[mapserver-users] How to Optimize Particular Raster Lookup

[Pavel Iacovlev]

I would make something among this lines like cache all elevation for
each geometry.

1. Create a table elevation_points
id - (index)
table - table name (index) (if you have multiple data tables)
parent_id - id of the linestring (index)
the_geom - point - (index)
value - elevation value

2.
Make a PHP script that populates elevation_pointst table using the
algorithm you already developed, or create a ON UPDATE trigger for the
geometry, so then the geometry is changed the elevation_points are set
accordingly to changes.

3.
Using a SQL JOIN fetch the data in a preferred way very fast.

On Wed, Aug 12, 2009 at 5:40 PM, Blake Crosby<me at blakecrosby.com> wrote:
> Hello! Wondering if a few of you can provide some insight here:
>
> Problem: Given a linestring, return the elevation data along that
> linestring from CDED data (ASCII DEM).
>
> I'm using Mapserver 5.4.2
>
> I'm using PHP Mapscript and queryByPoint to get values from my DEMs.
> However, the performance seems really slow. Essentially here is how I
> have things set up:
>
> Fetch Linestring from postgis, and select N points from the string every
> Y distance (ie, get the points every 1 km).
>
> Loop through each point and do a queryByPoint() to get the value from
> Mapserver.
>
> I've tried using a tilecache, yo no avail. It still takes over 60
> seconds to query approx 200 points.
>
> I would like to use the 50k CDED dems, however the performance is even
> worse. So i'm using the 250k ones, approx 4,280 files.
>
> Any tips on improving performance?
>
> Blake
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