Yes, that is an oops. I think I'll go with Cliff's. He's the Chief of Geodesy, and I've got a degree in marine biology. I even got the scale factor wrong!
Dan Bowles BSc GIS Officer Harper Somers O'Sullivan PO Box 428 HAMILTON NSW 2303 E [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> T 02 4961 6500 M 04 3834 8372 -----Original Message----- From: Clifford J Mugnier [mailto:[EMAIL PROTECTED] Sent: Tuesday, 9 November 2004 9:11 AM To: Dan Bowles Subject: RE: MI-L Question for Real Surveyors Oops! It's just the other way around. Maximum UTM scale factor is 0.9996 at the Central Meridian, decreasing to unity as one approaches plus or minus 3 degrees from the central meridian. Clifford J. Mugnier Chief of Geodesy CENTER FOR GEOINFORMATICS Department of Civil Engineering LOUISIANA STATE UNIVERSITY Baton Rouge, LA 70803 Voice and Facsimile: (225) 578-8536 [Academic] Voice and Facsimile: (225) 578-4474 [Research] ================================ http://www.ASPRS.org/resources.html http://www.ce.LSU.edu/~mugnier/ ================================ Bill I work at a survey firm so have forwarded your email around for a response, hopefully you should get one soon. I would suggest that your problem is to do with scale factor. For example with a 6 degree UTM projection, the scale factor at the central meridian is 1 so you will have no distortion. However, at the edge of the zone the scale factor could be 0.994, meaning that for every 1000 m you measure you'll be 6 m out from the real position of your measurement. In NSW, where I live, surveyors use a 2 degree TM system to create a more accurate projection, at the edge of these zones the scale factor may be 0.9994. So for every 1000 m measured you'll only be 0.6 m out. A much more effective result. See below for our surveyors answer. Lazy bastards only use cartesian, but it's certainly a good way of solving the problem. Dan, In most of the surveys which we undertake we do not worry about the curvature of the Earth. This includes surveys up to 3 km's in the length of boundaries etc. This would provide a zero misclose in the quoted case. Cooko Dan Bowles BSc GIS Officer Harper Somers O'Sullivan PO Box 428 HAMILTON NSW 2303 E [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> T 02 4961 6500 M 04 3834 8372 --------------------------------------------------------------------- List hosting provided by Directions Magazine | www.directionsmag.com | To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] Message number: 13962
