Thanks Paul,
I will check out contrib/seg - it sounds like it might have
application for another (unrelated) issue I am dealing with. It's a
neat solution (as are most of these modules) to a problem.
cheers
Ben
On 20/02/2009, at 5:01 AM, postgis-users-
[email protected] wrote:
Date: Wed, 18 Feb 2009 16:35:06 -0800
From: Paul Ramsey <[email protected]>
Subject: Re: [postgis-users] Basic question #1 Managing temporality in
spatial data - MAUP over time
Your approach is fine.
If you were dealing with much larger data collection, you'd find that
over time your spatial selectivity starts to go down, as more and more
data piles up in the same x/y area over time. That's when it's time to
add an indexed time-range to your tuples, so that you can
simultaneously index select on spatial and temporal ranges. For that I
would suggest adding a time range column containing 'seg' objects (see
./contrib/seg) with the end values derived from unix timestamps.
Paul
On Wed, Feb 18, 2009 at 4:24 PM, Ben Madin <[email protected]
> wrote:
I hope no one minds this, but I have to deal with some changes to
my data,
and thought it might be a good opportunity to ask the basic
questions I've
been dwelling on for some time.
Having just received a new set of the spatial data I am working with
(shapefiles of administrative regions), I am unsurprised to find
that about
15 districts have gone (been amalgamated), some new ones appeared,
and
indeed one entire province removed!
My intention was to add two columns to my gis data table -
geom_start_validity & geom_end_validity, and revise my queries (which
normally are analysing / displaying movement information) to choose
the
appropriate geometry depending on the date range of the query.
Is the approach sound? (Is this a reasonable idea? Am I completely
off track
here? Will this make my table difficult to index? Should I find all
the
polygons which are the same and delete the duplicates, extending the
validity dates?)
(The interface which relates to the entry of movements would also
be amended
to deliver a different set of provinces and districts depending on
the date
of the movements. How I deal with movements that occur over the
transition
is beyond me so far!)
--
Ben Madin
REMOTE INFORMATION
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