situations.