[Geojson] Geojson Digest, Vol 39, Issue 8

[Dale Lutz]

Hi,

With respect to circles and ellipses, I'd strongly suggest that the units
concept for the radii NOT be part of the spec. The units should be in the
units of the CRS, the same units as the X and Y are. Yes, for degrees it
is whacky, but I've yet to run into a GIS or spatial database system that
has allowed for different units of measure for the radii than the
coordinates.  If there is no CRS, then I still say the radii are assumed
to be measured in the units of the coordinates, I don't think there is
much gain in assigning an explicit unit in that case anyway and just adds
complexity.

For the rotations, specifying them in degrees is fine but be very very
clear that it is degrees counterclockwise from horizontal (if that is what
is decided, but hey, the CAD systems have done this), and not radians --
many's a customer of ours that has had radian/degree confusion over the
years, and lets not get started about clockwise or counterclockwise...

Dale
_____________________________________________________________________
Dale Lutz | Vice President Development
Safe Software Inc.
Suite 2017, 7445 - 132nd Street, Surrey, BC Canada V3W 1J8
T 604.501.9985 | F 604.501.9965
dale.lutz at safe.com | Twitter @DaleAtSafe | www.safe.com
_____________________________________________________________________

> Circles and Ellipses:
> https://github.com/GeoJSONWG/geojson-
> spec/wiki/wiki/Proposal%20Circles%20and%20Ellipses%20Geoms
>
> Let's be clear whether we're specifying paths or patches. Center
> coordinates + radius feels natural to me. If a CRS is defined,
> wouldn't it be best to apply those units to the radius? Otherwise,
> could we require units to always (MUST) be meters?
>
> An ellipse is complicated by the two axes and their orientation.
> Defining these differently than GML does would need a strong argument.
>
> Circles and ellipses can be approximated by polygons, but it becomes
> onerous for good approximations. I'm in favor of this proposal.
>