[NatureNS] Determining Elevation

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Date: Wed, 7 Mar 2007 10:41:27 -0800 (PST)
From: Paul MacDonald <paulrita2001@yahoo.com>
To: naturens@chebucto.ns.ca
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Hi Tom
Thanks for the info. I often wondered what those
things meant. 
In addition I looked into GPS measuring of elevation.
I find they do so by atmospheric pressure. The GPS
sends that to the satelite which in turns takes the
pressure at the nearest airport and calculates the
elevation for the GPS. Seems atmospheric pressure at
airports is fairly important.
In this way weather variations are taken into account
- but if a weather system is going through Lunenburg
for example the Halifax airport reading will vary
somewhat. The claimed possible variation is 10 feet -
which is not too bad unless you are flying an
airplane!
An interesting subject.
Thanks again
Paul


--- Terri Crane <terri.crane@ns.sympatico.ca> wrote:

> Elevations are measured above "Highest High Water",
> "Large Tides" and is
> often refered to (atleast in the marine world) as
> "DATUM". Determined by the
> Canadian Hydrographic ????? (last part of their name
> escapes me) surveyors
> for that area. Our coastline is riddled with
> hydrographic survey pins from
> witch act as the bench/starting point for subsequent
> measurements. A quick
> glance at any Marine Chart will show the placement
> of these pins as a dot
> within a triangle and a height given along side. In
> almost all communities
> there is a stone (sometimes within the foundation of
> a large stone or brick
> building) in witch a brass pin is placed and this is
> the so called "Bench
> Mark" (on charts depicted as a dot within a circle
> with a discription). In
> Canso our "Bench" is located in the foundation wall
> of the Old Post Office.
> 
> Hope this helps
> All the Best
> Tom K.
> Hoping that this is the last blast of winter.
> 
> 
> ----- Original Message ----- 
> From: "Paul MacDonald" <paulrita2001@yahoo.com>
> To: <naturens@chebucto.ns.ca>
> Sent: Wednesday, March 07, 2007 10:45 AM
> Subject: Re: [NatureNS] Determining Elevation
> 
> 
> > Hi All
> > We had a very interesting discussion on this
> subject
> > recently which I follewed with interest.
> > One question remains for me. Just how is sea level
> > defined? High tide, low tide or the mean. If sea
> level
> > rises or falls does that throw the maps off?
> > Enjoy the late winter.
> > Paul
> >
> >
> >
> >
> >
> >
>
____________________________________________________________________________
> ________
> > Get your own web address.
> > Have a HUGE year through Yahoo! Small Business.
> > http://smallbusiness.yahoo.com/domains/?p=BESTDEAL
> 
> 



 
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