3D Modeling

[wgreene]

I have body defined in a coordinate system so that the dimensions are quite small.

The parameter ranges for the edges are similarly small.

This causes problems for algorithms that need to manipulate this geometry.

I can use the acis transform operations to scale the body in physical space.

But after the scaling transformation the parametric range is unchanged.

Is there a simple operation I can use to also scale the parameter ranges for the body?

Thanks.

Bill Greene

[Brian]

Bill,

There are a couple of ACIS docs that are relevant:
http://doc.spatial.com/index.php/Scaling_Tolerance_Variables
http://doc.spatial.com/index.php/Tolerance_Variables
http://doc.spatial.com/index.php/Units_and_Sharing_Model_Data
http://doc.spatial.com/index.php/Dynamic_Range

The default values used for tolerance variables in ACIS are SPAresabs = 1.e-6 and SPAresfit = 1.e-3. SPAresfit should correspond to your minimum model feature (e.g., bump, hole) size, and SPAresabs is the minimum separation of two distinct points. If you are working with models that are very small in the units you are using, you should be changing SPAresabs and SPAresfit in lockstep (making them smaller), before doing other modeling operations. This is covered in the first article. This should be done at the start of modeling operations. You didn't state what problems you had manipulating geometry; if appropriate you should first change SPAresabs and SPAresfit, and see if the problem persists.

To answer your question: No, there is not a simple operation to scale the parameter ranges for the body. The curve subclass intcurve has a reparam method, so it is possible to reparameterize some edge geometry; but there are several steps involved.

Hope this helps,
Brian

[wgreene]

Brian,

Thanks so much for the quick reply.

At least I know now that re-parameterization of the geometry is not straightforward.

I should have been clearer about the source of my problem. It is in some

non-Spatial code that I don't even have the source to. I'm just trying to

accomodate some unrealistic assumptions the developers of this code

made about the parameter range. The geometry, itself, came from a

well-known CAD system, exported as a SAT file.

Bill