Tangent to a Brep

Grasshopper
1

I want to find two tangent lines to a given brep which pass through a specified point.
It is easy to draw these lines on rhino by command _line _Tangent.

I made a GH which can find the tangent lines (see the attached file). But any components (or plug in) can do the same thing?

1 eng
1 eng1920Ă—1080 380 KB
GK 312C.gh (14.7 KB)

2

image
image1360Ă—735 67.1 KB 

  private void RunScript(Curve curve, Point3d point, double seedParmameter, ref object A)
  {
    double t;
    curve.GetLocalTangentPoint(point, seedParmameter, out t);
    A = curve.PointAt(t);
  }

LocalTangentPoint.gh (14.2 KB)

3

Dear Mahdiyar, thanks a lot!
I encountered a problem. Please see the attached! What should I do??

2
21333Ă—750 136 KB

4

It seems you’re using Rhino 5, This script supposed to work on Rhino 6.

5

This one must work on Rhino 5 too:

private void RunScript(Curve curve, Point3d point, double seedParmameter, ref object A)
{
    var c1 = (new Circle(point, 1.0)).ToNurbsCurve();
    double t1;
    c1.ClosestPoint(curve.PointAt(seedParmameter), out t1);
    Line l;
    Line.TryCreateBetweenCurves(curve, c1, ref seedParmameter, ref t1, false, true, out l);
    A = curve.PointAt(seedParmameter);
}

IntervalSelection
IntervalSelection1400Ă—714 65.9 KB

IntervalSelection.gh (25.6 KB)

1 Like
6

Dear Mahdiyar
Yes, I use Rhino 5. I can execute your new script now. Thanks a lot!

7

Here’s a less accurate way without scripting:

image
image1943Ă—521 37.3 KB

20_04_07_tangent_to_curve_mrtn.gh (7.3 KB)

8

hi, can you explain to me what is the “seed parameter” in that method? I tried to change the “seed parameter” from 0.0 to 1.0 and cannot see the difference. Thanks.

9

There might be some situations where there is more than one tangent line available. This function uses seed parameter to find the desired tangent point.
Seed
Seed.gh (21.7 KB)

4 Likes