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surface types


Duckman
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Mastercam allows you to create three different types of surfaces: Parametric, NURBS (Non-Uniform Rational B-Spline), and Curve-generated. Each type uses a different method to calculate and store mathematical data about the surface. NURBS is the default one. When you analyze the surface it gives only this info not how you generate the surface (revolve, coons, draft, etc)

 

[ 07-31-2002, 11:02 AM: Message edited by: Mariana Lendel ]

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Guest CNC Apps Guy 1

There are two CORE options for creating surfaces. NURBS and Parametric.

 

NURBS - Non Uniform Rational Bezier Spline

 

When analyzing a surface you'll only get what type of surface (i.e. NURBS, Trimmed NURBS, and Parametric).

 

Hope that helps.

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Duckman,

James is misleading you a bit. As Mariana said, several surface types can be optionally be created as "curve-generated". For instance, a Revolved surface can be made as either a NURB surface (NB_SURF), a Parametric surface(PP_SURF), or a 'curve-generated' Revolved surface(REV_SURF). Ditto for Ruled & Lofted Surfaces (NB_SURF, PP_SURF, or LOFT_SURF) and Draft Surfaces (NB_SURF, PP_SURF, & TABCYL_SURF). They're called curve-generated because all that gets stored in the database are the curves used to generate them and a few parameters. They are exact representations that are much smaller in the database and much faster to perform evaluations on. The ONLY downside to them is that they will be converted to NURB surfaces (and sometimes it's an approximation) when exporting to IGES, and Parametric surfaces when exporting to VDA. They will also become NURBS when used in anyway in Solids.

PDG

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From this can I infer that NURBS surfaces are not exact representations? If I wanted to intersect a plane with a spherical surface, and the surface is NURBS, I get a spline that approximates the circle of intersection but is not exactly cicular. If my surface was a revolved surface, would I get a circular arc of intersection? (I will experiment with this right now...)

 

Thanks for you help!

 

okay tried it, and I still get a spline...so I am unsure about the exactness of a REV_SURF

 

[ 08-01-2002, 10:15 AM: Message edited by: Duckman ]

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Duckman,

It's the intersection code that is causing the approximation. Your REV_SURF is exact. A NURB surface representation of a Revolved surface will also be exact (at least via our X2Nurbs function). The intersecting & slicing algorithms simply march along the surface gathering points so that there is not more than the desired deviation between the resultant curve and the original geometry. That's why Screen/Config has a 'Maximum Surface deviation" value.

PDG

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  • 19 years later...
1 hour ago, jean said:

OK, what about if you have NURB surfaces and when you try to convert to solid the surfaces disappear? How do you fix that?

 

Thanks in advance, 🐱‍🏍

Make sure that delete surfaces is not checked in the create solid from surfaces creation box. Other than creating a copy on a different level if that is not helping not sure what to say.

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1 hour ago, crazy^millman said:

Make sure that delete surfaces is not checked in the create solid from surfaces creation box. Other than creating a copy on a different level if that is not helping not sure what to say.

Yeah I'm aware of the delete/Keep but not really aware of "Blank"

I figured out why is was disappearing! I had my levels off......🤦‍♂️

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