Wow. What version of PostGIS are you running?
Great to hear that the out-db works for you. I always expected that
out-db would work better for rasters with large numbers of bands.
out-db rasters does have the limitation that they are read-only.
-bborie
On 10/29/2012 05:02 PM, James Hiebert wrote:
>> I believe ST_Intersects() works on out-of-db rasters in the 2.0 series,
>> possibly 2.0.1.
>
> Hmmm, for me it it fails for the (raster, integer, geometry) signature:
>
> raster_test=> SELECT rid FROM basins INNER JOIN bcsd ON ST_Intersects(rast,
> 1, the_geom) WHERE rid = 39;
> ERROR: rt_raster_intersects not implemented yet for OFFDB bands
> CONTEXT: PL/pgSQL function "_st_intersects" line 20 at RETURN
>
> but it appears that you're right for the (geometry, raster, integer)
> signature:
>
> raster_test=> SELECT rid FROM basins INNER JOIN bcsd ON
> ST_Intersects(the_geom, rast, 1) WHERE rid = 39;
> rid
> -----
> 39
> (1 row)
>
>> I wonder what your benchmark's performance would be like if the raster
>> is out-db. I'd expect a flat line with little change regardless the #
>> of bands.
>
> Ah ha! Yes, that's definitely the case. With out of db storage, each of
> intersects/clip queries comes back in < 200ms, regardless of num bands.
> That's more of the behaviour that I was expecting, too. Thanks for helping
> me put a finger on it!
>
> ~James
>
> On Mon, Oct 29, 2012 at 04:33:36PM -0700, Bborie Park wrote:
>> I believe ST_Intersects() works on out-of-db rasters in the 2.0 series,
>> possibly 2.0.1.
>>
>> As for performance of in-db vs out-db, in-db is slightly faster but my
>> benchmarks are rather old. I hope to do some testing soon to see if I
>> can improve out-db performance.
>>
>> Tile size is critical regardless of whether or not you're going to store
>> your rasters in-db or out-db. Generally, tiles should be 100x100 or
>> smaller. Ideal tile size depends upon the input raster's dimensions and
>> what tile dimension is cleanly divisible from the raster's dimension.
>>
>> I wonder what your benchmark's performance would be like if the raster
>> is out-db. I'd expect a flat line with little change regardless the #
>> of bands.
>>
>> -bborie
>>
>> On 10/29/2012 04:23 PM, James Hiebert wrote:
>>>> If you've got a large number of bands (100s or more), you may want to
>>>> consider having the rasters be out-of-db.
>>>
>>> I had considered that (better, actually, than duplicating our data,
>>> right?), but was finding that st_intersects wasn't yet implemented for out
>>> of db storage. Looking through the trunk code, though, it appears that
>>> maybe you've gone ahead and implemented that since 2.0.1? If so, great!
>>> ST_PixelAsPoints() is another good reason for me to seriously consider
>>> working out of trunk...
>>>
>>>> Part of the problem is that
>>>> anything stored in PostgreSQL (in-db) is TOASTed so needs to be
>>>> deserialized (and probably decompressed). So, if the serialized raster
>>>> is big (more bands), the deTOASTing will take longer.
>>>
>>> Thanks; good to know.
>>>
>>>> Another problem with your benchmark query is that the ST_Clip() is
>>>> running twice (for height and width).
>>>
>>> Ah, that changes the picture pretty dramatically (see attached plot).
>>> Since it improves by a lot more than a factor of two, I suspect maybe I'm
>>> having some desktop scaling issues or something. I'll go ahead and
>>> actually put this on our database server, try the trunk version, and go
>>> from there. This is at least somewhat encouraging :) Thanks for the
>>> suggestions.
>>>
>>> ~James
>>>
>>> On Mon, Oct 29, 2012 at 03:50:04PM -0700, Bborie Park wrote:
>>>> James,
>>>>
>>>> I use PostGIS raster for a similar purpose (model outputs) though my
>>>> model outputs are for a specific day (average temperature for a specific
>>>> date). So, one raster with one band per day per variable. I could
>>>> combine a year's worth of bands into one raster but I decided against that.
>>>>
>>>> If you've got a large number of bands (100s or more), you may want to
>>>> consider having the rasters be out-of-db. Part of the problem is that
>>>> anything stored in PostgreSQL (in-db) is TOASTed so needs to be
>>>> deserialized (and probably decompressed). So, if the serialized raster
>>>> is big (more bands), the deTOASTing will take longer.
>>>>
>>>> Another problem with your benchmark query is that the ST_Clip() is
>>>> running twice (for height and width).
>>>>
>>>> If you're in the evaluation stage and you're compiling PostGIS yourself,
>>>> I'd recommend trying SVN -trunk (will become 2.1) as it has additional
>>>> capabilities and performance improvements. I'm already using -trunk in
>>>> production as I needed the new features (full disclosure: I wrote almost
>>>> the new features in -trunk).
>>>>
>>>> -bborie
>>>>
>>>> On 10/29/2012 03:32 PM, James Hiebert wrote:
>>>>> Hi All,
>>>>>
>>>>> I'm considering using PostGIS rasters for storage of raster data at my
>>>>> organization and I'm looking for some advice (or perhaps a reality
>>>>> check). I work for a region climate services provider and the vast
>>>>> majority of our data (by volume, not necessarily complexity) are output
>>>>> from climate models. These are generally a n-by-m raster with one band
>>>>> for each timestep. There could be upwards of 36k to 72k timesteps for a
>>>>> typical model run. We have hundreds of model runs.
>>>>>
>>>>> So my question is, is it insane to be thinking of storing that many bands
>>>>> in a PostGIS raster? Or more specifically, is this _not_ a use case for
>>>>> which PostGIS rasters were designed? I notice that most of the examples
>>>>> in the docs and in "PostGIS In Action" focus only on images and I can
>>>>> imagine that handling multispectral satellite images as being more of the
>>>>> intended use case.
>>>>>
>>>>> I did a little benchmarking of a typical use case of ours ("What's the
>>>>> average temperature inside a some polygon, e.g. a river basin?"). I
>>>>> noticed that the run time for doing a ST_Clip(raster, band, geometry) and
>>>>> ST_Intersects(raster, band, geometry) appears to be super-linear even
>>>>> when doing it on just a single band. I ran the following query:
>>>>> SELECT rid, st_height(st_clip(rast, 1, the_geom)), st_width(st_clip(rast,
>>>>> the_geom)) FROM basins INNER JOIN bcsd ON ST_Intersects(rast, 1,
>>>>> the_geom) WHERE rid = <rid> (where basins is table of river basins with
>>>>> one single polygon and bcsd is a table with a raster column "rast").
>>>>> for a set of rasters with increasing number of bands, and the time to run
>>>>> the query is shown in the attached plot. Since the raster properties are
>>>>> presumably shared across all the bands, it seems odd to me that run time
>>>>> would increase. I would expect it to be _contant_ (with constant number
>>>>> of pixels), but I suppose that that's my own ignorance as to how the PG
>>>>> type extensions work?
>>>>>
>>>>> Comments or explanations are welcome.
>>>>>
>>>>> ~James
>
--
Bborie Park
Programmer
Center for Vectorborne Diseases
UC Davis
530-752-8380
bkp...@ucdavis.edu
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