NURBS topology changes through Image Process

[Britton Ward 0]

Hi,

 

Encountered an interesting problem today that I wonder if you can help me address>

 

Attached project will help outline the steps.

 

Some description for the project:

 

1) I import a IGES 128 surface into Hull -> Surf000

 

2) I create an image of this surface where the only change is I alter the U parameter range for the Image surface.

 

3) Select the image surface and export the iges file and load into a program where you can see the control net layout.

 

4) Create a copy of the image surface and export an IGES file of this surface and load into a program to see the control net.

 

 

The IGES import is a NURBS surface that contains multiplicities and some complex geometry at the bow.  All other CAD programs have no trouble with this topology. [OriginalNet.jpg]

 

The IGES file from STEP 2 retains the initial files topology but is shortened in the U parameter as desired. [imageIGESExport.jpg]

 

 

The IGES file from STEP 4 has reskinned the surface topology completely and lost definition at the multiplicity and at the stem creating an unfaithful copy with significant unfairness.  [CopyIGESExport.jpg]

 

 

If I write my own feature to operate directly on the control points of the s1 surface I am only able to access the reskinned results when I really need the original topology.  Why is it than an IGES export of the image surface retains the topology but the copied surface or a feature accessing it cannot?

 

This is a bit of a showstopper for me at the moment. Hope you have some suggestions.

 

 

Britt

ImageSurfIssue.fdbc

[Mr. Claus Abt 14]

HI Britt,

First  of all, you don't need to switch to another program. You can see and edit the net of pointbased surfaces (and curves) also in CAESES. Select the surface(s) you want to edit and set them into edit mode, see picture.

 

Secondly, I am not quite sure why the first imageSurface's export keeps the multiplicities. Normally Images will be exported as interpolated nurbs surfaces of the rendering positions that you can define yourself, i.e. the U and V resolution. For surfaces with discontinuities I propose to split them into separate images and export them. E.g. transition from flat to curved or maybe the stem and the flat part of the entrance.

We will dig a little deeper and see what we can do.

 

Best regards

Claus

 

[Stefan Wunderlich 6]

Hi Britt,

 

I see the problem.

The copy method for surfaces / curves uses a dumb approximation algorithm (for non-nurbs-types), that has not changed for years.

 

We corrected this for the next maintainance release (which will fortunately be released today).

 

Best regards,

Stefan

[Britton Ward 0]

HI Claus/Stefan,

 

Thanks for your comments.. Claus. ... I new I had seen that edit button before in the environment.. thanks for reminding me.

 

Agree its possible and can be desireable to split surfaces with discontinuities into their own surfaces .. might be an interesting general feature to have to automate it?

 

Even if my surface did not have a discontinuity I would have the problem at the bow however as the reskinning algorithm misses the detail at the bow round and creates unfairnesses.

 

I'll see what happens with 3.1.2 when it is released.

 

Thanks,

Britt

[Mr. Claus Abt 14]

HI Britt,

 

Any advances with respect to your issue using 3.1.2?

 

Cheers

Claus

[Britton Ward 0]

Claus,

 

3.1.2 seemed to fix all the issues I was having! So far so good.

Britt