Ahmet,
The parameters you sent are an example of a MI projection file for
Luxembourg, and it is rather complicated. Bursa-Wolf is the name of a
mathematical model for performing transformations from one specific Datum
to another specific Datum. In this case, it refers to the transformation
from European Datum 1950 to the World Geodetic System 1984 (WGS84) used by
GPS satellites. The parameters are in meters and are earth-centered in
the Geocentric Coordinate System and refer to a dX,dY,dZ translation at the
center of the earth AFTER a three-parameter rotation RZ,Ry,Rx (in radians
or arc seconds) and an overall scalar (dimensionless) multiplication is
performed FIRST.
What is remarkable is that the "MI example file" is grossly incorrect!
That is indicated by the fact that only six of the seven parameters for a
Bursa-Wolf Transformation are given, (the Scale Factor is not even given),
and for the "(Simplified Bursa-Wolf)" it is an obvious truncation!!
This example file is an excellent lesson of what happens when programmers
and mathematicians try to play with Geodesy - they obtain the usual result;
a complete screw-up! Apparently unknown to some "computer jockeys," the
solution for the seven parameters of a Bursa-Wolf model or a
Molodensky-Basdekas model always involves a solution for the rotations and
the scalar FIRST - THEN the translation parameters are solved. That means
that the rotation parameters (and scale factor) may NEVER BE TRUNCATED!!!
To the neophyte (read "computer jock"), the rotation angles look so small
that they appear to be insignificant. However to one that works with the
math of the actual parameter solutions, one knows that the tiny rotations
are at the center of the earth! When you examine the effect at the surface
of the ellipsoid - the magnitude is quite substantial! Same thing goes for
the scale factor expressed as so many parts per million. Tiny numbers with
negative exponents, but when you consider the semi-major axis is
6,378+ kilometers; the effect is again quite substantial! Transformations
are affected by such blunders and resultant data will be grossly incorrect.
Therefore, in the "example MapInfo file for simplified Bursa-Wolf
parameters," the only thing simple is the simpleton that truncated the
critical parameters!
In regard to your local problem of implementing such data for your country,
I shall be happy to assist you in determining the appropriate parameters if
you send your data to me via e-mail. I will then solve for a 3-parameter
model, a 4-parameter model, and a 7-parameter model and provide you with
the accuracy results for each model solved.
Consider looking at some of my past columns on Grids and Datums of
different countries at:
http://www.ASPRS.org/resources.html
Please let me know if I may be of further assistance, and consider joining
the American Society for Photogrammetry and Remote Sensing (ASPRS).
Good luck!
Clifford J. Mugnier ([EMAIL PROTECTED])
Surveying, Geodesy, and Photogrammetry
LOUISIANA STATE UNIVERSITY
12408 CEBA Building
Baton Rouge, Louisiana 70803
Voice and Facsimilie: (225) 388 - 8536
----------------------------------------------------------------------
To unsubscribe from this list, send e-mail to [EMAIL PROTECTED] and put
"unsubscribe MAPINFO-L" in the message body, or contact [EMAIL PROTECTED]
