[Gdal-dev] RasterIO() speed

[Gerald Brandt]

Hi,

I have a loaded DEM file (USGSDEM/USGS Optional ASCII DEM) of Lake
Tahoe.  It's size is 3516 x 8430 x 1.

My command is 

dataset->GetRasterBand(1)->RasterIO(GF_Read, xpixel, yline, 1, 1,
&elevation, 1, 1, GDT_Float64, 0, 0) ;

With and xpixel value of 329 and a yline value of 4199.

The RasterIO() call takes 340 seconds on a Pentium 4 2.8 GHz
hyper-threaded system.  The cpu sits between 17% and 25% while in the
call.  Is this normal, and if so, is there a way that I can speed up the
process other than caching the elevation in my own array for every point
in the grid?

Thanks,

Gerald