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Subject: RE: Polygon in TargetAreaType


What does ISO 19107 state for Exterior Ring Orientation for a polygon?  I haven’t had any problem accomplishing this in Where, because as you stated, it’s very clear how the points have to be arranged.  The problem here is that targetarea in the DE is just a string of points and I wasn’t sure if we need to specify ring orientation in the conformance document.



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From: Carl Reed [mailto:creed@opengeospatial.org]
Sent: Wednesday, May 05, 2010 10:01 AM
To: McGarry, Donald P.; emergency@lists.oasis-open.org
Subject: Re: Polygon in TargetAreaType


Rather then "invent" a specific approach for targetArea, why not follow ISO 19107 as the abstract model and GML as the "implementation" instance? Polygon is defined in the OASIS "where" draft and in the requirements document (which is available in the Kavi document archive). Very clearly stated. We should be consistent with how ISO, OMA, IETF, OGC, and others are defining polygon.





----- Original Message -----

Sent: Monday, May 03, 2010 9:41 AM

Subject: Polygon in TargetAreaType


Carl and others-


The Polygon element in targetArea is a list of lat lon pairs that represents a polygon.  However, one problem that I have noted when storing polygons in a geospatial database, or exposing to GIS tools is RingOrientation.  Notably, you normally follow the “left-hand” rule, which states that if you are walking the polygon you left hand should be pointing towards the center of the polygon area, which results in a counter-clockwise representation of points in the polygon.  If this is the case, I think our example in the DE documentation was constructed using the opposite linear ring orientation.  When validating a polygon, do we assume a certain ring orientation, or state that it can be either or, and just take the case that doesn’t span multiple hemispheres?


Don McGarry

The MITRE Corp.

Office: 315-838-2669

Cell: 315-383-1197



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