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Subject: RE: [Nml] Spherical earth model vs. ellipsoid
From: Daniel K. Allen (Visual C++) (danallen@XXX.XXX)
Date: Mon Mar 15 1999 - 16:59:09 EST
See http://indigo.ie/~topcon/products/surveying/theodolites/index.html for
more details on this theodolite, which is guaranteed to an accuracy of 2
seconds ("Standard deviation based on 18723") of arc, some six times what
the best C. Plath sextants do. They use a 30 power scope and some models
are waterproof!
Dan
-----Original Message-----
From: Henning Umland [mailto:h.umland@XXX.XXX]
Sent: Monday, March 15, 1999 1:43 PM
To: navigation@XXX.XXX
Subject: Re: [Nml] Spherical earth model vs. ellipsoid
Date sent: Mon, 15 Mar 1999 13:07:11 +0100
From: Jim Manzari <manzari@XXX.XXX>
Organization: am Buck
To: navigation@XXX.XXX
Subject: Re: [Nml] Spherical earth model vs. ellipsoid
Send reply to: Jim Manzari <manzari@XXX.XXX>
>
> Henning,
>
> I was intrigued by your test. It appears to have been well planned
> and executed. Thanks for posting a very interesting summary of the
> results.
>
> You've expressed a doubt as to whether the method may be applied
> elsewhere in the world. Perhaps my experience in a similar experiment
> might give you some food for thought.
Jim,
When I made my experiments, I was aware that the spirit level can
be deflected by local anomalies of the earth's surface like ,e.g., ore
deposits, mountains, lava plugs, etc.
Fortunately, the area southeast of Hamburg is absolutely flat, the
ground consists only of clay, sand, and pebbles deposited by
glaciers, and we don't have ores and other heavy minerals here.
I was thinking of geometric anomalies in other parts of the world,
for the earth is not really an ellipsoid but has a rather irregular
shape with local depressions and the like. I once saw an image
showing the exaggerated irregularities of the earth. It looked like a
dented apple.
The theodolite I have is a TOPCON DT-102. It is an electronic
model with a built-in microprocessor and digital display. Further, it
has an electronic tilt compensator which is a very useful device
since the legs of the tripod sometimes change their length to a
different degree when irradiated by the sun (otherwise you would
have to adjust the spirit level repeatedly).
Although mostly used for surveying, theodolites are valuable
instruments for celestial navigation as well (on land only!). Due to
their superior precision they are the first choice when doing
"academic" studies.
Regards,
Henning
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