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Re: (meteorobs) Which 'datum' to use for meteor report longitude and latitude
At 09:53 PM 6/7/00 -0400, Lew Gramer wrote:
>
>
>(Folks may argue that such accuracy is not necessary for visual observing,
but
>since I've never heard a definite statement to that effect from IMO, I always
>try to report my position within a second of arc and ten meters elevation.)
University of Texas - Austin Geography department has a nice discussion of
geodetic datums at:
http://www.utexasdot edu/depts/grg/gcraft/notes/datum/datum_ftoc.html
My Garmin GPS has a list of 40 or 50 different datums I can select from.
I've never used anything but WGS-84, but I can see the usefulness of
selecting others if working from older information or maps.
Needed accuracy is directly related to what use will be made of the
information. In individual visual observations, I don't see any real need
for accuracy greater than the nearest degree, to be quite honest (I report
to the nearest tenth of a minute, by the way). The position will be used to
compute an average radiant elevation for the observing period in order to
calculate ZHR. No great need for extreme accuracy there.
When considering two-station work, it is obviously more critical, and
obviously both stations should be using the same datum when figuring where
they are! I have no idea how much difference it would make in calculating
the parameters of an observed meteor if the two stations moved their whole
plane of reference (ellipsoid of reference?) this way or that a couple
hundred meters. Some of our more experenced readers can address that,
perhaps.
Jim B.
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