[fdo-internals] FDO RFC 48 - Polygon Vertex Order is ready for review.

[Traian Stanev]

Hi

I have some concerns with the class capabilities part of the RFC.

The class capabilities will introduce the vertex order hint and the strictness setting. Introducing the vertex order hint will result in many existing SDF files (for example) having the "wrong" vertex order, since there are many SDF files which started life as SHP files.

The above means that having the vertex order hint is not useful for many SDF files (and also many SHP files written out by applications which don't enforce winding order, and also other formats), and the consuming application will have to fix the vertex order if it really cares. MapGuide for example does not care - it can render polygons with any winding you give it. So the vertex order hint seems like it will only add confusion. An application which does care will have to ignore the vertex order capability, since it is not really true (as described above). Hence the vertex order setting is not useful for both applications which do care about vertex order and for applications which don't care about it.

The strictness hint is also problematic. Most providers will use the "not enforced" setting, which means that you can still store any kind of polygon in them. In fact only one data source (and not in all cases) requires strict vertex order - SQL Server. All other cases would mean per-provider coding of strictness enforcement in case we want "enforced" vertex order.

So, if the capability provides no correct information about vertex order and no meaningful enforcement of vertex order, is it needed at all?

Traian



From: fdo-internals-bounces at lists.osgeo.org [mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Leaf Li
Sent: Tuesday, July 06, 2010 6:15 AM
To: fdo-internals at lists.osgeo.org
Subject: [fdo-internals] FDO RFC 48 - Polygon Vertex Order is ready for review.

All,

FDO RFC 48 - Polygon Vertex Order is ready for review. Can you review it?
http://trac.osgeo.org/fdo/wiki/FDORfc48

Thanks,
Leaf Li
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