The elevation accuracy of commercial GPS units is horrible, I've seen them off by more than 100 feet and they are not reliable at all for the requested usage in this instance. Surveyors use GPS units that are accurate in both horizontal and vertical axis measurements but they use radio frequency units to get down to accuracy levels within inches on either.
My suggestion is to contact a manufacturer of surveying equipment and asking them for technical information on how their units achieve high degrees of accuracy. But be advised, they are very expensive. Tom ----- Original Message ----- From: Peter Parrish To: 'RE-wrenches' Sent: Tuesday, January 27, 2009 12:32 PM Subject: Re: [RE-wrenches] GPS units A caution to all. There are various types of GPS units, with varying accuracies. The most accurate are spec'd at around +/- 6 feet. I have a Garmin Etrex and under normal circumstances it delivers at that spec or better (+/- 3 feet). Near tall buildings or in a steep canyon, the accuracy goes to pot but for known reasons (multiple reflections of the radio signals). I have no manufacturer's info on elevation, but knowing how GPS units work, the resolution/accuracy in elevation should be roughly the same. - Peter Peter T. Parrish, President California Solar Engineering, Inc. 820 Cynthia Ave., Los Angeles, CA 90065 Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885 CA Lic. 854779, NABCEP Cert. 031806-26 peter.parr...@calsolareng.com ------------------------------------------------------------------------------ From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Jason Lombard Sent: Tuesday, January 27, 2009 2:02 PM To: RE-wrenches Subject: Re: [RE-wrenches] GPS units William, Topographic maps are great if your familiar with them. A laser if you can afford it or the best I have heard of is fill a tube or pipe with water from the pump to your tank and measure the psi at the base of it. The calculation is 2.31 feet of lift for every psi. Not everyone has their piping rolled out or on site yet so this could be a challenge and again is very accurate. BTW - GPS units are inaccurate to the extent that they are 40 feet off horizontally and 90 feet vertically. This means you could be up to 130 feet off. Big difference when your sizing for particular pump out put. Good luck, On Tue, Jan 27, 2009 at 2:34 PM, William Miller <wrmil...@charter.net> wrote: Does anyone have a foolproof tool to measure elevation? I have researched GPS units recently. They are notoriously inaccurate for elevation: http://wiki.motionbased.com/mb/GPS_Unit_Elevation Here are few more links with GPS fundamentals: http://www.adventurenetwork.com/cgi-bin/adventurenetwork/GPS_101.html http://www.gpsreview.net/electronic-compass/ I have a Suunto Observer watch with an altimeter. I think I can get relatively accurate measurements of DIFFERENCE in elevation if I measure the two elevations in quick succession. I will be trying it. William _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org -- Jason Lombard Open Hand Solar LLC. Certified Sustainable Building Adviser openhandso...@gmail.com 505 795 8646 "I'd put my money on solar energy. I hope we don't have to wait 'til oil and coal run out before we tackle that." -Thomas Edison ------------------------------------------------------------------------------ _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org ------------------------------------------------------------------------------ No virus found in this incoming message. Checked by AVG - http://www.avg.com Version: 8.0.176 / Virus Database: 270.10.14/1917 - Release Date: 1/26/2009 6:37 PM
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