In general, GPS vertical resolution is less than horizontal and for accurate levelling optical devices are still recommended. However, it does depend on the GPS unit and the more expensive 'professional' surveying units, e.g., Trimble, are substantially more accurate than the cheap Garmin devices. One comparitive study done in Wales found huge inaccuracies in the Garmin height measurements and their horizontal accuracy doesn't seem particularly special either.
It also depends upon the exact configuration of the system, with Trimble apparently recommended for the measuring system itself. Some units have a dual network capability which can also increase overall resolution - the ones I have come across use either Russian satellites or American, or both in some cases. When using both there is apparently an increase in precision (all the time? location?) but I have no direct experience to draw on here. One comment addressed particularly to Bob Pope - how does he know that his measurements were within centimeters? Have you any comparison data that you could tell us more about for the Trimble system? Martin Roseveare p.s I have no links with any GPS manufacturer! ______________________________________ ArchaeoPhysica Ltd. Reconnaissance & Geophysics for Archaeology Telephone: +44 (0) 7050 369789 E-mail: [EMAIL PROTECTED] Website: http://www.archaeophysica.co.uk ______________________________________ This e-mail is intended only for the addressee named above and may contain confidential or privileged information. If you receive this e-mail by mistake please advise the sender and destroy it without further disclosure of its content. Unless otherwise stated no opinions expressed in this e-mail should be regarded as representative of any policy of ArchaeoPhysica Ltd. ----- Original Message ----- From: "Bob Pope" <[EMAIL PROTECTED]> To: "Mahmut GETIN" <[EMAIL PROTECTED]> Cc: <[EMAIL PROTECTED]> Sent: Monday, November 18, 2002 11:19 PM Subject: RE: AI-GEOSTATS: GPS Device We recently completed a year-long environmental assessment project of a rugged three-mile property with hundreds of structures and thousands of exploration locations. We used a Trimble 5700 to locate all of the structures and exploration locations. Our accuracy was within centimeters. Our results were reliable and reproducible. I highly recommend this technology. See: www.trimble.com <http://www.trimble.com/> Best, Bob Robert Pope Senior Hydrogeologist Waterstone Environmental, Inc. Anaheim California (714) 414-1122 x210 -----Original Message----- From: Mahmut GETIN [mailto:[EMAIL PROTECTED]] Sent: Saturday, November 16, 2002 4:52 AM To: [EMAIL PROTECTED] Subject: AI-GEOSTATS: GPS Device Dear list members, We are planning a field survey. In the field, we have many deep groundwater wells. We will determine both position and elevations of each well by using a GPS device. Do you think that we may measure the elevation by using GPS. What about the precision or error we are subject to? Could you recommend us a device with some specifications. Surfing Internet, I found GPS devices of GARMIN, however no specifications on elevation measurements. Every kind of suggestion is welcome. Yours Sincerely, Dr. Mahmut CETIN ------------------------------------------------------------------------ ------- Associate Prof. Dr. Mahmut CETIN Department of Agricultural Structures and Irrigation Faculty of Agriculture University of Cukurova 01330 Balcali-Adana/TURKEY Tel: ++90 (322)338 6877 (Direct) ++90 (322) 338 6318 (Switchboard, ext. : 25) Fax: ++90 (322) 338 6386 E-Mail: [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> -- * To post a message to the list, send it to [EMAIL PROTECTED] * As a general service to the users, please remember to post a summary of any useful responses to your questions. * To unsubscribe, send an email to [EMAIL PROTECTED] with no subject and "unsubscribe ai-geostats" followed by "end" on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list * Support to the list is provided at http://www.ai-geostats.org -- * To post a message to the list, send it to [EMAIL PROTECTED] * As a general service to the users, please remember to post a summary of any useful responses to your questions. * To unsubscribe, send an email to [EMAIL PROTECTED] with no subject and "unsubscribe ai-geostats" followed by "end" on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list * Support to the list is provided at http://www.ai-geostats.org
