Making a brep into a surface

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Permalink Reply by NYCCTfab (Brian Ringley) on July 14, 2012 at 8:17am

A BRep (short for boundary representation) is a 3D modeling umbrella term that typically includes both surfaces and polysurfaces - so if you have an open BRep from a GH loft component, chances are it's a surface. You should be to connect your Loft component output into the S input of an SDivide component to perform the surface subdivision.

If further surface operations need to be performed (reparameterization, for instance) you could always use a surface collection (Srf) component as an intermediate piece in your definition.

It's possible that your open BRep loft output is a polysurface (if your lofted curves are 1 or 2 degrees, if you used straight or developable loft options, etc.) in which case you would want to place a BRep Components (Explode) component between your Loft and SDivide components to break the polysurface down into its component surfaces (they would have to be subdivided separately).

If you want said polysurface to be a single surface (though depending on what you're doing this may not be possible) it would probably be a matter of changing loft options or rebuilding the original curves as 3 degree curves and re-lofting.

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Permalink Reply by Toyin Lawal on July 14, 2012 at 8:31am

Thanks a lot, the problem must have been in the loft. one of the lofted curve is a planer curve, could that be the reason?

there are three curves, two of those three are joined curves (3 curves joined together) and the point of joining of these curves is where the surface is breaking. do i have to fillet the edges or there's another way to achieving this?

thanks

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Permalink Reply by NYCCTfab (Brian Ringley) on July 14, 2012 at 8:59am

I think it's ok to have the planar curve.

Surfaces must be defined by continuous curvature, which is why you can't create a single surface from curves that have been joined (the points at which they meet are discontinuities). Filleting would actually add even more discontinuities as a fillet is just an arc curve added between two curves that would intersect within the same plane.

The best thing to do would be to use the ReB (Rebuild Curve) component in Grasshopper (or run the Rebuild command in Rhino). This would transform the joined polycurve into a single continuous curve with a point count and degree count of your choosing (you probably want 3 degree curves).

There's a little bit of give and take here because rebuilding polycurves into single curves will change your geometry, especially if your discontinuties are kinks and not simply abutted curves with more or lass tangential endpoints - it's just a question of whether or not the change is acceptable within the context of your design.

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