Not Interested Posted March 12, 2003 Share Posted March 12, 2003 Went to find my first geocache today. The person had place his cache in oct and now here in Wisconsin it is the dead of winter. Could it be in snow? does geocaching stop or kinda slow down a bit due to snow covering caches? I had the cords marked on my map on my GPS ( Garmin ETREX VISTA ). I had a small blip on my map showing me where it said the cache should be. But my navigation told me it was 40 feet away from where the blip was and my GPS compass was totally navigaitng me the wrong way. Ive owned my GPS for about 3 months .. I thought it would be much more accurate then it is today. Most ive ever gotten was 7 feet. Mostly i get about 18-24. Any tips on using my Etrex Vista better in wooded areas and searching for caches. I dont know all the features yet. I know the GOTO and NAVIGATION. do not know what SIGHT N GO does or how to work ALTIMITER yet. ANY HELP is appreciated Quote Link to comment
TrainR Posted March 12, 2003 Share Posted March 12, 2003 May not be the problem in your case but sometimes I get a reading that shown the unit 90 degrees to one side or the other because of where I initated my track from. I have a Garmin Rino 120 so this may be not be the root of your discrepancy. Quote Link to comment
+Brian - Team A.I. Posted March 12, 2003 Share Posted March 12, 2003 Although I don't live in snow, I can venture to say that caching does slow down quite a bit in winter months, as it does here during the summer (central Arizona, home of the 120-degree summer days). If you're in a heavily wooded area, get a bearing on where you need to head in order to locate the cache, and hopefully it isn't too far in that you lose total sat sync. 40' isn't really too bad as far as accuracy is concerned. Some cachers place their caches with older, less accurate GPSr's. However, there are other factors that seem to affect location. Weird atmospheric conditions, the gov't. messing with satellites, or cachers not fully allowing their units to settle prior to locking the coords. I too am still learning how to use the Vista, and the altimeter has proven to be useful when caching in mountainous areas, if I am looking for a cache near a particular peak. All in all I've been very happy with the unit. Unlike it's competitor (Magellan SportTrak series), I love the smaller design, as it is much less cumbersome when in the boonies caching. If you want to get a better idea on where a cache might be, and your current methods aren't working, try triangulating. Take readings from at least 3 different locations around the cache site, and go from there. Odds are you will be pointing toward the same general area. Hope these help. Brian Team A.I. Quote Link to comment
+briansnat Posted March 12, 2003 Share Posted March 12, 2003 You have to remember that your GPS has a margin of error and so did the cache placers unit when he hid the cache. If yours was accurate to within 25 feet and the placers was accurate to within 25 feet whe he placed it, you could be as much as 50 feet off. The snow can make some caches harder to find. There are a lot that could be nearly impossible to find in the snow and others where the snow makes little, or no difference. Here in northern NJ we've had at least a foot and often two feet on the ground since December, but there has been a lot of geocaching activity despite the snow. I've found a few in the snow myself, including one under almost 4 feet of snow in VT (that one was pure luck though). "An appeaser is one who keeps feeding a crocodile-hoping it will eat him last" -Winston Churchill Quote Link to comment
+brad.32 Posted March 13, 2003 Share Posted March 13, 2003 quote:Originally posted by BrianSnat:You have to remember that your GPS has a margin of error and so did the cache placers unit when he hid the cache. If yours was accurate to within 25 feet and the placers was accurate to within 25 feet whe he placed it, you could be as much as 50 feet off. Exactly, but your GPS unit, and everyone else's, DOES have an accuracy of 5-10 m. There is no "if". The original question was whether there was something wrong with his GPS. No, 5-10-m error is normal. Quote Link to comment
+brad.32 Posted March 13, 2003 Share Posted March 13, 2003 This is off-topic, but I was curious about this one... The maximum error for two different GPS units is the sum of the maximum errors like Brainsnat wrote, but what is the typical error? If the cache placer and the finder go to the same place on different days, they are using a different configuration of satellites with a different PDOP, etc. I would think that makes them independent measurements with a different amount of error. Assuming a point (p) with a random error of up to e in x and y (the placer's coordinates of the cache), around the origin (the TRUE location of the cache), and a second point (f) with a random error from p (the finder's coordinates for the cache), what is the typical distance between the second point (f) and the origin (the finder's error from the cache)? For 10000, 100000, 1 million, and 10 million trials, it's about e. This shows that the random error does not compound, but only forms a relative error the same as the error of each measurement. Quote Link to comment
+Moe the Sleaze Posted March 13, 2003 Share Posted March 13, 2003 "The maximum error for two different GPS units is the sum of the maximum errors like Brainsnat wrote, but what is the typical error?" The usual method for approximating the combined error in cases like this is to RSS (Root-Sum-Square) them. That is, to calculate the total error square the individual errors, add them, and take the square root of the result. Quote Link to comment
+Renegade Knight Posted March 13, 2003 Share Posted March 13, 2003 quote:Originally posted by brad.32:The maximum error for two different GPS units is the sum of the maximum errors like Brainsnat wrote, but what is the typical error? Yeah, ok, but you know what? They invented the Monte Carlo Method for those of us who would just as well avoid the the math. After 350+ Monte Carlo Simulations my typical error is 20' or less. No worse than the typical accurcy of the person who placed the cache. Wherever you go there you are. Quote Link to comment
+brad.32 Posted March 13, 2003 Share Posted March 13, 2003 Yes, what I did is a Monte Carlo simulation, I just didn't call it that because I figured geocachers wouldn't be familiar with the term. ... so, Moe, what do you calculate for the combined error? Quote Link to comment
bobcatbeej Posted March 13, 2003 Share Posted March 13, 2003 "They invented the Monte Carlo Method for those of us who would just as well avoid the the math." So what exactly is the Monte Carlo simulation? Quote Link to comment
+brad.32 Posted March 13, 2003 Share Posted March 13, 2003 "The Monte Carlo method, as it is understood today, encompasses any technique of statistical sampling employed to approximate solutions to quantitative problems." http://www.riskglossary.com/articles/monte_carlo_method.htm It's the use of a large number of randomly generated trials to come up with estimated results. You let the computer do the work, so you don't have to do the math. Quote Link to comment
+Smitherington Posted March 13, 2003 Share Posted March 13, 2003 And I always thought that Monte Carlo was a car!! One can learn hisself a durn lot of stuff here! Quote Link to comment
Enos Shenk Posted March 15, 2003 Share Posted March 15, 2003 oh lord, and thats invented so you dont have to do the math? Id hate to see a method thats intended for math... [Episkipos Enos Shenk, KSC] [403forbidden.urbanexploration.org] Quote Link to comment
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