I have a very basic question about the OGC SFA model. My apologies if this is
the wrong forum to discuss this question, (any suggestions for alternatives?).
Suppose you have a POLYGON that straddles the +/- 180 degree longitude. From my
reading of the SFA spec, line segments are contained within the plane and there
is no concept of wraparound. So I would represent this polygon as a
MultiPolygon with two components, splitting the polygon at 180.
Most operations on such a polygon should work correctly, but I think there at
least a couple of problems. One possible problem is that NumGeometries()
function is arguably wrong. I have a single polygon (the abstract one that
wraps around 180), but I was forced to split it into two pieces. Also,
Envelope() seems wrong. The definition of this function says:
The minimum bounding box for this Geometry, returned as a Geometry. The polygon
is defined by the corner points of the bounding box [(MINX, MINY), (MAXX,
MINY), (MAXX, MAXY), (MINX, MAXY), (MINX, MINY)]. ... The simplest
representation of an Envelope is as two direct positions, one containing all
the minimums, and another all the maximums. In some cases, this coordinate will
be outside the range of validity for the Spatial Reference System.
Ideally (I think) the Envelope() would also straddle 180. However, this won't
happen, given the dependence on MINX and MAXX, and it is even possible that the
polygon and its Envelope() would be disjoint!
I’d appreciate any thoughts on how to represent objects that straddle 180. Am I
barking up the wrong tree?
Jack Orenstein
------------------------------------------------------------------------------
Want fast and easy access to all the code in your enterprise? Index and
search up to 200,000 lines of code with a free copy of Black Duck
Code Sight - the same software that powers the world's largest code
search on Ohloh, the Black Duck Open Hub! Try it now.
http://p.sf.net/sfu/bds
_______________________________________________
GeoTools-GT2-Users mailing list
GeoTools-GT2-Users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users
