[mapserver-users] How to Optimize Particular Raster Lookup

[Blake Crosby]

Pavel,

Thanks for the suggestion, but this wont help. The geometries aren't 
predetermined, but created on the fly by the user.

Blake

Pavel Iacovlev wrote:
> 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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>>
> 
> 
>