[R-sig-Geo] FW: [STATSGRASS] Questions on calculating minimum dista ncebetween polygons and map attributes after m.in.e00

[Roger Bivand]

On Mon, 15 Dec 2003 White.Denis at epamail.epa.gov wrote:

> I am a new member of r-sig-geo and saw your message in
> the archives.  I don't know whether you already had
> algorithms in mind, or received some responses on this,
> but two publications with algorithms are:
> 
> Chin F, Wang CA.  1983.  Optimal algorithms for the
> intersection and the minimum distance problems between
> planar polygons.  IEEE Transactions on Computers,
> Vol C-32(12):1203-1207.
> 
> Okabe A, Miller HJ.  1996.  Exact computation methods for
> calculating distances between objects in a cartographic
> database.  Cartography and Geographic Information Systems
> Vol 23(4):180-195.
> 

Thanks for interesting references. In other email (I think offlist, but
repeating here to get further response), the idea of using OpenGIS
functions on a database was floated:

http://www.mysql.com/doc/en/Functions_that_test_spatial_relationships_between_ge
ometries.html

(para 10.5.6 in MSQL Manual 4.1) describes a function:

Distance(g1,g2) Returns as a double-precision number the shortest distance
between any two points in the two geometries.

I'm not sure whether this supports latlong. PostGIS also has the same
function as an OpenGIS function.  http://postgis.refractions.net/ has the
details:

Distance(geometry,geometry) Return the cartesian distance between two
geometries in projected units.

It also has:

distance_spheroid(point, point, spheroid) Returns linear distance between
two lat/lon points given a particular spheroid. See the explanation of
spheroids given for length_spheroid().  Currently only implemented for
points.

as a non-OpenGIS function. Kristian's question is about nation states, so 
latlong is an issue, I believe. This makes it non-trivial, of course!

Any other ideas?

Roger

> > What I would like to do is to try to use an algorithm
> > to determine the shortest distance between points on
> > two states’ outer boundaries, with each state defined
> > either as a polygon or union of polygons.
> 
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-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Breiviksveien 40, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 93 93
e-mail: Roger.Bivand at nhh.no