Add Curve.PointAtMid() to RhinoCommon?

Rhino Developer
1

Hi,
I might be missing something here and I knwow this has been discussed earlier.

https://discourse.mcneel.com/t/curve-middle-point/18453

Curve Middle Point

As far as I know the only way to get the midpoint of a curve is to use curve.PointAtLength(curve.GetLength() / 2), correct - at least this is what I do.
Would it maybe make sense to add a property to the Curve class, e.g. PointAtMid? At least for me it would save a lot of typing. Even though I could build a small method in my toolbox I always think it would be faster to have this in RhinoCommon and wonder why this is not available there.

Thanks,
T.

2

I think you can use curve.PointAtNormalizedLength(0.5), not sure if you’d say that’s simplier though.

1 Like
3

@Lukxf
This only works with straigth lines, very well described here by @menno.

So I assume the “easiest” way is curve.PointAtLength(curve.GetLength() / 2).

4

I think he speaks of parameter “t” not of the length along the curve

The documentation is clear
https://developer.rhino3d.com/api/rhinocommon/rhino.geometry.curve/pointatnormalizedlength

if it doesn’t work it is a BUG.

5

@laurent_delrieu yes, agreed.
Still this method will be a bit of typing if I am not wrong.
curve.PointAtNormalizedLength(curve.GetLength() / 2)

6

As distance is normalized [0, 1] you MUST use 0.5 to be on the middle.

curve.PointAtNormalizedLength(0.5);

But yes something like

curve.PointAtMiddle;

could make sense, as it was done in Grasshopper.
Long time ago there was just tha component. It that was quite hard to discover, I found it after some months!
image

And as it was quite just used for special case they added this one.
image

2 Likes
7

@laurent_delrieu
Allright, I have to admit I did understand PointAtNormalizedLength quite the wrong way. But I am relieved because it makes me sleep better :slight_smile:
I also came across the grasshopper component quite late and that acutally was the reason I always wondered if there is an equivalent in RhinoCommon.

8

Thanks @laurent_delrieu for clarifying for me!

@tobias.stoltmann these blog posts by @DavidRutten are good for explaining curve parameters:

1 Like
9

Hi @tobias.stoltmann,

Does this help?

import Rhino
import scriptcontext as sc

def __normalized_pointat(curve, s):
    pt = Rhino.Geometry.Point3d.Unset
    if curve and s >= 0.0 and s <= 1.0:
        rc, t = curve.NormalizedLengthParameter(s)
        if rc:
            pt = curve.PointAt(t)
    return pt

def test_curve_midpoint():
    filter = Rhino.DocObjects.ObjectType.Curve
    rc, objref = Rhino.Input.RhinoGet.GetOneObject("Select curve", False, filter)
    if not objref or rc != Rhino.Commands.Result.Success: 
        return
    
    curve = objref.Curve()
    if not curve:
        return
    
    # start point
    pt = __normalized_pointat(curve, 0.0)
    if pt.IsValid:
        sc.doc.Objects.AddPoint(pt)
        
    # mid point
    pt = __normalized_pointat(curve, 0.5)
    if pt.IsValid:
        sc.doc.Objects.AddPoint(pt)
        
   # end point
    if not curve.IsClosed:
        pt = __normalized_pointat(curve, 1.0)
        if pt.IsValid:
            sc.doc.Objects.AddPoint(pt)
    
    sc.doc.Views.Redraw()
    
if __name__ == "__main__":
    test_curve_midpoint()

– Dale

1 Like