Ellipse and Arc of ellipse in sketches

[DeepSOIC]

I'm very excited to announce that ellipse development branch has finally been merged into the main development branch.
There are a lot of people involved in development. Main work was done by Abdullah. A ton of icons was created by Jim (jmaustpc). A couple of commits and fruitful discussion from Mark Taff (and me); Sebastian (shoogen) helped with git and python; a lot of help with math and geometry from Ulrich1a, DevJohan, Werner (wmayer), Normandc, Ickby; a lot of testing done by Jim, Mark (quick61), Bejant. 100% I've missed someone.

Now, we have support for ellipses and arcs of ellipse in sketcher.
A new concept has emerged: Internal Geometry. An ellipse/arc, when created, is packed with all its goodness (major diameter, minor diameter, foci) available as construction geometry and linked to the ellipse/arc by Internal Alignment Constraints. All of these can be deleted and recreated one by one. Or all at once, with a click of a special toolbar button.
There are two drawing methods available for ellipses and one for arcs of ellipses, all grouped under one toolbar button.
There are no ellipse-specific constraints other than Internal Alignment (which is hidden in the menu). Constraining of ellipses is meant to be done by regular constraints applied to its Internal Geometry or to the ellipse directly.

[NormandC]

a lot of help with math and geometry from Ulrich1a, DevJohan, Werner (wmayer), Normandc, Ickby;

You give me credit where there is none due: I suck at math and only know basic geometry.

Many thanks to all who've been involved in this work!

[quick61]

I think this is another big step forward for FreeCAD. Thank you all and a job well done!

I too had very little to do with it, just did a little testing and watched you guys with a bit envy at the work you were doing. I only wish I could code anything that was even close to this.

Mark

[abdullah]

What can I say... I would not have finished it without you guys, it is certainly a community effort. I have only basic math and geometry knowledge myself, but everybody has put a part of his skills at play here... I think this is pure open-design... for me all of you are equally important from providing user requirements (and that is part of your none Normand), participating in the discussions, giving ideas, solving math problems, contributing icons, testing or doing insane long code reviews... you all make FreeCAD...

[abdullah]

... and much of this work will be reused... Hyperbolic and parabolic arcs and beziers/bsplines will benefit from the created infrastructure... 2015 will probably be a nice year for the Sketcher...

[DeepSOIC]

Lately I've been busy writing some Wiki on the thing, and it's almost done (the essence is). Comments welcome .
Renatorivo was silently helping me by fixing some of my mistakes and uploading a few png's (thanks!!).
There are still a couple of pages missing (Conic sections page and ellipse by three points). Scripting documentation is nowhere near to being complete... But I hope what's in is helpful.

[laurent_parti]

Great option and done simply.

Congratulations, very nice work !

Laurent