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_geometries.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

Roger Bivand

Department of Economics

Norwegian School of Economics

Helleveien 30

N-5045 Bergen, Norway