[gdal-dev] Fast Pixel Access

[Brian Case]

evenr


what about the use of a tileindex? seems an intersection with a set of
polys first would be quick

brian





On Fri, 2014-01-31 at 19:30 +0100, Even Rouault wrote:
> Le vendredi 31 janvier 2014 17:15:53, David Baker (Geoscience) a écrit :
> > Dev's,
> > 
> > I have a set of 55,501 bil files in a single directory.  They are DEMS data
> > that cover the US in 7.5 minute tiles.  I would like to randomly access
> > elevations at a given lat/lon's from the whole dataset.  I created a vrt
> > file from the directory of bil files, and have been able to access the
> > elevation at a given lat/lon using gdallocationinfo, but because of the
> > size of the dataset, this operation is somewhat slow.  Can the vrt be
> > indexed?
> 
> No, it isn't currently, although I think it could be improved to have a in-
> memory index with moderate effort.
> 
> But are you sure the slowness is due to the lack of index ? 55,000 is a big 
> number, but not that big. Maybe the slowness just comes from the opening time 
> (XML parsing) of such a big VRT. That would need to be profiled to be sure 
> where the bottleneck is.
> 
> > Or, is there a faster, better way to access the pixels?  I would
> > first like to do this with the utilities before diving into code (C#). 
> > The files are regularly named base on their location within a 1 arc-second
> > grid.
> > 
> > Thanks,
> > David
> > 
> > David M. Baker
> > Senior Advisor - Geoscience Technology
> > Chesapeake Energy Corporation
> > david.m.baker at chk.com<mailto:david.m.baker at chk.com>
> > 
> > 
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