How to use ellipticalArc method of AcGiGeometry

[Anonymous]

In custom entity I need to draw slice of cylinder as elliptical arc in subViewportDraw(). I calculated center/start/end points, major/minor radius, normal and tilt angle. I have trouble for calculating the start and end angle from start and end points. I used upvector of viewport for angle calculation. but seems it need diffrent calculation. Can somebody help in this regards?

Thanks

[tbrammer · Accepted solution]

I have attached a small DWG. The red curve is an ellipse.

Start- and End-Angle are measured from the major axis vector inside of the ellipse plane.

So if you rotate the ellipse only the major/minor axis will change - Start- and End-Angle will stay the same.

I think ellipticalArc() uses the same geometric logic. AutoCAD displays angeles in degrees (0-360°). The ARX API uses radians (0-2*pi).

Hope that helps.

Cheers

--Thomas

[Anonymous]

You are correct. I was in assumption that angle should relate to WCS.

Here are two viewports shows my custom entity. other viewport Is just rotated from first. I added calculation to add rotation of view using viewport up vector. But it seems its not required. The blue curve is with added rotation and green curve is fix 0 to 1.5PI.

I will try with fix angle.