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/ --------------------------------------------------------------------- List hosting provided by Directions Magazine | www.directionsmag.com | To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] Message number: 11905
