[OSGeo-Discuss] multipatch shapefile FIRST_RING structure

Rushforth, Peter Peter.Rushforth at NRCan-RNCan.gc.ca
Mon Jan 26 10:10:24 PST 2009


I posted the following question here:
but got no response.

Maybe the community will come to the rescue.

The shapefile spec for multipatch shapefiles says this: 

"When the individual types of rings in a collection of rings representing a polygonal patch with holes is unknown, the sequence must start with First Ring, followed by a number of Rings" (p 21). 

Figure 3 shows a "First Ring" as an inner ring with an exterior ring as a "Ring". 

Does this mean a receiving application must be prepared to figure out the (3 dimensional) topology of the rings it reads from a shapefile? Why? When would this ever be the case? I mean an application that doesn't know which is the exterior ring from the interior rings of an internal data structure has no business writing them out and thus make them someone else's problem, in my view.

Thanks for your insights,

Peter Rushforth
Technology Advisor / Conseiller technique
GeoConnections / GĂ©oConnexions
650-615 Booth St. / rue Booth
Ottawa ON K1A 0E9
E-mail / Courriel: Peter.Rushforth at NRCan-RNCan.gc.ca 
Phone / TĂ©lephone: (613) 943-0784 
Fax / telecopier:  (613) 947-2410

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