Projection used to prepare SIGWX objects in WAFC SIGWX charts

[blchoy]

Referring #52.

Both ICAO Annex 3 and WAFCs' document Representing WAFC Significant Weather (SIGWX) data in BUFR do not give any clue whether metadata on projection is required for representing SIGWX objects for WAFC SIGWX charts as in VAA, SIGMET and AIRMET. In fact, the latter document suggests rendering software to use cubic spline routine for smoothing the line between points irrespective of the output projection. This seems to imply all SIGWX objects are prepared on the same projection or the difference between the projections for preparation and rendering are irrelevant/insignificant.

We may want to confirm with WAFCs on the need of projection metadata for SIGWX objects.

[blchoy]

This is closed as discussions and follow up actions would be handled in #54.