DXF ellipse

[Moouunwalker]

Hi! I have a problem with dxf ellipse ( elliptical arc). I' ve taken the data but can't get correct start angle and end angle. These angles in dxf file are in radians, I convert them to degrees but they aren't correct if I rotate the ellipse. They are also incorrect then end paramater and maybe start parameter is > 2 Pi. There is a formula: p(u)=(Cx+a*cos(u))*i+(Cy+b*sin(u))*j but I couldn' t use it because I get incorrect results. I found a similar problem on this forum but that problem isn't solved. Please help me because I can't solve it for couple of days. Thanks. Here is code from my dxf file:

AcDbEllipse
10
4.515941105878361
20
1.260919452265277
30
0.0
11
0.2648636274097313
21
0.9206522013610863
31
0.0
210
0.0
220
0.0
230
0.9999999999999998
40
0.2244275091508654
41
2.520468679514136
42
7.16461989826817
0
ENDSEC
0

[BillZndl]

In .net,
you don't need any stinking formulas. :^)

You do however, have to take into account, any angle of "tilt" in your axis, from 0.

Bill

[_gile]

Hi,

I'm going to try an explaination with the ellipse you gave the DXF datas.

The ellipse parameters angles are measured about the 'X axis of the ellipse'.
This axis is given by the vector 0.2648636274097313, 0.9206522013610863, 0.0 (DXF codes 11, 21, 31) from the ellipse center.

StartParameter and EndParameter are different from StartAngle and EndAngle:
tan(StartAngle) = tan(StartParameter) * ratio
Where ratio = minor axis / major axis (DXF code 40 i.e. 0.2244275091508654)

Graphicaly (see attached), you can draw the parameters by drawing two circles concentric with the ellipse with radius equals to minor and major radius. The start parameter is given by the projection of the strat point on the major circle parallely to minor axis and the projection of the start point on the minor circle parallely to major axis.

On the attached picture, you can see the start parameter (2.5205) and the end parameter (0.8814). The DXF data for the end parameter is greater than 2 pi because, starting from the ellipse axis and going counter clockwise the angle is 2 pi + 0.8814 = 7.16461989826817

[_gile]

And what about:

Autodesk.AutoCAD.DatabaseServices.Ellipse.GetAngleAtParameter(param)

[BillZndl]

I posted what I did because of this:

Autodesk.AutoCAD.DatabaseServices

Ellipse el = new Ellipse(cenRes.Value, Normal, MajAx.Value.GetVectorTo(cenRes.Value), RadRat, StAng, EnAng);

There is no place for parameters at all.
You can feed the angles from the screen GetAngle picks directly to construct the ellipse.

The only way I can see that you would need the parameters is if you were constructing "Ghost lines" for the ellipse.

Bill