Thank you so much for your answer Shlomo, the Geodetic calculations with Porphyry intermediate cusps sound great, I think I might go with that
I'll send you my donation as soon as I get past my problem with the paypal page...

Love,
Dyane

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"It is only with the heart that one can see rightly; what is essential is invisible to the eye."
- Antoine de Saint-Exupéry