[OSGeo-Discuss] Quick hello and request for assistance finding Open Source

Peter Batty peter.batty at gmail.com
Thu Dec 3 15:26:18 PST 2009

Simon, you could do this as a PostGIS query. To take the polygon case, if
you loaded the data into a table in PostGIS called parcel (say), you could
run a query something like the following (not guaranteeing this is exactly
correct but something along these lines):

select a.id, b.id,
ST_distance(a.geom, b.geom),
ST_distance(ST_centroid(a.geom), ST_centroid(b.geom)),
ST_azimuth(ST_centroid(a.geom), ST_centroid(b.geom))
from parcel a, parcel b

This would give you ids, shortest distance, distance between centroids and
angle between centroids. There are no doubt others here who can correct my
SQL syntax :) !

There is a simple utility to load a shape file into PostGIS.


On Thu, Dec 3, 2009 at 3:49 PM, Simon Cropper (Botanicus Australia Pty Ltd)
<scropper at botanicusaustralia.com.au> wrote:

>  Hi Everyone,
> My name is Simon and I am an environmental consultant. I use a variety of
> open source GIS systems and tools almost every day to analyse flora, fauna
> and vegetation data. I am interested in OSGeo both from the standpoint (or
> my underlying belief) that software and data should be free (you know how
> the mantra goes) and my desire to contribute to a broader community effort
> to develop appropriate software for users. I have been actively using
> OpenJUMP, Kosmo, OpenEV, EveryDWG and Sextante. I have tinkered with Ilwis,
> GRASS, Quantum (various versions) and a few others I have lost track of. I
> am currently using GVSIG+Sextante, which I find very useful and easy to use.
> I am an old user of ArcView 3.1+(numerous scripts/extensions).
> I have a common GIS problem but can not find any OSGeo project that has
> provided a set of tools to combat it. I need to establish the distance+angle
> between various geometries (points, lines, polygons) in same layer and in
> different layers. A specific problem I currently have is finding the minimum
> distance and angle between 200 odd polygons in the same layer. Each polygon
> has a unique id and I want to get a table with UID_A, UID_B,
> MINIMUM_DISTANCE, ANGLE. I know that ArcGIS and ArcView have this
> functionality, and script exist for old versions of ArcView, but I am
> looking for an Open Source alternative.
> Ideally such a tool would create the following data for each geometry
> type...
> What I have found already...
>    - I have noted that Sextante can create a matrix of distances between
>    points within the same layer. With rows and column representing the complete
>    set of points being compared.
>     - I have also found QGIS has a fTools Plugin that allows you to
>    "Measure distances between two point layers, and output results as a) Square
>    distance matrix, b) Linear distance matrix, or c) Summary of distances."
>    QGIS 2009.
>     - I suspect that GRASS would provide this functionality but can't get
>    that package to work on my system (even WinGRASS), so if you point me here
>    please also point me to a tutorial on getting the thing to work (this system
>    is not intuitive; My problem has been in establishing a repository and
>    getting data into it for viewing, let alone analysis; it failed the age old
>    test that if you can't even get the thing running in half an hour, the
>    learning curve is going to be way too high to use in in normal business
>    activities; I have tried - yes following their instructions - several times,
>    and spent several days reading manuals, wiki's,etc to no avail).
> BUT I can't find any tool that allows me to calculate the minimum distance
> between polygons and indicate the direction of the polygon.
> Anyone out there know of such a tool?
> Note: I am using Windows XP Pro SP3 and store all my GIS data as
> shapefiles.
> --
> Cheers Simon
> Simon Cropper
> Botanicus Australia Pty Ltd
> PO Box 160, Sunshine, Victoria 3020.
> P: 9311 5822. M: 041 830 3437.
> mailto: scropper at botanicusaustralia.com.au<scropper at botanicusaustralia.com.au>
> web: www.botanicusaustralia.com.au <http://www.botanicusaustralia.com.au>
> _______________________________________________
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Peter Batty - President, Spatial Networking
W: +1 303 339 0957  M: +1 720 346 3954
Blog: http://geothought.blogspot.com
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