Re: How to return latest results without a polygon intersect?

Thank-you for the help.

I defined the problem a little better and took your advice and asked in
postgis users:
http://www.postgis.org/pipermail/postgis-users/2012-January/032056.html

Dave

On Wed, Jan 11, 2012 at 11:20 PM, Andy Colson <andy(at)squeakycode(dot)net> wrote:

> On 01/11/2012 07:14 PM, David Waddy wrote:
>
>> If I have a table of the following form:
>>
>> id (integer) event_time (timestamp) lat_lon (polygon)
>> 3497 1977-01-01 00:00:00
>> ((-64.997,45.975),(,(-64.9981,**45.975),(-64.8981,45.875),(-**
>> 64.9978,45.9751))
>> 3431 2007-06-06 01:00:00
>> ((-64.971,45.982),(-64.921,45.**982),(-64.972,45.982),(-64.**
>> 973,45.98209),(-64.97,45.**98237))
>> 3498 1977-01-01 00:00:00
>> ((-64.97838,45.9778),(-64.**9783,45.97767),(-64.978,45.**
>> 977),(-64.9781,45.97728),(-64.**9781,45.97714),(-64.977,45.**976))
>> ...
>>
>> How would I return a list of the latest events for a particular
>> lat/lon region? More precisely, how would a return a result set with
>> the greatest event times with polygons that don't intersect any other
>> polygon in the result set?
>>
>> Any help would be greatly appreciated,
>> Dave
>>
>>
> Are you using PostGIS? Assuming yes, try something like:
>
> select * from theTable a cross join theTable b on not (a.lat_lon &&
> b.lat_lon) order by event_time
>
> Also try the postgis news group, there are people there with more
> experience with the postGIS functions.
>
> Your two questions dont seem to be asking the same thing, though. One
> asks for a particular region. The second for a region that doesn't
> intersect with any other's. I went for the second, cross joining the table
> to itself, so every record with be compared to every other record, which is
> gonna be a huge number of comparisons. So it'll be slow.
>
> -Andy
>

--
David Waddy
Waddy & Colpitts Ltd.
99 Milky Way
Colpitts Settlement, NB
E4J 0B6 Canada
tel: 506-372-4564
http://www.littleriver.ca