Contours again.

[Frank Warmerdam]

Ed McNierney wrote:
> Bob -
>
> If things got 25% faster, the index is being used - you don't need to do anything other than create it.  Do you have a feel for what level of bandwidth you're getting from the NAS server?  Roughly what percentage of the vectors in the shapefile are being used to draw your test image?
>
> Don't mess around with different values yet - just use the default.  It sounds like you're suffering from either excessively-detailed data (needs simplification for the scales you're using), a test that draws a large percentage of the vectors in the file, and/or poor throughput to the file server.  A simple test would be to copy the shapefile to the local disk just to see if there's a difference.


Guys,

I haven't followed this discussion very closely, so I may have missed
something.  But one issue I have encountered with contours is that they
often end up being very large polygons.  For instance, a "zero elevation"
coastal contour might well be continental sized.  Really big "rings" get
pushed way up the the spatial index tree and will have to be read from
disk and rendered even if the current map view is just somewhere inside
the contour ring such that the contour won't actually be visible, but
the bounding rectangles of the contour and the view area will overlap.

If this is Bob's problem, he will really be much better off to split the
contours into shortish line segments instead of keeping as massive single
geometries as this would allow the spatial index to localize things
much better.

I didn't speak up about this before because it wasn't clear if this has
already been done.

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