On Wed, 12 Feb 2014, Luis Sequeira wrote: > For the two radii, the polar coordinates are the good answer. Luis, Thank you very much. Rich -- Richard B. Shepard, Ph.D. | Have knowledge, will travel. Applied Ecosystem Services, Inc. | <http://www.appl-ecosys.com> Voice: 503-667-4517 Fax: 503-667-8863