[Qgis-user] Which android tablet

[Tim Sutton]

Hi

On Thu, Jul 12, 2012 at 12:01 PM, Bernhard Ströbl
<bernhard.stroebl at jena.de> wrote:
>
>
> Am 12.07.2012 11:48, schrieb watercress at gmx.de:
>
>> Hi,
>>
>> has anyone tested the performance of qgis on android.
>>
>> I want to collect and store the position of 50 trouts tagged with radio
>> transmitters directly in the field.
>>
>>
>> What I did so far:
>> I have to aim at the targets from different locations at the river bank.
>> What I do now is simply draw lines on printed orthophotos. The fish is
>> located where the lines intersect. It is always quite a mess to
>> determine your own position. I could save the origin with a gps-device
>> but this takes too much time, would include "postprocessing" and adding
>> another step will increase the source of error.
>>
>> ... and it is not possible to walk into the stream ...
>>
>>
>> I am thinking of using a tablet, locally store the orthophotos (5 to 8
>> pieces, format: .jp2, each around 130 MB) and save the points (e.g.
>> postgis). All metadata could be entered at once. No paper work. I know
>> where I am and can easily store, edit,.. fish data in the field.
>>
>> But I am bit worried about the performance. I takes about two til four
>> minutes to load those raster-layers at my desktop (Ubuntu 12.04, 16GB
>> Ram, QuadCore,...). The performance appears very poor.
>
>
> This is weird. I am not a specialist with raster formats but one of my
> aerial photos (geotif) 281 MB loads and displays within seconds, this is
> with pyramids (maybe you need to build these?)
> I even put some 50 of these photos into a GDAL virtual raster (VRT), it
> takes some 20 seconds to load but displays almost immediately.
> My machine is similar to yours hardwarewise (less RAM, though) running
> OpenSUSE 64 bit.
>

I think the jp2 drivers are quite slow. A nice solution is to load
your rasters into an mbtiles sqlite database - its not the best for
size, but its very good for performance.

Note it needs a recent (unreleased?) version of GDAL.. Otherwise
convert your data to tiffs as Bernhard has done and optimise them for
performace by e.g. creating pyramids.

Regards

Tim

> Bernhard
>
>
>>
>> What can I expect from a tablet solution? Anything missing in my chain
>> of thoughts?
>>
>> I really appreciate any hints, ideas ,..I also would like to contribute
>> my experience as a case study for the qgis-website.
>>
>> Regards,
>> Jens
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>>
>
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Tim Sutton - QGIS Project Steering Committee Member (Release  Manager)
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