[Gdal-dev] Any hints on increasing performance?

[Frank Warmerdam]

Rick Niles wrote:
> I've written a program to show line-of-sight coverage of various radars 
> and aircraft navigation aids such as DME and VOR.  It should also work 
> for com links as well.  I used the GDal library for reading in the 
> terrain data (DTED Level 1, USGS DEM, or GTOPO30).  The problem is 
> performance.  To do all of 48-US states it takes about an hour, which 
> may seem quick, but I wanted to make it a web based application that has 
> a faster turn-around.
> 
> I'm calling GDALRasterIO for one point at a time.  I know that's what 
> everyone is going to say that is the bottleneck, but I tried reading all 
> the data into arrays and it took 100x longer, because I don't use a 
> large chunk of the data and reading it all in was quite time consuming, 
> not to mention it used a huge amout of memory.   Also, with the caching 
> that GDAL does, it works quite well.  BTW, I coverted the DEM and 
> GTOPO30 data in GeoTiff format which helped a whole bunch too.

Rick,

Can you explain a bit more about what pixels you do need?  Is it always
a particular subset?  If you only need a subset of the data, then you need
to organize your data to support the access strategy.  To help you we will
need to know more about your access strategy.

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