Geographic Information Systems Stack Exchange is a question and answer site for cartographers, geographers and GIS professionals. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

My question is quite clear:

Assume that there is an ellipse, namely EL1. Parameters of the ellipsoid are (focus11 [latitude, longitude], focus12[latitude, longitude], radius1).

And a second ellipse, namely EL2. Which is defined with the same parameter set (focus21 [latitude, longitude], focus22[latitude, longitude], radius2).

The reference ellipsoid is WGS84.

What is the method to find if EL1 contains EL2 ?

So far the best approach I come up with is to convert the EL1 and EL2 to polygons. But it is quite costly.

Is there any idea? Any help is appriciated. Waiting for your replys ...

share|improve this question
I think your parameters for EL1 and EL2 are incomplete. Two foci and a radius don't seem to be enough information to determine and ellipse. Somebody correct me if I'm wrong. – R.K. Dec 25 '12 at 13:03
@r.k. The two focii & radius implicitly give the semi-major & semi-minor axis. Hence the ellipse is fully defined. – Devdatta Tengshe Dec 25 '12 at 13:15
@OP Are you assuming the ellipse is on a flat surface, or is the earth's curveture important in your calculations? – Devdatta Tengshe Dec 25 '12 at 13:18
@DevdattaTengshe I'm a bit confused as to where the radius would be centered at. The foci? If so, aren't two focal radii(with different values) needed? An illustration would be most helpful I think. I hope the OP will reply soon. – R.K. Dec 25 '12 at 13:43
@R.K. Look at this:… If you have F1 & F2, and radius (I guess that means a) you can get the center(which is inbetween F1 & F2), and then you can calculate e, and then get the semi-minor axis – Devdatta Tengshe Dec 25 '12 at 15:41

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.