And the question to all this is ... ?
The only thing I can guess is that the "traverse" appears to be based on
calls that certainly are not ellipsoidal terms. Are these planar or
spherical? In either case, it's not going to work because the defining
surface figure is ellipsoidal.
Maybe the calls will work on a sphere ... try the orthodrome and not the
ellipsoidal geodesic.
If this were simple, it would not have been called the "Principal Problem
of Geodesy" in the 19th century.
Clifford J. Mugnier
Chief of Geodesy and
Associate Director,
CENTER FOR GEOINFORMATICS
Department of Civil Engineering
LOUISIANA STATE UNIVERSITY
Baton Rouge, LA 70803
Voice and Facsimile: (225) 578-8536
================================
http://www.ASPRS.org/resources.html
http://www.cee.lsu.edu/facultyStaff/mugnier/index.html
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-------------------------------------
Hello Listers
I'm sure someone is well-informed about this non-MapInfo question, and can
give me a ready answer.
Using the Vincenty FORWARD equation (compiled FORTRAN), a traverse as
follows misses its closure (origin) by over 3km -
Start point P1: -25/120 (25degrees South, 120 degrees East)
P1-P2: 040deg, 240,000m
P2-P4: 160deg, 100,000m
P4-P6: 220deg, 120,000m
P6-P3: 220deg, 120,000m
P3-P1': 340deg, 100,000m
The end point (P1') has a calculated lat/long of -24d59'15.85606" /
119d58'21.49343"
Using the Vincenty INVERSE equation (compiled FORTRAN) P1-P1' gives a
separation of 3078.33m approx, forward azimuth about 296deg
The compiled programs I am using are regarded as reliable (see below), and
to my knowledge (reading the Vincenty paper and NGS / NOAA comments) should
be accurate for the purpose - certainly, a 3km closure error means
something's not right here!
For Australia, I choose the options 3,C which uses the Australian National
Ellipsoid (which has a = 6378160.0000, and 1/f = 298.250000). From Appendix
G in the MapInfo user manual, this is the same as the Ellipsoid 2
(Australian).
IL Thomas
GeoSciSoft - Perth, Australia
Background on Vincenty formulae:
The "Vincenty formulae" were published in 1975, by Thaddeus Vincenty (an
American, I think), as a publication of the Directorate of Overseas Surveys
of the Ministry of Overseas Development (don't you love the old titles -
today it would be something jazzy and stupid like "Surveys UK"), as Survey
Review XXII, 176, April 1975, pp88-93.
This paper was the basis for 4 FORTRAN 77 programs (INVERSE, FORWARD,
INVERS3D, FORWRD3D) last compiled in 2002 by Stephen J. Frakes (and several
others, including Robert Safford, back as far as 1985) at NGS/NOAA, and
available for download (compiled, and as source-code) from
http://www.ngs.noaa.gov/PC_PROD/Inv_Fwd/
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