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Re: La Canoa datum
From: Paul Hirose
Date: 2001 Sep 26, 1:33 AM
From: Paul Hirose
Date: 2001 Sep 26, 1:33 AM
I did some detective work and found clues to this "La Canoa" business in the Explanatory Supplement to the Astronomical Almanac. The table of geodetic datums has this entry: Datum: Provisional S. American 1966 Ellipsiod: International Origin: La Canoa Latitude: +08 34 17.17 Longitude: 296 08 25.12 Astronomers measure long. eastward to 360. Datum of the origin coordinates isn't specified in the table. The table of ellipsoids on the facing page has this entry: Ellipsoid: International 1909 Semi-Major Axis (m): 6378388 Inverse flattening: 297 An appendix in my Magellan ProMARK GPS receiver manual lists a slew of datums all over the world. There's no Provisional South American *1966* there, but there is a *1956* using the International ellipsiod. Typo? I used the receiver's South American 1956 datum to check Aubrey's WGS84 vs. La Canoa coordinates. Looked good! Latitude missed by 0.05" and longitude by 0.03". The ProMARK's South American 1956 transformation is a compromise giving a best fit over a huge multi-nation area. The manual's appendix breaks it down to smaller zones (one of which is Venezuela) and gives parameters optimized for each zone. These can be loaded manually for higher accuracy. Tomorrow (uh, later today when I wake up) I'll try that and report results. -- paulhirose@earthlink.net (Paul Hirose)