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isoparametric curves fail on sphere surface

Hi all,


I have created a block and a sphere. Later, I used the sphere to subtract the block. Now I want to create a set of isoparametric curves on this subtracted surface, but NX gave me some unfavorable answers. 


Here are the results when I create 5, 6, 7 isoparametric curves in U direction. 








As can be seen, when I set the "number" as 6, the function gives me unpredicable results.


Is there any one know why? Or is it another bug?









Re: isoparametric curves fail on sphere surface




What I observed is, when you use 'Uniform' and odd number without 'spacing', resultant curves are getting ovelapped as its a semispherical shape.


If you use 'spacing' and low value( e.g.2 or 3), you can see the right result. See what result you get when using Number =5, Spacing =2, and then spacing =360/5 !!


I believe its not a bug.


Best Regards,


Re: isoparametric curves fail on sphere surface

Siemens Legend Siemens Legend
Siemens Legend

This might appear odd but it really isnt. The thing that makes this odd on a sphere is that the sphere is a closed surface, it goes from 0 to 360 degrees in the U-direction.
 If you would have an open surface ( rectangular) and create 5 curves, the first curve would be one of the edges, the last curve would be the opposite edge and then 3 curves in between.

This is exactly the same on the sphere, the first and the last is on the same invisible edge, - the 0 and 360 degree longitude.

 the curves will not start-stop at the northpole-southpole but go all the way around the sphere which means that on the 90 degree position  there will be 2 curves, both the #2 and the #4

  and the same two curves will be on "position 4".
  - on "position 1 &5" there will be 3 curves, ... also the # 3 . ( the middle curve)
 Exactly the same thing happens when you set the number to 6 .




Re: isoparametric curves fail on sphere surface

Siemens Phenom Siemens Phenom
Siemens Phenom

If you toggle on the 'Spacing' option and as you change the value it will also become more obvious as to what's happening when you use values that results in less than 100% of the surface being used as the range for the placement of the curves.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA

Re: isoparametric curves fail on sphere surface


Thanks Tomas.


I believe your explanation is better than mine !