[Freegis-list] shapelib question

Adrian Custer acuster at nature.berkeley.edu
Fri Apr 6 18:43:36 CEST 2001

You might write the folks on the FMaps project (sourceforge). They have
spent the better part of the last years working to develop the
PostgreSQL geographic data types and should be able to help you.


On 06 Apr 2001 11:28:52 -0400, Timothy H. Keitt wrote:
> Frank Warmerdam wrote:
> > 
> > Multi-part polygons may be multiple islands (one feature, but disconnected
> > outer rings), or one polygon with holes (or a mixture).  In theory you
> > are supposed to be able to determine this from the winding direction of
> > the rings (whether they are outer or inner edges) but in practice many 
> > systems don't setup this distinction up properly (like most applications
> > using Shapelib to write) so you pretty much have to determine yourself. 
> > 
> (O.K. basic geometry here, but bear with me.)  If turning right is negative
> and turning left is positive, then if the sum of turning angles is negative,
> the winding direction is clockwise, no?  Is there a convention that inner
> edges are digitized in a particular direction?
> My dilema is whether to use an array of polygons in postgresql, or to use a
> seperate table with multiple entries corresponding to a given "shape."  I don't
> know if postgesql polygons can contain (or understand) holes or not.
> Tim
> -- 
> Timothy H. Keitt
> Department of Ecology and Evolution
> State University of New York at Stony Brook
> Phone: 631-632-1101, FAX: 631-632-7626
> http://life.bio.sunysb.edu/ee/keitt/
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