Are Some Gps Units More Accurate?

[+Zac Pac]

I am very new to Geocaching. I have a Garmin Etrex (yellow) that is about 4 years old. I have been at least 80 feet off at every cache. Is this typical? Am I using my GPS incorrectly? Or are some GPS units more accurate than others? My family is hooked on Geocaching. Do I need to upgrade?

[+Sputnik 57]

80 feet off is a lot. To me it suggests that you my have your datum set wrong. Make sure that the datum set on your Yellow is WGS84, and not NAD 27. There should be instructions for this in the manual. If you can't find your manual, it is available online from www.garmin.com.

 

Another suggestion is to make sure you are getting a good satellite lock. As I recall, the Yellow has a patch antenna that works best when the unit is held flat, screen pointing toward the sky, with an unobstructed view (don't hover over it).

 

It is often said that the Yellow Etrex has found more caches than any other unit. It should work just fine.

 

Welcome the the recreational activity/sport/hobby/addiction!

[Dale_Lynn]

Accuracy can be deceiving..... Say for instance if your GPS has a 25ft error factor that puts you north of the actual location and the cache pacer has a 25 ft. error factor south of exact location then the cache coordinates can be 50ft off actual "spot"... That said, yes you may have a error factor of 80ft off on older unit (is firmware upgradeable) . Also are you sure the "coordinate system" the GPS is using is the same as the "coordinate system" that the way point you are searching for is the same type. Only once have I actually ever been "0-ft." from a cache and has it been accurate.... Usually when GPS says I am with in 50 ft. of cache I figure I am in visual search mode, but yes I do try to get as close as GPS unit indicates to exact location.

 

Dale

[+Zac Pac]

Make sure that the datum set on your Yellow is WGS84, and not NAD 27.

OK. My map datum was set to ND27. I changed it to WGS 84. My coordinates are set to hddd.mm.mmm. Do I need to change any of the other settings? My "Units" is set to "Statute." "North Ref." is set to "Magnetic." "Variance" is set to "11 degress W"

[Neo_Geo]

"North Ref." is set to "Magnetic." "Variance" is set to "11 degress W"

Unless you're working with maps that are oriented with Magnetic North (flying, boating, etc.), then True North would be a better setting for you. This has probably not been a factor in your accuracy issues of the past, but it could cause a problem for you in the future (waypoint projection).

[+Rubberhead]

Make sure that the datum set on your Yellow is WGS84, and not NAD 27.

OK. My map datum was set to ND27. I changed it to WGS 84. My coordinates are set to hddd.mm.mmm. Do I need to change any of the other settings? My "Units" is set to "Statute." "North Ref." is set to "Magnetic." "Variance" is set to "11 degress W"

Changing datums should fix your problem.

 

I agree with Neo Geo, go with True North.

[+Zac Pac]

I made all of the changes recommended above and went out and walked directly to two caches. Thanks so much for your help!!!!

[+IVxIV]

Why would you guys recommend choosing True North over Magnetic North?

 

In my case, once I get near a cache site I will stop and let the GPSr settle down and give me a distance/direction reading for my target. Using Magnetic north option I can take the direction degree # from the GPSr & head that way using my compass.

 

What advantage does "true north" give you especially in the field?

[+Z_Statman]

I would also like to know the answer to IVxIV's question.

 

My Meridian Color has been set to magnetic and I seem to always go past the cache site then circle around to the hide. I plan to change to True and see what happens and will post another response later this week.

 

Still, very interested in the answer.

[indybill]

Why would you guys recommend choosing True North over Magnetic North?

 

In my case, once I get near a cache site I will stop and let the GPSr settle down and give me a distance/direction reading for my target. Using Magnetic north option I can take the direction degree # from the GPSr & head that way using my compass.

 

What advantage does "true north" give you especially in the field?

True North is how most maps are drawn. You can adjust the needle on many compasses to account for local magnetic declination and point to true north also.

Makes it less confusing if you don't have to remember to add/subtract the declination to get a true heading.

 

Regards,

Indybill

[+IVxIV]

..Makes it less confusing if you don't have to remember to add/subtract the declination to get a true heading

 

Umm, sorry but I don't understand how "that" is less confusing.

 

For example if my GPSr claims the target is at a bearing of 245 degrees "magnetic", I don't need to do any math,, I point the compass & go exactly at a heading of 245 degrees. No need to adjust for declination at all.

[IceKnight (aka VectorJoe)]

..Makes it less confusing if you don't have to remember to add/subtract the declination to get a true heading

 

Umm, sorry but I don't understand how "that" is less confusing.

 

For example if my GPSr claims the target is at a bearing of 245 degrees "magnetic", I don't need to do any math,, I point the compass & go exactly at a heading of 245 degrees. No need to adjust for declination at all.

I guess it would depend on if you are using a map.

 

I have never used a paper map, only the one on my gps, so aligning with magnetic north would be the way to set if I want to use a compass as well.

 

If you are going to specifically use a paper map like IndyBill, then aligning with true north would work (if the map is aligned with true north.

[+Muddy Buddies]

My Meridian Color has been set to magnetic and I seem to always go past the cache site then circle around to the hide. I plan to change to True and see what happens and will post another response later this week.

I have heard that the "circling" that you mention is common with the Magellan series of GPSr's. I have a Magellan Gold, and it happens to me also. It doesn't seem to matter whether the North reference is true or magnetic. It takes the Magellan several minutes to average into the proper location. I have found that by stopping about 100' to 150' from the cache and noting the direction, that I can hone in much quicker.

[+Z_Statman]

Agree, Muddy Buddies, but I "really want to get to the find." Even so, I force patience [sometimes].

 

So you have worked with both TN & MN and get the same circling?

[indybill]

..Makes it less confusing if you don't have to remember to add/subtract the declination to get a true heading

 

Umm, sorry but I don't understand how "that" is less confusing.

 

For example if my GPSr claims the target is at a bearing of 245 degrees "magnetic", I don't need to do any math,, I point the compass & go exactly at a heading of 245 degrees. No need to adjust for declination at all.

Please reread my whole post (it's only 4 lines ). If you can adjust your compass to account for magnetic declination then set your gpsr to read true north; all will be in sync with your map source whether its mapquest, paper or whatever.

 

If you cannot adjust your compass for magnetic delclination and do not use any other map source than your gpsr then setting your gpsr to read magnetic north would work fine as it and your compass would match.

 

It's when you try to mix the two amongst map, gpsr, and compass that things can get confusing and errors can be made.

 

Regards,

Indybill

[+embra]

I have heard that the "circling" that you mention is common with the Magellan series of GPSr's. I have a Magellan Gold, and it happens to me also. It doesn't seem to matter whether the North reference is true or magnetic. It takes the Magellan several minutes to average into the proper location. I have found that by stopping about 100' to 150' from the cache and noting the direction, that I can hone in much quicker.

As an alternative to waiting a minute or so for things to settle down, Magellan users have found turning the units off and back on an effective way to clear the moving average data out...of course, you may have to reset a single waypoint GOTO.

 

While I can't say that I've checked TN and MN against each other on this, I can't think of any reason why that setting would make any difference.

[+Logscaler and Red]

Whenever this topic pops up, I refer to THIS cache.

 

Also, as for doing the buzzard trick with the maggies - turning slow circles down to the cache location - I just set the proximity alarm to 100 feet and when it starts beeping, I slow down the walking and start looking for the most likely pile of sticks, rocks, chunks, stumps, hollow log, ivy patch, etc to where the cache might be in the general direction we where walking.

 

As for the TN vs MN debate, if people don't know the reason why, it only takes one night in the outdoors after missing the trailhead on the map to learn that MN is better. The S&R people will explain it in the next day or so.

 

Logscaler.

[indybill]

Here's some info on the TN/MN subject from USGS:

http://rockyweb.cr.usgs.gov/public/outreach/gps/compass_gps_north.html

 

http://erg.usgs.gov/isb/pubs/factsheets/fs03501.html

Edited February 18, 2005 by indybill

[+Zac Pac]

Whenever this topic pops up, I refer to THIS cache.

 

Also, as for doing the buzzard trick with the maggies - turning slow circles down to the cache location - I just set the proximity alarm to 100 feet and when it starts beeping, I slow down the walking and start looking for the most likely pile of sticks, rocks, chunks, stumps, hollow log, ivy patch, etc to where the cache might be in the general direction we where walking.

 

As for the TN vs MN debate, if people don't know the reason why, it only takes one night in the outdoors after missing the trailhead on the map to learn that MN is better. The S&R people will explain it in the next day or so.

 

Logscaler.

Did I miss something? Are you including plane tickets and a rental car with that link? If not, it doesn't do me a whole lot of good sitting in Pennsylvania.

[+vofsar]

How would most of you folks out there set your GPS altimeter? I have a Garmin Etrex Vista that has auto or manual altimeter settings. When benchmarking/geocaching my partner and I both use our Vistas, we are always the same with the coords, but one of us is always off on the elevation...the problem is which one of us? I set mine using TOPO! software maps. TOPO! software is not accurate enough, I tried using the contour lines, but they are off. I thought of going to our local airport and checking the elevation there. Any ideas?

 

Thanks, Steve.

[indybill]

You might try looking for an established benchmark near your home. Do a google search for 'elevation benchmarks (your city)'. That's how I found some near me.

 

Regards,

Indybill

[+Zac Pac]

Thanks for the clarification Indy-That makes sense, I am new to all of this, so i am just trying to figure it all out!!!

 

Jarrod

[+Logscaler and Red]

The point I was trying to get across by pointing out that cache is that I myself think it is a good cache idea for any location.

 

This way, all the cachers in that area can compare their different gpsr units to see how they matchup with the other local units And you might then find and fix a problem like being on the wrong datum.

 

Just look for a local county or state or city control point that is easy to access but kinda out of the local mainstream of traffic.

 

And if you wanna fly out here and find ours, fine, but I think you would be better off making your own.

 

Logscaler.

[+Night Stalker]

I have used both the Magellan SporTrak Pro and now a 60CS. Each one seems to have its own way of doing things. One is not better then the other. I found that to eliminate the circling all I needed to do was walk slowly as I got closer to the cache. If you do this it seems to catch up. With the 60CS it doesn't seem to have quite as good a signal under heavy tree cover so I end up doing the circling thing with it. When I cached with Renegade Knight I used my Magellan and he used a GPS V. We were always within 6' of each other when we zeroed out. Sometimes the Magellan was closer and sometime the Garmin was closer. Neither one was far enough off to prevent the user from finding the cache.

 

[+Renegade Knight]

True North, Magentic North

 

It's sixes. I don't use a Compas in conjunction with my GPS to find a cache. I walk to within about 6-10' and just start looking.

 

Now when it comes to reading a map then it becomes important. Most maps are oriented towards True North (more or less) and you need to either account for the declanation or adjust for it directly. I normaly always adjust the maps to fit the lay of the land without thinking. But I'm used to big sky country and you can see everything.

 

Also if you mark your car and the compass on your GPS is pointing at that... Which version of north doesn't really matter as it's Car North (so to speak) you are working with.

 

The only north that has ever messed me up is Plan North. This was the North that an Architect invented to make the building line up on his plan sheets. He wanted the engineers to use it as well. Whenever he was talking about west or east side of the building it would actually be the north or south side and it took a while to even figure out what he was talking about. Once we finally figured out what the heck he did...We didn't use plan north and ignored his request and told him to use True North (Grid north actually).

 

Now I'm going to have to play with my GPS and see what it's set on and see if swaping to the other version of North changes anything that I can tell.

Edited February 19, 2005 by Renegade Knight