"Insert Edge Loop" for Polylines and/or Isocurves?

Hi Guys,

I’m pretty new to Rhino and come from 3DS Max. Basically, I have to draw Polylines onto the surface of some dense scanned data, then convert them to Isocurves so the tool I have can work with the data. The problem is that if I need to insert another line, I have to draw it manually as a Polyline then convert to an Isocurve. If there was a way to add another "loop’ like the attached GIF by selecting the edges I would like to add the loop to that would be great. I’m skeptical that such a thing could work on the Isocurves while still following the surface of the scanned data, but if this is possible it would save a little more time I think than doing it as a Polyline and then converting to Iso.

To be honest, I kind of expect the answer to be “no, that’s not how Rhino does things”, but I couldn’t determine this on my own and I need to give my boss a definitive yes or no. Apologies if I’ve asked this in a weird way, left some info out or used an incorrect term, I’m a bit scatter brained these days so bear with me :blush:

Thanks for any feedback you have guys, it is very much appreciated!!


Hello - I am not sure what you mean by this - presumably the ‘dense scan data’ are meshes or points - these do not have isocurves… you’d need a surface to have isocurves. Are you trying to reverse engineer a mesh to surfaces?


Hi Pascal,

Sorry about the confusion. That is correct, the dense scanned data is a polygonal mesh. The only way I could find to draw lines that conform to the surface of the polygon data was to use polylines. Once I have these lines that are on the surface of the data, I needed to convert them using Rebuild so they are usable by a tool I have.

I’m not sure if this is a common term, but my end goal is to re-surface the dense data and create a clean quad based topology more like what you would see in an efficiently made game asset. The tool takes these Isocurves and creates that mesh based on what I drew on the surface. Hopefully that clears things up.

Hello - OK - so just for the record, in NurbsSpeak, Isocurves are curves that are inherent in a Nurbs surface where the parameterization in U or V is constant along that curve - Rhino displays some of these curves as part of the wireframe by default but they are only displayed as curves, they do not exist as independent curves. They can be extracted, (ExtractIsocurve) at which point they are just curves and not associated with the surface any longer…

So, what I think you mean is just smooth Nurbs curves - your deal takes these and can generate a mesh from them that you like? Or does it in fact require a Nurbs surface to generate the mesh (more what I’d expect)?
In any case, to get curves, try the Contour or Section commands and then Rebuild the result - see Help on that command.

Ahh, ok then. Yeah I think I was using the incorrect term then, sorry about that. The edges the tool needs have control points for manipulating the shapes, but they are the object type that is generated by the Rebuild command, if that narrows it down?

I’m not entirely sure what the tool “does” really, but the input is a series of curves arranged to create a grid/quad pattern and from that it creates a denser polygon mesh. It may be creating a NURBs surface in order to get to the end result, but beyond that, it’s functionally a magic black box lol My goal is to optimize the workflow up to the point the tool does it’s thing.