[cad-linux-dev] Re: thing'd-foo

  • From: Bruno Postle <bruno@xxxxxxxxxx>
  • To: CAD linux development <cad-linux-dev@xxxxxxxxxxxxx>
  • Date: Mon, 23 May 2005 11:17:59 +0100

On Sat 21-May-2005 at 12:09 -0700, Eric Wilhelm wrote:
> But wait.  Arcs are still circles, they just have those 'angles'
> thingies.

..but surely circles are just ellipses with eccentricity = 0 and 
ellipses are just a class of conic sections - You could devise a 
data storage class that did arcs, circles, elliptical arcs, 
parabolas etc...  all at once.

However, sometimes it is really useful to think of a circle as a 
point with a radius or as three points or as two points and a bulge.  

If you are doing parametrics then that is exactly the kind of 
variation you need.  For example, the centre-point of a circle might 
need to be a reference to a node in a polyline and the radius might 
be equal to the text content of a text entity - Difficult to layer 
this stuff onto a conic-section super class.


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