+Cache N Posted April 6, 2003 Share Posted April 6, 2003 Is the direct the GPSr give to a location based on true north or magnetic north? When get my compass out I assume the GSPr is giving me true north heading... and I need to adjust with my compass for magnetic declination... is that correct? Thanks in advance. Quote Link to comment
+nincehelser Posted April 6, 2003 Share Posted April 6, 2003 It depends on how your GPS receiver is set. One of mine defaults to true, the other to magnetic. I guess you'll have too look at the settings. George Quote Link to comment
Tahosa and Sons Posted April 7, 2003 Share Posted April 7, 2003 For clarity in your direction, your GPS should be set to Magnetic. That way your Compass and GPS can talk to each other. If you have East Declination this should help you: If west just inverse the equations. To correct for declination you want the map bearing and field bearing to be equilavent. Map bearing to magnetic bearing -> Map bearing - declination = Magnetic bearing. Magnetic bearing to map bearing -> Magnetic bearing + declination = Map bearing. Tahosa - Dweller of the Mountain Tops. Quote Link to comment
geoStrider Posted April 7, 2003 Share Posted April 7, 2003 Check your GPSr settings to see what it is set to. True vs. Magnetic is an age old debate. I prefer to set my Legend to true north. My compass has a declination adjustment to allow it to be set to true north also. If you are doing map work, this allows you to take bearings directly without having to adjust for declination. I've never been lost, but I was a might bewildered for three days once. Daniel Boone Quote Link to comment
OlyHippy Posted April 7, 2003 Share Posted April 7, 2003 Another thing worth mentioning is the declination of the region you are in. On the east coast it's about a west 10.5 degree declination. The GPS should be able to pick up the info of your area. A good little tip for doing the grid to magnetic conversions: LARS (left add, right subtract) Or west add, east subtract I hope this link works, it's a good visual: http://www.survivaliq.com/navigation/direction_par6.htm Quote Link to comment
+EScout Posted April 7, 2003 Share Posted April 7, 2003 I ditto everything Geo Strider said. Keep it all true north. When you are at a multi-cache and they give directions, change if it is magnetic. Sometimes they don't specify. On my own multi-cache, the waypoint marker gives both true and magnetic directions to the cache. Quote Link to comment
dsandbro Posted April 7, 2003 Share Posted April 7, 2003 Mag declination varies over distance, over time, and over elevation -- much more than you think. Many shareware programs exist for calculating the mag declination for any point on earth for any given date. Here's one I use: http://www.interpex.com/magfield.htm ======================================== Friends don't let Friends geocache drunk. Quote Link to comment
+MercRocks Posted April 10, 2003 Share Posted April 10, 2003 Declination for Canada Natural Resources Canada Without your brain, a map is a piece of coloured paper, a compass is a glorified magnet, and a GPS is a waterproof battery case." " FSAR " Quote Link to comment
+Waterboy Posted April 10, 2003 Share Posted April 10, 2003 quote:Originally posted by Dave54:Mag declination varies over distance, over time, and over elevation -- much more than you think. Iron ore content in the soils of Pennsylvania and some neighboring states does many weird things with magnetic declination. Quote Link to comment
dsandbro Posted April 10, 2003 Share Posted April 10, 2003 Iron ore content in the soils of Pennsylvania and some neighboring states does many weird things with magnetic declination. Local anomalies exist in many places around the world. Aviation sectionals show the larger known ones. Many more are known only to the locals. Sometimes associated with metallic ore deposits and sometimes not. One near me only a few square miles in size not only makes compasses go wacky, but GPS as well (great spot for a cache!). Navaids and AM radio signals are also intermittently affected to an altitude of about 2000 feet AGL. There are no known ore deposits underground, far from any town, and everyone is at a loss for an explanation. I like Elvis' secret underground UFO base theory myself. ======================================== Friends don't let Friends geocache drunk. Quote Link to comment
Northern-Lights Posted April 10, 2003 Share Posted April 10, 2003 I have my GPS set to magnetic north....that way my compass and GPS are set the same. I don't have to sit and figure what the difference is. Unless you get next to some iron ore.....like what we have in several places around here..you may find that it will work well for you. Earth First!!! We'll cache the other planets later!! Quote Link to comment
+Don&Betty Posted April 18, 2003 Share Posted April 18, 2003 Measure the local declination in your neighborhood yourself. Using a topo map, like are available on every geocaching.com listing, find a road that heads precisely N-S, then go there and see what heading your compass says it heads. The difference is the local declination. Quote Link to comment
+flask Posted April 18, 2003 Share Posted April 18, 2003 you're assuming that we HAVE roads that go straight. that's funny. it doesn't matter if you get to camp at one or at six. dinner is still at six. Quote Link to comment
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