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leeminardi
en respuesta a: Kent1Cooper

Kent,

 

"... I concluded in it somewhere that the projection of an Ellipse on the "virtual" face of a cube in isometric is not an Ellipse. .."

 

There are several papers posted on the web that the projection of an ellipse onto a plane does yield an ellipse. Here is one source.

 

I can't say I understand much of the discussion so I tried it out graphically in AutoCAD.

 

The geometry in white in the back row shows a cylindrical cylinder that is sliced with a plane.  After a couple of explodes, you can isolate the intersection and AutoCAD shows it to be an ellipse. The process is repeated but with an ellipse that is extruded and then sliced (green geometry).  Again, the result is an ellipse.  Not necessarily a proof bu it looks like you can say the projection of an ellipse onto a plane is in fact an ellipse.

EllipseProj.JPG

 

The isocircle option for an ellipse (which only appears if you have Isometric snap for grids set) allows you to create an ellipse using the conjugate axes but this is only for regular isometric parallelograms.  It would be nice if it worked for any set of conjugate axes. 

 

~Lee

 

lee.minardi