I have been deliberating whether to post this to the list for some time but decided to 'bite the bullet' and fire away! It is regarding the datum number associated with Australian Geodetic 1966 (AGD66) and Australian Geodetic 1984 (AGD84) being 12 and 13 respectively (see below copied from mapinfow.prj file). "--- Australian Map Grid (AGD 66) ---" "AMG Zone 50 (AGD 66)\p20250", 8, 12, 7, 117, 0, 0.9996, 500000, 10000000 "--- Australian Map Grid (AGD 84) ---" "AMG Zone 50 (AGD 84)\p20350", 8, 13, 7, 117, 0, 0.9996, 500000, 10000000
AGD66 results from the network adjustment of geodetic observations to 1966, based on the ANS. AGD84 corrects deficiencies shown to exist in the AGD66. What I cannot understand is, seeing that both these numbers use the same Australian National spheroid (ANS) what would the difference be in the parameters used in the projection statement and how can you find this out? If for instance you save an AMG Zone 50, AGD66 table of points to an AMG Zone 50, AGD84 table, the adjusted coordinates show the small difference between the coordinate systems but underlying all this is the fact that they both use the same spheroid and all we are dealing with here is an adjustment due to a better geodetic model brought in about 1982. A work colleague of mine is adamant that MapInfo is wrong to apply two different datum numbers due to the above and believes MapInfo deals with this incorrectly. I do not understand his logic. Can anyone possibly clear my mind on this issue? Regards Chris Chris Brown - Cartographer Resources Planning, Hamersley Iron P/L Tel. +61 8 9327 2176 Fax. +61 8 9327 2478 mailto:[EMAIL PROTECTED] ---------------------------------------------- This email (including all attachments) may be confidential. If you are not the intended recipient, you must not use the information contained in it. If you have received this email in error, please delete the email and notify the sender. --------------------------------------------------------------------- List hosting provided by Directions Magazine | www.directionsmag.com | To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
