Polygon CCW winding check request

[Marco Molinaro]

Dear DAL members,
at the recent IVOA Interop in Victoria it was pointed out
by Alberto

http://wiki.ivoa.net/internal/IVOA/InterOpMayy2018DAL/ivoa_
201805_micol_polygons.pdf

that not all the data providers follow the STC specification
about the winding direction of polygons stored in their
archives.

STC states that "The inside of the region is defined as
that part of coordinate space that is encircled by the
polygon in a counter-clockwise sense".
And this is to be considered when looking at the
celestial sphere from the inside.

The different behaviour of the polygons stored at
different sites creates an interoperability issue.

This email is a request on data providers to check
on their data and implementations (when dealing
with polygons) to solve the presented issue.

James also put together a python code snippet
implementing a simple test, it is available here:

https://gist.github.com/jd-au/45d1cdc0c6e2a7bc848a4be8f46c8958

Thank you in advance!
Cheers,
       Marco & James
      (your DAL chair & vice)
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.ivoa.net/pipermail/dal/attachments/20180612/a810959e/attachment.html>