>
>Agreed. The REGION construct, which takes a string representation as
>argument,
>is the general purpose method. POLYGON is limited to great circle edges.
>
>My thinking in writing that statement was to express that RECTANGLE is just
>a
>short-cut way to make a POLYGON; the edges are still great circles (and not
>lines of equal longitude or latitude). If you transform it, then it is still
>the same shape (POLYGON) but it probably cannot be written in "short-cut"
>form of RECTANGLE because there will no longer be just 2 longitude and 2
>latitude values. Since it brings very little real value when defined that
>way, it may be best to just remove it (Bob: that is something we discussed
>at
>one point).
>
Well, some explanations would be needed for the RECTANGLE construct: obviously it can generally NOT be built from great circles joining vertices having spherical coordinates (ra1, dec1) (ra1 dec2) (ra2 dec1) (ra2 dec2). The best way of clarifying this point would be, in my opinion, to write down the formulae giving the relations between the 4 coordinate numbers used in the RECTANGLE function, the coordinates of the vertices, and the center/width/height of the box. In particular, as already mentioned, if one of the dec's is +/-90degrees, no rectangular box can be defined.
For me, the most 'natural' way of specifying this rectangular box would be to give a center + width + height; giving 2 longitudes and 2 latitudes generally don't work.
--francois
Francois Ochsenbein ------ Observatoire Astronomique de Strasbourg 11, rue de l'Universite F-67000 STRASBOURG Phone: +33-(0)390 24 24 29 Email: francois-at-astro.u-strasbg.fr (France) Fax: +33-(0)390 24 24 32 ================================================================================Received on 2008-05-16Z01:59:13