Re: Advanced Surface

This is developing into a very interesting thread. I've already learned a few things particularly with regard to the evolution of Pro/E's tools for dealing with scan data.

Raindrop GeoMagic definitely is not parametric. I will be experimenting with REX next week, but I may have incorporated some parametric functionailty into the process. Raindrop GeoMagic can provide dimensional information in the form of NURBS surfaces that import as dumb solids (no parametrics). Raindrop GeoMagic is in the process of adding more basic geometric constructs (planar surfaces, cylinders, extrusions, etc.), but it was originally developed to accomodate free form scan data and wasn't developed with CAD functionality in mind. PTC is apparently trying to bridge the gap between free form scan data and CAD, but I can't speak to the effectiveness of their tools until I learn more about them.

I'm looking forward to seeing what REX can do. My initial exposure made it look promising, but I suspect it has a some limitations at this point in time. Integrating a free form modeler with a mechanical CAD tool sufficient for detailed design and engineering is a daunting task. I have been looking for such a tool for several years now and everything I've seen has serious limitations. The reverse engineering work I perform includes alot of traditional engineering that software hasn't been able to provide.

Reply to
John Eric Voltin
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On top of the problem I raised with using non-parametric NURBS modellers like Geomagic or Rhino, is the one all of them, including REX, share: they don't analyze geometry for features and where ever possible, give you engineering features or even parametric block primitives. So, you don't have features to modify. How do you change a fillet radius when it doesn't recognize that the part has one? or a wall thickness? or a cylinder diameter? or the length of what you can see started out as a rectangular base feature? This would be the best way to capture para,metrics, the way that Pro/e pioneered. I hope it's working on incorporating this most difficult 'trick' into REX. Maybe Restyle at least gives you some style features. But without being able to analyze conventional, feature based geometry and break it down into features, you're still missing the bridge between NURBS and solids.

On the other hand, if I'm way off base and it actually shines in this area, I'd definitely like to hear about it. I think everyone here would like to hear more about the capabilities of one of PTC's better kept 'secrets' called REX.

David Janes

Reply to
David Janes

David,

I agree with you completely. I'm hoping that REX and/or Restyle helps fill this very large gap. I'll keep you posted...

One of the fundamental problems I see is how do you identify basic engineering features? Should the software make such an assessment without human intervention? Or, should it work in the manner of the Faro and Romer arms that measure the engineering features after being identified by the human operator? Before I had thought about this problem in much detail, I assumed it would be possible for the software to identify features without any operator input. Unfortunately, such functionality would be technically very complex and computationally difficult. Although I don't belive its impossible, this is a very big problem. I understand that Raindrop GeoMagic bought a small company in Europe that was working on this very problem. Apparently, a group of mathematicians was pursuing this problem and Raindrop GeoMagic bought the company to integrate this functionality into their products. When I enquired about this product (almost a year ago), I was told its really not ready for practical use yet. I haven't heard anything further, but I suspect that taking this to a finished/user friendly product is proving very difficult.

Reply to
John Eric Voltin

In my experience, the quality of your point cloud [PC] and the type of geometry in the original form [more primitive or freeform] is the real decider on the best approach for reverse engineering. However much noise reduction [taking out 'outlyers' from a specified tolerance] and fine tuning [thining out your point cloud] of the original PC there is still a tolerance 'thickness' [all points are going to be above or below the original surface] of your PC which could be reflected in your final model. A surface could have ripples which reflect this tolerance.

Once you have a facet file from the point cloud you then get the option to move away from the original data set and 'smooth' out the point cloud. The facet file can then be made manifold - open [closed boundaries] or closed volume [no single sided edges], consistant normals.

Note: REX/facet feature - PC to facet feature. REX/Restyle - facet feature to curves/surfaces.

In REX - Restyle there is a 'best fit' option to create section curves through the facet file, you then use these to create your surfaces - this is fundamentally what you are doing by creating curves outside of REX.

There is an option the create a limited range of primitives from the PC data - rev eng a hole for example. But again, this is only ever going to be as good as the tolerance of your original data.

In experienced hands REX [and similiar software] can save time but don't ignore 'manual' methods and keep an eye on the surface tolerance.

Sean

~~~~~~~~~~~~~~~~~~~~~~~~~~ Sean Kerslake Dept. of Design & Technology Loughborough University LE11 3TU

01509 228317

~~~~~~~~~~~~~~~~~~~~~~~~~~

----- Original Message ----- From: "shaun" Newsgroups: comp.cad.pro-engineer Sent: Friday, February 25, 2005 4:20 PM Subject: Advanced Surface

-- ~~~~~~~~~~~~~~~~~~~~~~~~~~ Sean Kerslake Dept. of Design & Technology Loughborough University LE11 3TU

01509 228317

~~~~~~~~~~~~~~~~~~~~~~~~~~

Reply to
SeanK

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