Adding Control Ponts to Curves Without Modifying the Path

Rhino
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1

Hello,

I am trying to create a curve that bends up to a point in the middle and then goes back down. This is for a roof profile, so I need the line to be perfectly straight and have no variation. I have tried using Rebuild to add more control points in order to move these control points up, but when I use Rebuild, it modifies the path of the cirve slightly which will not work for me.

The end goal is having a curve that slopes up to a point in the middle so that I can use Sweep2 to create a roof surface that follows the curve. I have attached a screenshot of our preliminary model showing the roof shape that I am trying to achieve.

Screenshot 2025-02-11 111329
Screenshot 2025-02-11 1113291066×287 8.56 KB

2

Rebuild is not for adding control points to a curve, it’s mostly for completely resetting the structure of a curve for future point editing.

Use InsertKnot to add control points to a curve without changing its shape.

3

I did try InsertKnot, but when I use it and drag the points up, it creates straight lines inbetween the new points. I need the curve to be an organic shape.

4

So you’re starting with straight lines? Post the curve please.

5

The white curve on the bottom is the starting curve. I essentially want that curve to follow the path of the blue points shown.

Screenshot 2025-02-11 113858
Screenshot 2025-02-11 113858744×316 33.5 KB

6

Very strange behavior.

Post a .3dm file with the curve. It is difficult to diagnose anything based only on a screen capture.

7

Here is a dropbox link to the 3dm file.
https://www.dropbox.com/scl/fi/oklocuczz261mwzblbdln/250210-SOUTHWATCH-ROOF-RHINO-MODEL.3dm?rlkey=baroh0gi4zzey545nsadezhni&dl=0

8

Looking at the image further it appears the curve may be polycurve with two line segments and an arc/fillet. If so then inserting knots into the line segments and moving the resulting control points will result in behavior you see.

9

You can upload the file into a post by clicking on the vertical arrow icon above where you type a post.

Assuming a polycurve with straight line segments and arc:
Copy the polycurve.
ChangeDegree the polycurve to degree 3. If more control points are needed then use InsertKnot. Move control point to achieve desired shape.

The planview shape of the arc may change slightly. To maintain the exact planview shape then vertically ExtrudeCrv the original polycurve. Pull the modified curve onto the extruded surface.

10

Could you use an edit point curve?—-Mark

11

Edit points are an alternative way to change the shape of curves. Edit points can be turned on for alll NURBS curves in Rhino. The number of edit points for a curve is the same as the number of control points.

Using edit points instead of control points to change the shape of the curve would not help in this instance. More control points are needed, and the line segments need to be changed to higher degree curves.

12

How about Change Degree?

13

I recommended ChangeDegree in a post #8.

1 Like
14

Hi @Joe_Seelhammer
I’d probably use Crv2View, which is history enabled, so you can adjust the precise slope after seeing the result of your plan and elevation.


HTH, Jakob

1 Like
15

This ended up being the solution. Change degree + InsertKnot gave me the result of keeping the planview shape perfect while having enough control points to make the shape. This project has been endless headaches on the modeling side of things since the client decided they wanted to go with this roof shape and I appreciate the throrough help. Thank you!