Hi Regina,
Actually it's more like I have 7 raster tables, one for each day, and i
would like to create a new raster as the average of those seven days.
AT this point I'm just trying to determine the structure and logic for
my db. Since rasters are new to me, I also have fundamental questions.
The data are always over the same domain, a number of daily weather
variables (temp, rainfall, humidity, etc). Is it best to break these
out by date and variable as I am now, with tables such as
"temp_12-22-2011", "temp_12-21-2011", "precip_12-22-2011",
"precip_12-21-2011", etc......or should I put all the vars for one date
in one table? In my my test db I have them by date, by variable, so the
query I want to try first is the one I mention above.
Thanks,
Steve
On 12/22/2011 2:44 PM, Paragon Corporation wrote:
Steve,
Depends how your data is setup -- I'm assuming you are looking for a moving
average?
If for example you have a raster record for each date in the same table,
with a field denoting the date, then the best bet is probably use ST_Union
with the optional MEAN expression.
I haven't stress tested that yet.
So say you have a table
Rast, temp_date
Then you can do a
SELECT ST_Union(rast, 'MEAN' ) OVER (ROWS BETWEEN 1 PRECEDING AND CURRENT
ROW ORDER BY temp_date) As newrast, temp_date
FROM temperatures;
Haven't tried using with window aggregates , but the above should work.
Also note the ROWS with number ranges was introduced in PostgreSQL 9.0 so
that particular syntax won't work with 8.4.
Hope that helps,
Regina
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Stephen
Crawford
Sent: Thursday, December 22, 2011 2:23 PM
To: PostGIS Users Discussion
Subject: [postgis-users] raster map algebra question(s)
Thanks to all who helped me on my previous raster output questions; I now
have a better handle on what I can (and can't) do.
How can I do map algebra across raster tables? I have a db of raster tables
(all the same extend) with weather variables by date. I have a number of
ways i want to use these data, but in the initial case I would like to, as
an example, create a new raster table where the data value at each cell is
the average of the previous day's values. Any thoughts?
Thanks,
Steve
--
Stephen Crawford
Center for Environmental Informatics
The Pennsylvania State University
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--
Stephen Crawford
Center for Environmental Informatics
The Pennsylvania State University
[email protected]
814.865.9905
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