[postgis-users] design comments

Theller, Lawrence O. theller at purdue.edu
Wed Feb 11 14:17:14 PST 2009

HI from excited new user; the raster discussion really piques my
interest. Would welcome some design comments.
We now have an online model that reads large collection (1 TB) of raster
files, queries an oracle DB (tabular not spatial) does some
manipulations and presents results with Mapserver.  User interface
starts and stops with Mapserver with display of 5 states worth of GIS
files I manage; like to get out of that business by going to Google
I have designed a  grand replacement strategy from reading web pages and
I now realize perhaps I need some feedback from experienced users. My
hope is to convert the raster files into xyz point data stored in
postgresql - stored in large watershed subsets of a state as a table of
points indexed by small watersheds among other things, with 5 to 10
attributes per point. A typical (8 digit watershed) table then would be
maybe 52 million points with 15 attributes.  A state would have dozens
of this size table. We would present the user with Google Maps
interface, they draw a box which passes to us, we do spatial query to
find which watershed they are in and read and spatial query the
appropriate table of points with attributes,  and manipulate. 
I hope this is faster than current method which is to find appropriate 5
physical raster files, 50 Megabytes each, say; read them into memory and
then query out appropriate subarea and manipulate, results now include
create both ascii raster and xy generate file, and then a shapefile This
output process I would replace with just KML output (points with changed
attributes get output)
 So the real question is will the database efficiently handle spatial
query into 52 million well-indexed points, or should I stick with
reading raster layer upon layer? BTW these are categorical and not image
rasters, for example soil type and landcover type with derivatives. Not
.tifs either at this point, we use a homebrew binary we make from ESRI
raster. Query will be a (KML/GML) polygon generally.
Any thoughts are welcome.
Larry Theller
Ag and Bio Engineering 
Purdue University
LTHIA model: http://cobweb.ecn.purdue.edu/~watergen/owls/htmls/reg5.htm
select a state
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