Removing Control Points from Edited Surface?

I made this original ribbon shape by doing a sweep on a helix. For this shape I need it to cut off at the end the way I have it shown in the picture, but I need to edit that cut off edge where it meets the ground. I cant do this because it is still showing the original control points. I was wondering if there was some way to re-assign the control points to the new surface so I can edit the new bottom edge.

you can only delete complete rows or loops of controlpoints not just a few random

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If you draw 2 helixes, or in fact 1 and a rotated copy, you could sweep a horizontal cross section and create a similar shape that has its control points organized horizontally in U or V
If you need the upper part to say the same, cut it in an area where you don’t need the edits and proceed with the shape I described above to the bottom.

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When trying to use this method, I am experiencing the same issue that I had when I was trying to create this massing in Revit. I am copying and pasting two helices, taking one of them down until it reaches the point I want, and them trimming the piece of it that extends through the ground plane. Then I am sweeping it and I get this. it wants to curve in on itself

if you want a straigth profile, you need an arc as cross section

the arc should have the same radius as the helix.
after rebuild you will have horizontal points to edit:

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What if the helix is not a perfect circle? It is more of an ellipse.

you can make it circular and then use the gumbal to deform it.

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I am still lost on this. How did you make the two parallel helices? I copied and pasted one and then lowered it down to make the ribbon shape and then cut off the part of it that extends through the ground plane. Used the rail as an arc with the same radius as the helix doesn’t seem to be working for me.

I used the rotate command with the option Copy=Yes , then both spirals has the ends at the same high

What do you want to specifically do with the bottom? As was said, you can’t just make those points disappear, that’s not how NURBS work, trimming a surface is actually ADDING to it.

So given that, you have a few options. You can separate out the area you want to change as a separate surface(s) and then blend or match the works up and Join it, or you can point-edit it using the points that are there and just cleanly Trim off the bottom when you’re done. I don’t see any reason to go trying to rebuild the whole helix just to get the points as the bottom oriented differently.

I’m an architecture student, and I am trying to use Rhino to do something that I can’t do in Revit. I need the ribbon shape to be cut off at the bottom along the ground plane, but then I need to be able to manipulate that bottom piece up and out. I am just unable to do this because of the residual control points. I am trying to figure out how to at least make that bottom piece of the ribbon with a flat edge so that I can try to manipulate that and then connect it to the correct looking upper half, but I cannot figure out how to properly sweep that shape with out it having some sort of concave.

Well my point is that you don’t need to make this one surface, just do the very bottom section that you want to “manipulate up and out,” and you can connect that to the rest.

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