Thank you to everybody that has sent a
response to this question. Most of the response contained the question ‘why
isn’t the MapInfo procedure enough’. Well, we are a Transport
Consultancy and what we want is a point that represents the centre of a zone in
terms of the ease of transport in and out of the zone to a representative central
point. That point does not actually have to be within the zone as long as it
represents the centre. The MBR approach does not give a representative point,
for example if the zone is triangular, but gives a point that is good enough
for labelling. Therefore, the ‘balance point’, as Eric Johnson correctly calls it, is what we
require.
It seems that there is no
automatic MI method of doing this, so I’ll look in detail at the various
suggestions and decide if the effort will be worth the reward.
Thanks again for all your
suggestions,
Stephen
Stephen Marsh
Direct Line: +44 (0)20 7087 8737
Switchboard: +44 (0)20 7087 8700
-----Original
Message-----
From: Carlo Fazio
[mailto:[EMAIL PROTECTED]
Sent: 16 October 2006 03:12
To: Phil Waight; Marsh,
Stephen; mapinfo-l@lists.directionsmag.com
Cc: Obregon,
Alejandro
Subject: Re: [MI-L] How to find
the "Centre-of-Gravity" of a Region
Sorry, forgot
the page regarding my last email:
Phil Waight
<[EMAIL PROTECTED]> wrote:
I have a definition of 3 polygon
centroid types here (shifted centroid, geometric centroid, visual
centroid):
Some more examples and some rules to
determine the best choice of centroid for labelling, including calculation of
the principal axis for alignment:
The region geometric properties
functions are free-use and available from a button pad:
The primary use of the alternative
centroids noted in spatialSQL is to find valid alternative points for
labelling. As can be seen in the examples the choice of one type only would not
produce the best results. All computed values are stored
in columns in the target table.
There are application areas where
the geometric centroid or visual centroid could be of use in their own right.
The visual centroid is computed with an output radius of the "largest
circle to fit" and thus could be used in an SQL to determine
that a chosen polygon and v. centroid satisfy a "minimum distance to
neighbour" criteria (habitat?, agriculture?)
----- Original Message -----
Sent: Thursday,
October 12, 2006 11:22 PM
Subject: [MI-L] How
to find the "Centre-of-Gravity" of a Region
Does anybody know how to find the
“Centre-of-Gravity” of a region using MapInfo? The centriod
location is based on the ‘Minimum Bounds Rectangle’ approach, so
the centriod location is not the centre-of-gravity of the region. Also, the
centriod can be moved for presentation purposes etc. This means that the
coordinate extractor tool does not work for my purposes.
Any help in this matter will be
greatly appreciated!!
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