[postgis-users] tile size

[Duncan Golicher]

Hi Bborie,

OK, I might well have been thinking on old lines. So I tested again against
the R extract function with the same data (this time on my slow laptop)

https://dl.dropboxusercontent.com/u/2703650/SpeedTestPointOverlay.html

You are quite right! With a tile size of 200 to 300 or so PostGIS now does
beat the extract function in the raster package (although still slower with
suboptimal tile sizes). This was certainly not the case when I tested a
year ago (when all runs were several orders of magnitude slower unless tile
size was  very small, in which case load time was prohibitive). ST_VALUE is
now performing very differently (postgis2.2dev  compiled from source). More
good news!

Duncan


On Thu, Sep 19, 2013 at 9:18 PM, Bborie Park <dustymugs at gmail.com> wrote:

>
> Note that the point on raster overlay can be beaten easily for speed by
>> the extract function in the R raster package. However the polygon overlays
>> are now very fast and compare well with any alternative way of getting the
>> result. Using PLR to run  R functions within PostGIS is great if you want
>> medians, quartiles etc or any other derived property.
>>
>>
> I wonder what is going on to make the point on raster overlay in PostGIS
> slower than in R. I'd have expected the numbers to be about the same as
> that operation is conceptually very simple.
>
> -bborie
>
>
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-- 
Dr Duncan Golicher
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Bournemouth University
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Researcher ID:
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