-----Original Message-----
[mailto:[EMAIL PROTECTED]]On Behalf Of Curt Newsome
Sent: May 11, 2000 12:15 PM
Subject: Re: MI. Measuring distancce
....
This should work - the distance function is very poorly documented in the
MapInfo help files/books.
....
Here is some information printed in the MI Professional 5.5 supplement (and
present in the 5.5 help files) that makes it almost clear how distance is
calculated.
DISTANCE()
If the current coordinate system is an earth coordinate system, Distance(�)
returns the great-circle distance between the two points. A great-circle
distance is the shortest distance between two points on a sphere. (A great
circle is a circle that goes around the earth, with the circle's center at
the center of the earth; a great-circle distance between two points is the
distance along the great circle which connects the two points.)
For the most part, MapInfo performs a Cartesian or Spherical operation.
Generally a Spherical operation is performed unless the coordinate system is
NonEarth, in which case a Cartesian operation is performed.
SPHERICALDISTANCE()
The SphericalDistance( ) function always returns a value as calculated in a
Latitude/Longitude non-projected coordinate system using great circle based
algorithms.. A value of -1 will be returned for data that is in a NonEarth
coordinate system since this data can't be converted into a
Latitude/longitude coordinate system.
CARTESIANDISTANCE()
If the current coordinate system is an earth coordinate system,
CartesianDistance(�) returns the great-circle distance between the two
points. A great-circle distance is the shortest distance between two points
on a sphere. (A great circle is a circle that goes around the earth, with
the circle's center at the center of the earth; a great-circle distance
between two points is the distance along the great circle which connects the
two points.)
If the current coordinate system is a non-earth coordinate system,
CartesianDistance(�) returns the Cartesian distance.
Now, you may want to know the algorithm used to calculate it along a
great-circle... but that is above my head and not within my interests.
Jacques Paris
e-mail alternate
[EMAIL PROTECTED] [EMAIL PROTECTED]
paris PC Consult (mainly MapInfo app.)
www.total.net/~rparis/gisproducts.htm
----------------------------------------------------------------------
To unsubscribe from this list, send e-mail to [EMAIL PROTECTED] and put
"unsubscribe MAPINFO-L" in the message body, or contact [EMAIL PROTECTED]
