+ZoomZoom Posted February 16, 2003 Share Posted February 16, 2003 Heard the term before but I just don't know what it means. Can someone help me out with this? Quote Link to comment
+GEO*Trailblazer 1 Posted February 16, 2003 Share Posted February 16, 2003 http://webgis.wr.usgs.gov/gridpig.htm WHEN ALL ELSE FAILS *GEOTRYAGAIN* http://www.msnusers.com/MissouriTrails Quote Link to comment
+ron50eli Posted February 16, 2003 Share Posted February 16, 2003 Cool site. It's in my favorites now. Thanks. rocker51 Quote Link to comment
+Poindexter Posted February 17, 2003 Share Posted February 17, 2003 One way the term is used is in reference to USGS 7.5' topo maps. Most of these use the NAD27 datum but will indicate how much and in what direction to shift the grid to NAD83 datum. Quote Link to comment
+canadazuuk Posted February 17, 2003 Share Posted February 17, 2003 Grid shift is really misunderstood. and many folks tend to think they have a clue what it is... including me Basically, maps are flat, and the world is NOT. example- in the northern hemisphere the (south) bottom of a map may exactly represent 10 miles (to scale), which means the top will NOT... as the lines of longitude get closer together as you go further north. grid shift often affects projections involving UTM coordinates, since the metres are 'flat', and you cannot just add or subtract and get an answer canadazuuk Quote Link to comment
Kerry. Posted February 17, 2003 Share Posted February 17, 2003 A grid shift could be thought of as a less precise (simple) method of moving the grid lines (real world position) relative to the datum being used. Basically by changing datum's the grid lines move (shift), which are representative/related to the positions of fixed features as features on the ground don't move with a datum change. The relationship between datum's can be quite complex and for precise applications transformations or distortion models are used, where as for some applications/purposes grid shifts are adequate depending on the area of concern. For a single (reasonable scale) map the range might/could/can be negligible but for a whole country then the range difference is probably of some concern for critcial use. Cheers, Kerry. I never get lost everybody keeps telling me where to go Quote Link to comment
+GEO*Trailblazer 1 Posted February 17, 2003 Share Posted February 17, 2003 A little more research led me to: www.ngs.noaa.gov/PC_PROD/pc_prod.shtml WHEN ALL ELSE FAILS *GEOTRYAGAIN* http://www.msnusers.com/MissouriTrails Quote Link to comment
+ZoomZoom Posted February 17, 2003 Author Share Posted February 17, 2003 Well thank you all for these explanations which I see isn't all that simple to understand. Quess I'll have to study those two links you posted Trailblazer#1 a little bit further. Here I thought I was asking a simple question. Just goes to show you that you learn something new everyday. Once again thanks. Quote Link to comment
+apersson850 Posted February 18, 2003 Share Posted February 18, 2003 quote:Originally posted by ZoomZoom:What is a grid shift? It's what happens if you force your car into reverse gear, while it still is moving forwards. Anders Quote Link to comment
+canadazuuk Posted February 18, 2003 Share Posted February 18, 2003 the grid shift that they speak of on Vancouver Island is not going to help you solve the cache locations pythag and ed williams will Quote Link to comment
+ZoomZoom Posted February 18, 2003 Author Share Posted February 18, 2003 quote:Originally posted by canadazuuk:the grid shift that they speak of on Vancouver Island is not going to help you solve the cache locations pythag and ed williams will Why will it not help me solve it? Is there that much difference involved in a grid shift? Also who or what are pythag and ed williams? I only ask because I've never had to play with grid shift and besides that I never leave this chunk of rock just to get a waypoint on the mainland, if you know what I mean. Quote Link to comment
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