[mapguide][MG411][Modified] Allow negative buffer offsets

[Walt Welton-Lair]

You can view the artifact detail at the following URL:

    https://mapguide.osgeo.org/servlets/Scarab/id/MG411

Type:
Enhancement

Artifact ID:
MG411 (Allow negative buffer offsets)

Modified by:
Walt Welton-Lair
waltweltonlair (walt.welton-lair at autodesk.com)

The following modifications were made to this artifact:
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-- Resolution set to new value:
Submitted
-- Developer Notes set to new value:
* Updated the public API to allow negative buffer offsets.  Note that negative offsets only make sense for polygons.

* Implementation of this for polygons is actually straightforward.  In the normal case (positive offset) we create the buffer using PolygonBuffer::CreateBufferZone.  This generates a buffer on either side of the polygon boundary, and the inner buffer is eventually discarded.  For the negative offset case, we use a new class called PolygonSetback which inherits from PolygonBuffer.  Both sides of the polygon are again buffered, but we override the AcceptBoundary method so that now the outer buffer gets discarded.

* The m_hookEdgeLength variable was not getting properly initialized in BufferUtility.  Fixed this.

* Added a ReverseBoundaries method to OrientedPolyPolygon.  The polygons created by the setback code have the reverse orientation (CW), and they need to be changed back to CCW before creating an OrientedPolyPolygonUnion.




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