[Gdal-dev] Any hints on increasing performance?

[Ed McNierney]

Rick -

Could you describe the process/algorithm a bit more?  How many points
are in your data set (that is, how many "radars and aircraft navigation
aids" are involved)?  How are you pruning the data for the curvature of
the Earth - i.e. what portion of the terrain data is used for each
point?

	- Ed

Ed McNierney
President and Chief Mapmaker
TopoZone.com
-----Original Message-----
From: Rick Niles [mailto:fniles at mitre.org] 
Sent: Wednesday, April 07, 2004 2:34 PM
To: gdal-dev at remotesensing.org
Subject: [Gdal-dev] Any hints on increasing performance?

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.

Anyway, the obvious answer is to just not evaluate as many locations,
but I just thought I'd ask if someone had a better solution, since that
effects the accuracy of the results.

I'm working on convincing my employeer to let me release it as 
open-source.   We'll see how that goes.

    Thanks,
    Rick Niles.


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