[gdal-dev] Fast Pixel Access

[Norman Vine]

This is an application that is just screaming for a spatial index

For starters you could build a spatialite db of the individual file extents
that returned the filename to pass to gdallocationinfo

On Feb 1, 2014, at 9:14 AM, "David Baker (Geoscience)" <david.m.baker at chk.com> wrote:

> Jukka,
> 
> Jukka wrote:
>> I was experimenting with something like a "GIS service without a GIS server)
>> and I have some examples online but...
> 
> I am looking to do as you have, a RESTful service to query the elevation at a given location.  This will be used to in a DQM process as well as a geologic application that needs the elevation of a proposed wellsite for data mining.  In both cases, 1000's if not tens of 1000's of calls will be made so performance is an issue.
> 
> David
> 
> 
> -----Original Message-----
> From: gdal-dev-bounces at lists.osgeo.org [mailto:gdal-dev-bounces at lists.osgeo.org] On Behalf Of Jukka Rahkonen
> Sent: Saturday, February 01, 2014 7:09 AM
> To: gdal-dev at lists.osgeo.org
> Subject: Re: [gdal-dev] Fast Pixel Access
> 
> David Baker (Geoscience <david.m.baker <at> chk.com> writes:
> 
>> 
>> 
>> 
>> 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? 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.
> 
> I was experimenting with something like a "GIS service without a GIS server)
> and I have some examples online but because of http connection the speed
> comparison does not make sense.
> 
> Vrt combining biomass data from 13 single band tif files
> gdallocationinfo
> /vsicurl/http://latuviitta.kapsi.fi/data/metla/puuston_tilavuus.vrt -geoloc
> 389559 6677412
> 
> DEM of Finland with 10x10 m grid through vrt
> gdallocationinfo /vsicurl/http://latuviitta.kapsi.fi/data/dem10m/dem_10m.vrt
> -geoloc  389559 6677412
> 
> The same from a single BigTIFF
> gdallocationinfo /vsicurl/http://latuviitta.kapsi.fi/data/dem10m/dem_10m.tif
> -geoloc  389559 6677412
> 
> Feel free to download the originals if you want, they are all made from open
> data. Just mention the National Land Survey of Finland, 2013 for the DEM and
> Finnish Forest Reserch Institute, 2013 for the biomass data if you publish
> data somewhere. The DEM datasets are about 10 GB each (Bigtiff + the
> original small ones).
> 
> My tiffs have tiles but for this usage where only the value of a single
> pixel is interesting striped tiffs could be as fast to read than tiled
> tiffs. A trial would tell everything
> 
> -Jukka Rahkonen-
> 
> 
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