|
|
Subject: Re: La Canoa datum
From: Paul Hirose (paulhirose@XXX.XXX)
Date: Wed Sep 26 2001 - 03:32:44 EDT
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@XXX.XXX (Paul Hirose)
|