Geometry

[lrdheat]

After making an ellipse in geometry app, how do I use measure to get it's area? I keep getting zero! I'm not getting this...!

Thanks! (The geometry app looks like fun).

[Fortin]

(01-01-2016 09:07 PM)lrdheat Wrote:  After making an ellipse in geometry app, how do I use measure to get it's area? I keep getting zero! I'm not getting this...!

Thanks! (The geometry app looks like fun).

It returns 0 for me as well.

The help for area() does not mention anything specifically about working for an ellipse. It does mention and returns non-zero results for circles however. I'm guessing that it's a limitation.

[parisse]

If you don't find information in HP documentation, you should have a look at Xcas: area currently supports circles and polygons. There is no special object for conics, they are stored as parametric curves in the CAS (Geometry uses CAS objects).
I can extend the area command to parametric curves (including ellipses but also function and polar plots) using Green-Riemann theorem, but for non closed curves you will be surprised by the sign. Indeed I must close the curve to apply Green-Riemann, it's natural to close it with vertical segments at the boundaries and the Ox axis, but then you will not follow the curve in the trigonometric way : I will in fact compute int(-y*dx) along the curve. Note also that the area will be computed in approx mode (because the plotting functions do numeric evaluation of the boundaries).

[math7]

Parisse....

Have you ever added this functionality or have you not been present in the new update?

[parisse]

It's not implemented.