Rhino API's `Arc.StartAngle`

Scripting
1

When attempting to write Arc.StartAngle using the Rhino API, consistently returns zero. Is this the expected behavior?"

2

Hi @Shital_Naphade,

You might consider sharing some code that isn’t working for you.

– Dale

3

We are using the following code and getting startAngle value always zero.

if (geometry is ArcCurve)
            {
                ArcCurve arcCurve = geometry as ArcCurve;

                Point3d center = arcCurve.Arc.Center * scale;
                Point3d startPoint = arcCurve.Arc.StartPoint * scale;
                Vector3d radiusVector = new Vector3d(startPoint - center);
                Vector3d normalVector = arcCurve.Arc.Plane.Normal * scale;

                double startAngle = arcCurve.Arc.StartAngle;
                double endAngle = arcCurve.Arc.EndAngle;
            }
4

Hi @Shital_Naphade,

In Rhino, an arc consists of:

  1. An oriented plane
  2. A radius
  3. An increasing interval with the start and end angle in radians

In most cases the starting angle (Interval.Min) is 0.0, which indicates that the arc begins at a point on the plane’s x-axis at the specified radius from the plane’s origin.

Hope this helps.

– Dale

5

Is there any Rhino API available for writing an arc using the center, start point, and angle?

6

Hi @Shital_Naphade,

You might start with Arc constructor that has this signature:

Arc(Plane plane, double radius, double angleRadians)

An arc’s start point falls on it’s plane’s x-axis. Thus, the input plane should be oriented in this manner. The center point of an arc is it’s plane’s origin. The remaining parameters should be obvious.

Does this help?

– Dale

7

Thanks for the suggestion.
I have one more query: Even if we pass the angle in radians, such as 1.57, in which direction will the arc be created? (Clockwise or counterclockwise?)

8

Counterclockwise if the value is positive, clockwise if the angle is negative.

1 Like
9

If we provide a positive angle, it still rotates in the clockwise direction.

Arc code
Arc code863×430 11.9 KB

Arc
Arc1008×778 48.9 KB

10

Check the orientation of your plane’s Z axis…. It’s probably the inverse of what you think.

11

Thanks for your help, the problem is resolved.