[mapserver-users] Polygon Questions

[Ed McNierney]

Frank -

I've done a moderate amount of shapefile generation/modification with
shapelib and used the results in MapServer.  I've found nothing that
contradicts your comments below about shapefiles.

	- Ed

Ed McNierney
Chief Mapmaker
TopoZone.com
ed at topozone.com
(978) 251-4242


-----Original Message-----
From: Frank Warmerdam [mailto:warmerdam at pobox.com]
Sent: Thursday, November 08, 2001 9:48 AM
To: Stephen Woodbridge
Cc: MapServer List
Subject: Re: [mapserver-users] Polygon Questions




Stephen Woodbridge wrote:

> Hi again,
> 
> Does mapserver, or shapefiles for that matter, care if polygon points
> are ordered clockwise or counter-clockwise?
> 
> In shapefiles, a polygon can be in multiple parts?
>   1) Does this mean multiple smaller closed polygons which constitue a

>      large object?
>   2) A large polygon, where the additional parts represent islands in
>      the larger one.
>   3) something else all together :)
> 
> -Stephen Woodbridge



Stephen,

o I don't think MapServer cares about the direction of polygon vertices.

o The Shapefile spec is specific about the ordering of vertices in the
   rings based on whether they are exterior or interior rings; however,
   it doesn't appear that ESRI products depend on this, and many
generators
   of shapefiles are careless in generation (notably my own Shapelib!).

o Shapefile polygons can be multiple islands as well as having holes in
   islands.  Both options are correctly handled by MapServer.


I could be wrong on any of the above, but I am pretty sure I am right.

Best regards,

-- 
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I set the clouds in motion - turn up   | Frank Warmerdam,
warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Programmer for Rent