Im having trouble with what seems to be a basic problem: I got a geometry and want to cut the lines at the intersection of a line I projected onto the geometry (to cut out the right hand side of the model in the pic).

Hi Jan,
Your approach is right, it’s just that your U and V curves are coming out of the shatter in opposite directions. Here are a couple of ways to fix it, either process them separatly, or flip the directon of one of the sets of curves.
I hope that helps,
Drew

Thank you @Drew for internalizing the geometry for us R5 folk. This might be a case where R5 and R6 give different results? One little tip to keep the file size as small as possible: re-use one internalized copy of the geometry instead of duplicating the internalized params.

@jan.de, at first glance it appeared that your “cutting curve” was planar, but it’s not? Still, I couldn’t resist playing around with using a plane to slice both your curves and a surface lofted from them.

The purple group at the bottom uses three points on your cutting curve to derive a cutting plane.

The blue group lofts your vertical curves to create a surface, then slices it with the plane.

The white group uses the same plane to cut both Horizontal and Vertical curves.

In the white group, there are three Preview components. The white color shows curves that don’t intersect the plane and remain untouched. The green color shows the split part of the curves covering the hole. The yellow color shows the split part of the curves NOT covering the hole.

Likewise in the blue group, the green Preview shows the split surface covering the hole, the other (blue) shows the surface that remains.

So disabling both green group previews hides the hole.

With your Rhino file open, right-click on your Geo params and click “Internalize data”.

It’s covered in #3 on this list:

I don’t quite understand that, would need to see how it’s done? It’s not planar but close, as you can see below by comparing your curve in blue with the plane intersection curve in yellow. They differ by a maximum of ~0.3 units.

Aha! In fact, your curve is derived from projecting a circle, not an ellipse, onto the lofted surface. See cyan group below. Rewired to ditch the Plane Fit and use the projected circle instead. The projection results in three curves, not just one, hence the need for List Item to choose which one. The “two openings?” panel instead of “1” will cut the same arch in opposite sides; it works on the surface and horizontal curves but doesn’t split the vertical lines at the second opening. Not motivated to fix that at the moment.

Oh very cool. Sorry I didnt get to reply you earlier but I guess you figured it out yourself. Thats pretty much the same script I use. Thank you for your input. I will try to add the possible second opening later. You are also right, while I use the ellipsis function, both parameters are the same in the given picture so it’s a circle.