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Written by thenomad
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Sunday, 20 January 2008 08:12 |
How to get good, accurate coordinates
IntroductionSnapping a waypoint with good accuracy is essential to hiding a geocache. There is nothing more frustrating than searching for a geocache and not finding it, only to discover that the posted coordinates were really inaccurate. One of my finds this past week was nearly 80 feet away from the posted coordinates. 80 feet is a long way away - especially when you have a GPS receiver with WAAS (Wide Area Augmentation System).
The focus of this article is to provide hints and tips on getting good coordinates. I mostly have experience with the Garmin GPS-V, but I'll also provide helpful information on the Magellan and Lowrance as well. This article will not be used as fodder for a "which GPSr is better" debate - I'll leave that to the forums.
Unobstructed viewThe first step to getting a good set of coordinates is to get your receiver's antenna an unobstructed view of the sky. Many times, particularly when hiding a cache in a dense forest, this isn't completely possible.
I've known cache hiders that will climb a tree and poke the GPS receiver out of the canopy to get a good view of the sky. Others have used poles to move branches out of the way to get a good reading. Another hider I met took a pool leaf rake on an extension pole out with him, and put the GPSr in the net part. He was able to elevate the GPSr above the obstruction and get a good reading. I can only imagine someone's surprise at seeing him walk through a forest with a pool leaf rake though.
Some GPS receivers either have detachable antennas, or can accept external antennas. The Garmin GPS-V has a detachable antenna, and the 60C allows you to attach an external antenna. With these units, you can purchase an antenna (such as the GA26C) on a long wire (8') and poke the antenna part out above the obstruction. You can also buy additional 8' extension cables if you're so inclined.
Sometimes, it may be necessary to step 2 or 3 feet away from the cache to get a good lock on the satellites. It is generally better to have really accurate coordinates 3 feet away from the cache, than really bad coordinates on top of the cache. Case in point would be a hide at the base of a palmetto. There is no really good way to hold a GPSr above the palmetto (unless you bring a leaf rake), but setting the GPSr on the ground 3' from the cache will likely provide very accurate coordinates.
[size=16][b]Averaging your coordinates[/b][/size]
The next step to getting a good set of coordinates is to use your unit's averaging function. This takes time. Yes, that's right, time. Nothing good can come of tossing a piece of tupperware in the bushes and snapping a quick waypoint. You are assured to have bad coordinates.
To get good coordinates, it requires about five minutes of averaging. This will seem like an eternity, but the results are well worth the wait. The five minutes you invest here can literally save hours of other peoples' time.
Garmin units (specifically the GPS-III, GPS-V, and 60C, and possibly others as well) have an averaging function that you must manually invoke through a menu. Magellan units (specifically the Sportrak units and possibly others) have an automatic averaging function that kicks in when the unit is still.
To average your waypoint on Garmin units, you begin by placing the unit on the spot (on the cache or the object the cache is in), and holding down the Mark button (note - button names and menus may differ between units so please consult your users' guide). When the new waypoint screen appears, hit Menu, and choose Average Location. Leave the unit alone for five minutes. After the five minutes have elapsed, you can use the menu to save the new waypoint.
For Magellan units, simply place your GPSr at the spot (on the cache or the object the cache is hidden in) and leave it alone for five or more minutes. After the time has elapsed, return to the GPSr and snap your waypoint.
The Lowrance iFinder Pro also provides the ability to average your waypoint. This feature is called "Average Position". Please refer to your manual to see how to capture a waypoint using "Average Position".
What if your unit doesn't have waypoint averaging (e.g. Garmin eTrex, Garmin Geko, Lowrance iFinder Plus)? Well, no matter what, sitting the unit down and leaving it for 5 minutes can only improve it's accuracy. It will increase the opportunity to lock onto more satellites. For these units, simply leave the GPSr on top of the cache for five or so minutes. Then, snap the waypoint.
[size=16][b]Test your coordinates[/b][/size]
The next step is to test your coordinates. You can do this by walking about 200 feet from the cache, and then finding the waypoint. It should take you to within 10' of the cache if everything was done properly. If it doesn't, then you need to start the averaging all over, or consider trying to capture the waypoint at a different time of day. When I perform this step, I turn off my GPSr, walk 200' or so away from the cache, and turn on the GPSr. Then, I use find nearest waypoint and navigate back to the cache.
When placing a cache that has heavy tree cover along the route to the cache, it's often useful to go back to the parking area, and navigate to the cache from there. This will tell you whether finders will lose satellite coverage along the way, and how long the coverage is lost. On a few caches we did in NC, the tree cover was non-existent for stretches as long as .1 of a mile! This information would be good to share on your cache page.
[size=16][b]GPSr accuracy[/b][/size]
On nearly every handheld unit with WAAS I've seen, there is a display of the GPSr's accuracy. Understanding the accuracy reading is important to finding a cache as well as placing it. Remember that it is only an estimate by the unit of it's own accuracy. Think about that for a second. The unit is estimating it's own accuracy. Pretty much, that's like asking an interview candidate who the best person for the job is. In most cases, it's optimistic at best.
Most people assume that if the accuracy shows 12' of accuracy and they are zero'd out, then the cache must be somewhere within a 12' circle. Many many times, this is simply not true. Why? Because for one, many cache hiders don't average their waypoints. Secondly, each manufacturer has a different level of optimism about the accuracy of the unit with respect to the number of satellites acquired and the signal strength.
But, the information is useful anyway. In general, a higher number means that the GPSr is having difficulty locking onto the satellites. A lower number generally means it has a lock on more satellites. When you're hiding a cache, make note of the accuracy reading when you finally save the waypoint - this is good information for your cache page.
[size=16][b]Conclusion[/b][/size]
Nobody wants to go searching for a cache in the wrong spot. That wastes hours of time better spent doing other things. On my North Carolina trip, my wife and I figured that we spent over four hours looking for caches that had bad coordinates. Let's not do that to our fellow cachers. The five minutes you spend getting really accurate coordinates can literally save hours of wasted time.
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Last Updated on Tuesday, 22 January 2008 10:56 |
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