[gdal-dev] Fast Pixel Access

[Joaquim Luis]

> Now what to do instead? A WMS/WCS service can send a piece of DEM with
> thousands of pixels as GeoTIFF in a second and a heavy client like QGIS
> could continue the analysis. Or you can use the existing vrt file and read
> the region of interest with gdal_translate. This request is not very fast
> either but it brings you one million height values faster than possible
> users could find the rope
> gdal_translate -of GTiff -srcwin 10000 10000 1000 1000
> /vsicurl/http://latuviitta.kapsi.fi/data/dem10m/dem_10m.vrt test_1000by1000.tif
>
> Or then WFS service could be used to send only thos DEM cells which
> intersect the requested point/line/area. That could be nice for further
> processing  but in that case your DEM should be converted into points or
> polygons. I wonder if PostGIS raster has something to give for you. Or
> perhaps there is some other clever way to do the job with light and powerful
> tools. Ideas are welcome.

Funny, I had tried this idea with GMT, but took an awful long time ~34 s 
while the gdallocationinfo approach took ~14 secs

echo 389559 6677412 | grdtrack 
-G/vsicurl/http://latuviitta.kapsi.fi/data/dem10m/dem_10m.vrt 
-R389000/390000/6677400/6678000

I have idea why through GMT it takes longer since it's still GDAL who 
gets the data from the remote location. And furthermore I require only a 
small grid chunk (the -R... limits)

Joaquim