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How to calculate start angle and end angle in ARC for DXF file ?
I am writing a software to generate simple 3D model from point cloud, output of which is also to be exported as DXF. Got struck with the 3D ARC generation in DXF format.
I have three 3D points (P1<x1,y1,z1> ; P2<x2,y2,z2> ; P3<x3,y3,z3>) with which I have to generate ARC and store it in DXF format. So far I am able to generate coordinates for Center (Code : 10,20,30 ), Radius (Code : 40), Extrusion Vector (Code: 210, 220, 230). But not able to find or develop mathematics for start angle and end angle for arc (Code: 50, 51).
Please help me to understand the mathematics behind generating Start and End Angle for ARC.
P.S. I am very new to CAD world.
Thanks,
Yash
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http://help.autodesk.com/view/ACD/2021/ENU/?guid=GUID-0B14D8F1-0EBA-44BF-9108-57D8CE614BC8
50 is start-angle (of a full circle, angle 0 is in east direction in your ocs/210,220,230)
51 is end-angle
between 50 and 51 you see the ARC, both values are stored es radian, so PI is a half circle.
An ARC from 1.57079.. (/ pi 2)
to 3.141592... (pi)
is drawn from North to West (1/4 circle)
Sebastian
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Thanks for the reply, But my question is exactly this, with three 3D coordinates how to calculate values for start angle and end angle (Code 50, 51). I want to know the mathematics behind this.
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I know that this is an old post.
3D Arcs are not AutoCAD entities. Thus, they are not supported in DXF.
Mathematically an ellipse is a conic section viewed perpendicular to the cutting plane. The ellipse's projection is circular when viewed along the cone's axis.
In that context, with respect to a plane perpendicular to the conic axis, a partial segment of an ellipse would be a 3D arc. These do not exist as AutoCAD entities.
Civil 3D Feature Lines can include 3D arcs. When converted to AutoCAD 3D Polylines, the circular arc sections are approximated by short straight-line segments. (Tessellation.)
Christopher Stevens
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