Subject: Re: elevation and geodetic system question
From: "J. Anthony Cavell, PLS"
Date: Wed, 08 Jan 1997 13:28:39 -0600
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Johan Eertink wrote:
>
> I was wondering whether or not to expect a change in elevation on maps
with
> different geodetic systems (e.g. ED50 vs. WGS84). I know that the
distance
> from the earth surface to the ellipsoid changes, but what about the
> elevation w.r.t. MSL (ANP in the Netherlands)?
>
> I would expect the MSL, and hence the elevation, to be completely
> independent of the geodetic system. Am I correct? Are there any good
sites
> on the web on this subject?
>
> --
> |
> Johan Eertink |
eertink@nlr.nl
> (These are personal opinions, they do not represent NLR's
view)
Dear Johan:
As you have defined it, elevation would not change because to be
elevation you have chosen MSL (or ANP) which is a (vertical) datum.
--
J. Anthony Cavell, PLS _______ ______
Vice President /_____ / / @ \ /____ /
Navigation Electronics, Inc. /_____ /===(@ % @)===/____ /
200 Toledo Drive /______/ \ @ / /_____/
Lafayette, LA 70506 "G P S m a n"
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Johan Eertink wrote:
>
> I was wondering whether or not to expect a change in elevation on
maps with
> different geodetic systems (e.g. ED50 vs. WGS84). I know that the
distance
> from the earth surface to the ellipsoid changes, but what about the
> elevation w.r.t. MSL (ANP in the Netherlands)?
>
> I would expect the MSL, and hence the elevation, to be completely
> independent of the geodetic system. Am I correct? Are there any good
sites
> on the web on this subject?
>
> --
>
|
> Johan Eertink
|
eertink@nlr.nl
>
(These are personal opinions, they do not represent NLR's view)
Dear Johan:
As you have defined it, elevation would not change because to be elevation
you have chosen MSL (or ANP) which is a (vertical) datum.
--
J. Anthony Cavell, PLS
_______
______
Vice President
/_____ / / @ \ /____ /
Navigation Electronics, Inc. /_____ /===(@ % @)===/____ /
200 Toledo Drive
/______/ \ @ / /_____/
Lafayette, LA 70506
"G P S m a n"
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Subject: Re: Polaris Almanac Data
From: alvarez@nntp.best.com (Richard Alvarez)
Date: 9 Jan 1997 04:09:42 GMT
<>
Please clarify that.
<>
At the upper and lower culminations (upper and lower limits of
motion), Polaris appears to move horizontally. Thus the moments of upper
and lower culmination, hence their azimuths, are not precisely observable
unless you know your longitude, the time, and some form of RA or hour
angle information on Polaris. One saving grace is that for Polaris
observed from the temperate latitudes, azimuth changes so slowly that
slight time error may not be ruinous.
Elongation gives much better azimuth accuracy because Polaris appears
to move vertically, and therefore its azimuth can be determined
accurately. But for that, you need to know your latitude and Polaris's
declination in order to compute the azimuth at elongation. And of course
the sky must be dark at the time of one of the elongations.
Dick Alvarez
alvarez@best.com
Subject: Re: elevation and geodetic system question
From: FRAN WEST
Date: Thu, 9 Jan 1997 11:13:44 +0000
In article <5avhe5$oup@nlrgup_fddi.nlr.nl>, Johan Eertink
writes
>I was wondering whether or not to expect a change in elevation on maps with
>different geodetic systems (e.g. ED50 vs. WGS84). I know that the distance
>from the earth surface to the ellipsoid changes, but what about the
>elevation w.r.t. MSL (ANP in the Netherlands)?
>
>I would expect the MSL, and hence the elevation, to be completely
>independent of the geodetic system. Am I correct? Are there any good sites
>on the web on this subject?
>
>--
> |
> Johan Eertink | eertink@nlr.nl
> (These are personal opinions, they do not represent NLR's view)
GEODETIC SYSTEMS ALL CARRY DIFFERENT SHIFT PARAMATERS WITHOUT GOING INTO
TOO MUCH DEPTH. SO YES, YOUR ELLIPSOIDAL HEIGHT WILL CHANGE BY SHIFTING
DATUMS, AS WILL THE DMSL. THE MSL HEIGHT SHOULD REMAIN CONSTANT,
PROVIDING THE SAME GEOIDAL MODEL APPLIES EG.STANAG
--
FRAN WEST
