confusion about polygon definitions

[Stephen Woodbridge]

Joe,

mapserver assumes an XY coordinate system there for there is only ONE
polygon the mapserver will understand and the is P2 below. P! is really
two separate polygons and should be split into them respectively. You
can define a polygon that crosses the international date line by add/sub
180 to the values beyond the dateline, but these will not get wrapped to
the opposite side of the image.

In summary mapserver does not understand the topology of a sphere on the
infinite expanse of X and Y cartesian coordinates.

-Steve W.

Joseph Bussell wrote:

> How does one differentiate the polygon:
>
>    P1:  (  10,   179 )  (  -10,   179 )  (  -10,  -179 ) ( 10,  -179 ),
>    interior point at ( 1,  179.5 )
>
> from
>
>    P2:  (  10,   179 )  (  -10,   179 )  (  -10,  -179 ) ( 10,  -179 ),
>    interior point at ( 1, 100 )
>
> P1 is a small square at the international dateline.
> P2 is the large strip that wraps around the globe.
>
> My goal is to display both as unique.  I have several polygons which
> straddle the dateline and are not filling correctly.  I note however
> that the Asia polygon in my world shapefile crosses the dateline just
> fine.  Siberia appears correctly divided as one would expect.  Is there
> a point order such as a couter-clockwise point addition?
>
> Cordially,
>
> Joe Bussell
> On Time Systems
>