[postgis-users] Summarystats (Raster, Polygon)

[Duncan Golicher]

Can I ask Pierre his opinion on applying nearest neighbour resampling
within a query in order to speed things up when precision is not the
top priority, but many polygons or buffers have to be used?

Would this work, and if so what would the query look like?

Duncan


On Fri, Nov 16, 2012 at 10:09 AM, Duncan Golicher <dgolicher at gmail.com> wrote:
> Hello Andreas,
>
> Comparisons with Arc are always interesting to have.
>
> Can I ask how the speed of running the queries compares? We have been
> implementing some similar queries but found them to run rather more
> slowly than would be ideal. Pierre has suggested that this is due to
> using the pgsql version of st_clip rather than the new C version, but
> I have not yet managed to update to that as it does not seem to be
> part of the nightly build yet.
>
> I have also found these sort of queries to be VERY sensitive to tile
> size, with speed optimising at a mid range size making it quite tricky
> to find the best tile size, especially as it will also depend on the
> size of the polygons that are being used.  It would be interesting to
> know what your experience has been.
>
> Duncan
>
> On Fri, Nov 16, 2012 at 5:41 AM, Andreas Forø Tollefsen
> <andreasft at gmail.com> wrote:
>> Hi Pierre and thanks for your reply.
>>
>> My nodata values are well defined and are excluded in the summarystats
>> operation.
>> I also tried inverting the order of (geom, rast) without this changing the
>> results.
>>
>> Could this be explained by the possibility that Postgis and ArcGIS handels
>> pixels at the border of the polygon differently? i.e. that one includes
>> pixels intersecting, while the other only includes pixels if the centroid of
>> the pixel intersects?
>>
>> Andreas
>>
>>
>> 2012/11/15 Pierre Racine <Pierre.Racine at sbf.ulaval.ca>
>>>
>>> > Any suggestions why the results are not the same?
>>>
>>> Are your nodata values well defined?
>>>
>>> Might also be, depending on the version you have, the order in which you
>>> pass the geometry and the raster to the ST_Intersects() function. Try
>>> inverting them.
>>>
>>> > Any improvements to the query maybe?
>>>
>>> Not really.
>>>
>>> Pierre
>>>
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>>
>>
>>
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>
>
>
> --
> Dr Duncan Golicher
> Investigador Titular,
> El Colegio de la Frontera Sur, Chiapas,Mexico
> Mexico tel +52 1 967 137 94 20
> Skype name duncangolicher
>
> Publications: http://www.mendeley.com/profiles/duncan-golicher
>
> Senior lecturer, Bournemouth University, UK
> Centre for Conservation Ecology & Environmental Change
> School of Applied Sciences
> Christchurch House rm C218a
> Bournemouth University
> Fern Barrow
> Poole (Dorset) BH12 5BB UK
> Tel. +44 (0)1202 961682
>
> For list of publications see Researcher ID:
> http://www.researcherid.com/rid/B-4240-2009
>
> dgolicher at bournemouth.ac.uk
> dgoliche at ecosur.mx
>
> Researcher ID:
> http://www.researcherid.com/rid/B-4240-2009



-- 
Dr Duncan Golicher
Investigador Titular,
El Colegio de la Frontera Sur, Chiapas,Mexico
Mexico tel +52 1 967 137 94 20
Skype name duncangolicher

Publications: http://www.mendeley.com/profiles/duncan-golicher

Senior lecturer, Bournemouth University, UK
Centre for Conservation Ecology & Environmental Change
School of Applied Sciences
Christchurch House rm C218a
Bournemouth University
Fern Barrow
Poole (Dorset) BH12 5BB UK
Tel. +44 (0)1202 961682

For list of publications see Researcher ID:
http://www.researcherid.com/rid/B-4240-2009

dgolicher at bournemouth.ac.uk
dgoliche at ecosur.mx

Researcher ID:
http://www.researcherid.com/rid/B-4240-2009