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Hi Gang A word of caution to anyone using a GPS to get a measurement of elevation. It's more of a crap shot guess than anything of any accuracy to be useful! I have owned one for years and used a few other brands and in my opinion they ALL fail at the task of determining accurate elevation. While on board my boat I've seen my position interpreted as being as high as 110' above sea level. Did anyone see that tidal wave go by? And I was on its crest for the whole day! A relatively quick test on my back step showed me that my house had an elevation of between 25m and 37m this was the min and max that I noted over ~ 1h. The given elevation was never a constant for more than a min. at a time during my 6-7, 2 min. observations. This equates into a 12m or 39' +/- fluctuation of elevation of my feeder on my deck. AHHH, I Don't Think So! This is due to the errors that contaminate the signals and limitations of the interpretive programs within the receivers. Of course all this error is intentionally left/put their by "Big Brother, Uncle Sam,.......". Tom K. Canso ----- Original Message ----- From: "Paul MacDonald" <paulrita2001@yahoo.com> To: <naturens@chebucto.ns.ca> Sent: Wednesday, March 07, 2007 2:41 PM Subject: Re: [NatureNS] Determining Elevation > 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 > > > > > > > > > ____________________________________________________________________________ ________ > Expecting? Get great news right away with email Auto-Check. > Try the Yahoo! Mail Beta. > http://advision.webevents.yahoo.com/mailbeta/newmail_tools.html
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