Iges to Maxurf troubles.

[pro_user]

One of my customers have a problem to join surfaces in Maxurf after impot from IGES file. This surfaces have mathemeticaly same boundary, but different number of control points. What to do?

[Andrew Mason]

If they are mathematically identical, you do not need to join them in any way as the edge curves will be coincident. If they are not mathematically identical, then you have two different curves and there is no way of joining them together.

This is why we recommend to people that they don't do hull modelling in programs such as Rhino and use Maxsurf instead. Maxsurf guarantees perfect equivalence between surface edges, other programs tend to do close approximations.

[Tim B]

Hummm, interesting, Andy.

I have cross-checked Rhino against my software and it has a surface deviation (mean) of 1E-15 units. if you would care to send me a full version of Max-surf and I'll validate your comment.

Tim B.

[Andrew Mason]

Tim

I'm not saying that two different NURB modellers are not capable of recreating identical surfaces from a given set of control points. I am happy that Maxsurf, Autoship, Fastship, Prosurf, Prolines, Rhino, CATIA, etc. etc. recreate a given surface to within floating point tolerances.

The question is how you match those surfaces up along their edges. If you have two surfaces whose number of control points along the matching edge, location of those edge control points, knot vectors, surface weights and surface degree are all identical, then the edges will be identical.

Most programs, however, match edges with dissimilar edge properties by using approximate fits. In most cases these fits are very good and yield mismatches of less than 1 mm. However it is not uncommon to get much larger gaps , particularly where the surface parameterisation differs between the two surfaces, resulting in large gaps opening up because of the way the edges are broken down into polylines.

[pro_user]

I have configuration (T-connection) of surfaces like it shown on picture. The common line is exactly same for left patch and two right patches. Is it possible to join it together in Max?