[postgis-users] Comparing two Building Footprint Tables

[Clifford Snow]

I had considered using addressing data to give each footprint a unique id,
but yours does the same with one less step.  i'm going to try Rémi-C
solution as well.

Thanks


On Sat, Aug 23, 2014 at 3:51 AM, David Siegel <david.siegel at artcom.de>
wrote:

> Hi Clifford
>
> just a quick saturday morning thought: One approach is to use a hash
> function like SHA256. To get started I’d try something like this:
>
> 1. For each footprint get a text representation of the geometry
> 2. Compute and store the SHA256[1] hash of the text representation
> 3. Find those hash values that are unique to the new footprint table
>
> Note that you can influence the result by changing the text
> representation. Using a sorted list of just the coordinates for example
> ignores any changes in topology, &c. To speed things up just add an index
> on the hash column.
>
> Cheers,
>
> d
>
> [1] http://www.postgresql.org/docs/8.3/static/pgcrypto.html
>
> On 23.08.2014, at 00:49, Clifford Snow <clifford at snowandsnow.us> wrote:
>
> > The city of Seattle published a new shapefile with the latest building
> footprints. The previous file was from 2009. I'd like to find which
> outlines have changed. While I can see the differences using QGIS, what I
> need is a list of changed or new building footprints. I'm struggling where
> to start. There are about 300K footprints. The city did not retain any
> unique ids from the previous file to the new.
> >
> > Any suggestions would be appreciated.
> >
> > Thanks,
> > Clifford
> >
> > --
> > @osm_seattle
> > osm_seattle.snowandsnow.us
> > OpenStreetMap: Maps with a human touch
> > _______________________________________________
> > postgis-users mailing list
> > postgis-users at lists.osgeo.org
> > http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
>
> _______________________________________________
> postgis-users mailing list
> postgis-users at lists.osgeo.org
> http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
>



-- 
@osm_seattle
osm_seattle.snowandsnow.us
OpenStreetMap: Maps with a human touch
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/postgis-users/attachments/20140823/3fff24a3/attachment.html>