Ok, looking for a SQL guru out there…
Want to see if something is even possible or not using GRASS (using 5.4)
Here is the situation… I have 2 files, once containing xyz pts, and another containing polygons. I am wondering if there is a way to use a sql query to find the average elevation for a given polygon?
I am trying right now to use MapInfo to do this query, but it doesn’t like the amount of points I am query (> 1,500,000) and knowing that GRASS is much better at processing and dealing with larger files, wondered if a query like this is possible…
Any ideas??
Thanks in advance!
Cheers!
Kevin Slover
Coastal / GIS Specialist
2872 Woodcock Blvd Suite 230
Atlanta GA 30341
(P) 678-530-0022
(F) 678-530-0044
Slover, Kevin wrote:
Ok, looking for a SQL guru out there…
Want to see if something is even possible or not using GRASS (using 5.4)
Here is the situation… I have 2 files, once containing xyz pts, and another containing polygons. I am wondering if there is a way to use a sql query to find the average elevation for a given polygon?
I am trying right now to use MapInfo to do this query, but it doesn’t like the amount of points I am query (> 1,500,000) and knowing that GRASS is much better at processing and dealing with larger files, wondered if a query like this is possible..
Any ideas??
If you really want to do this in SQL you could use PostGIS. I have done similar operations on tables with between a few hundred and >200,000,000 records, and have had no real problems. I have found that a monolithic spatial join as you require can be slow, but it can usually be broken down into separate queries, each dealing with a subset of the data, running sequentially via a script, and the reponse is orders of magnitude faster.
If this option is of interest, let me know & I can go through how I have done 9& optimised) such things...
Cheers
Brent Wood
Kevin,
On Thu, Jul 27, 2006 at 05:09:18PM -0400, Slover, Kevin wrote:
Ok, looking for a SQL guru out there...
Want to see if something is even possible or not using GRASS (using 5.4)
Here is the situation... I have 2 files, once containing xyz pts, and
another containing polygons. I am wondering if there is a way to use a
sql query to find the average elevation for a given polygon?
In GRASS 5 I don't know, but in GRASS 6 you can simply use
v.stats.rast which is giving you these results in a single step
(without learning SQL 
http://grass.itc.it/grass61/manuals/html61_user/v.rast.stats.html
I am trying right now to use MapInfo to do this query, but it doesn't like
the amount of points I am query (> 1,500,000) and knowing that GRASS is
much better at processing and dealing with larger files, wondered if a
query like this is possible..
I think that GRASS should work with 3 million points and more.
Markus