Old rant of non GIS people: cartographers live in 2D ! ;)
A higher dimension space, once projected onto a 2D display leads to this
kind of figure.
Let's take a 3D (2.5D ?) space... for example a *real* terrain. Project it
on a surface ... let say a map.
Use an isotropic projection, let say a 2D cartesian one.
The resulting surface is an isotropic projection of space: you reduced a
dimension, by flattenning the terrain.
Do the same projection on the surface with equidistant points measured on
the terrain, I mean in 3D (well, if you follow the roads, it's even more
than 3D, but KISS). That's an isotropic projection too, and leads to the
figure wanted (if I got it right), wich is not a circle ... but more like a
drop of marmalade on the kitchen table ...
Same thing happen if you project 4D on a map (taking time into account).
Well, I'd simply call it a projection. It would be circle in higher
dimensions space (more than 3D!...)
A hint : think 3D, it gives you one more dimension for your projections :
www.geovrml.com !
Eric.
Eric Maranne
EMI Informatiques : www.geovrml.com
(33)(+) 4 42 06 22 22
Port de Bouc - France :
http://www3.calle.com/info.cgi?lat=43.4000&long=4.9833&name=Port%2dde%2dBouc
&cty=France&alt=0
43� 23' 60N 4� 58' 60E Alt: 0
> -----Message d'origine-----
> De : [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED]]De la part de Spencer
> Simpson
> Envoy� : jeudi 13 septembre 2001 18:21
> � : Mapinfo Mailing List
> Objet : Re: MI-L RE: circles
>
>
>
>
>
> Brooks, Stephen wrote:
>
> > >I would like to know the name of a line that links all points of equal
> > >distance from a specific point. This is not necessarily just a circle
> > >around the point if you take into consideration permeability of route
> > >networks.
>
> "Bill Huber" <[EMAIL PROTECTED]> replied:
>
> > "Isometric curve" would be correct but I have never seen it used.
> >
> > The proper mathematical term really is "circle."
>
> <snipped description>
>
> > The terminological trick, then, is to specify what metric you mean:
> > Euclidean, spherical, or network. The phrase, "circle in the network
> > metric," or "network circle" for short, would be appropriate for the
> > latter. This gives us three kinds of circles, respectively: (ordinary)
> > circles, geodesic circles, and network circles.
>
> Well, yes and no. As the network space is a series of lines,
> a "network circle" is a collection of isolated points.
>
> Mr. Brooks may be interested in a figure arrived at when the network
> is embedded in a two-dimensional Euclidean space (i. e. it is displayed
> on a map) and the network "circle" points are connected to each other
> with lines across the new space. The lines do not serve any analytical
> purpose; they exist for cosmetic purposes only.
>
> HTH
> Spencer
>
>
>
> _______________________________________________________________________
> List hosting provided by Directions Magazine | www.directionsmag.com |
> To unsubscribe, send e-mail to [EMAIL PROTECTED] and
> put "unsubscribe MapInfo-L" in the message body.
_______________________________________________________________________
List hosting provided by Directions Magazine | www.directionsmag.com |
To unsubscribe, send e-mail to [EMAIL PROTECTED] and
put "unsubscribe MapInfo-L" in the message body.
