Surely you need trig points? http://www.trigpointinguk.com/info/trigpoints.php They'll only get you accuracy to a few centimetres though, not millimetres.
[http://www.itn.co.uk/images/ITN_Master_blue.gif] PHILLIP BARNETT SERVER MANAGER 200 GRAY'S INN ROAD LONDON WC1X 8XZ UNITED KINGDOM T +44 (0)20 7430 4474 F E [email protected] WWW.ITN.CO.UK<http://WWW.ITN.CO.UK> P Please consider the environment. Do you really need to print this email? ________________________________ From: [email protected] [mailto:[email protected]] On Behalf Of John Robert Peterson Sent: 22 June 2010 21:33 To: talk-gb OSM List (E-mail) Subject: [Talk-GB] Reference points for total station I have managed to gain access to a total station (http://en.wikipedia.org/wiki/Total_station) for doing a survey of a built up university campus. The goals of the project are 2 fold: 1) learn some new skills 2) get some decent data for OSM of the area. Now for anyone that doesn't know about these things, they measure angles horizontally with a very precise optical system, and use an IR range finder beam to locate a reflector prism to within millimeters. It's range is into the hundreds of meters. It has a sophisticated processing unit in it that can do some helpful maths and data storage for you. The prism is on top of a stick of measured length, with a spirit level built in, and is carried and placed by an assistant known as a "stick monkey". It's well known to that that actually know what they are talking about in these circles, that positioning the stick is actually the talented part of the operation and that repeatedly pressing the green button on the box is actually less intellectually demanding. There is also a "reflectorless" version that I may be able to gain access to later, but that's not guaranteed. This uses lasers, and requires no "stick monkey" and associated gibbons. The plan is to use this for heights of buildings only. The device provides accurate 3d positions with the following caveat: it has no idea where it is, or where it's pointing until it gets reference data, this can be done in the following ways: It knows where down is via gravity; If you give it a number of calibrated reference points, it can work out where it is and where it's pointing, error control is built into this, so it needs at least 3, preferably 5 points, one of the points needs to have proper altitude; If you once get it calibrated, you can generate more calibrated reference points, meaning that you can daisy chain it off itsself; Since this is a learning process into surveying, we want to actually do it to an accuracy of a few millimeters. So the question is -- where do we get the first points from? There is one very old and well known building right in the middle of the area, and there are a number of land marks around, these may be usable, but how do I know their positions? There are also a number of distant landmarks in the area, but most would be too far away to use effectively, I dont' think the machine has the ability to take points only as distant points with no distance, though I do have access to the raw data, and would happily do the maths myself. Thanks, JR Please Note: Any views or opinions are solely those of the author and do not necessarily represent those of Independent Television News Limited unless specifically stated. This email and any files attached are confidential and intended solely for the use of the individual or entity to which they are addressed. If you have received this email in error, please notify [email protected] Please note that to ensure regulatory compliance and for the protection of our clients and business, we may monitor and read messages sent to and from our systems. Thank You.
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