[Mapserver-users] PostGIS / Shapefile Performance Question

[Thomas, Cord]

Paul

This is what i understood ArcView (and mapobjects, and ArcInfo to be sure)
to do.

So, does MapServer read the sbn/sbx files?  or just the .shx file.  Oh wait,
sorry - wasnt paying attention - MapServer creates its own index, right?
So, was shpindex written to provide the quadtree index because the sbn
format is an unknown (according to
http://gdal.velocet.ca/projects/shapelib/shapelib.html it is unpublished) or
because the quadtree was proven to be better.

Has anyone ever been able to explore either with ESRI or others why the
sbn/sbx is undocumented?

Cord

-----Original Message-----
From: Paul Ramsey [mailto:pramsey at refractions.net]
Sent: Wednesday, January 15, 2003 11:29 AM
To: Thomas, Cord; mapserver-users at lists.gis.umn.edu
Subject: Re: [Mapserver-users] PostGIS / Shapefile Performance Question


Thomas,

Alot of confusion is caused by the fact that the SHX file is called the 
"index file". It *is* an index, but it is not a *spatial* index. It is 
an index of the byte offset location of shape records in the SHP file, 
which allows software to quickly read individual records out of the SHP 
file without scanning every single byte.

I was *wrong* about ESRI not providing spatial indexes on shape files, 
by the way. A quick read of the ArcView help file tells me that 
mysterious SBN and SBX files ArcView generates are some form of spatial 
index. Whether quads or grids or whatnot is not indicated. So if you 
want to ship your shape files around with indexes remember to generate 
and keep your SBN and SBX files.

P.

Thomas, Cord wrote:
> 
> could someone simply explain the difference between an "index of
> shapes" as provided by ArcView indexing of the shape field (i assume
> this is what you all mean) and a spatial index (which i understand to
> be some sort of fixed or flexible grid structure grouping sets of
> shapes into the grids).

-- 
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      | Paul Ramsey
      | Refractions Research
      | Email: pramsey at refractions.net
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