Joined: April 2008
||Posted: April 28 2010,7:03 pm
Sharing some stuff written by a Northern Virgina geocaher
Original NoVAGO Thread
Geocaching "enlightenment" Chapter 1 "Coordinates"
|I’ve “labored” over this for the past couple of months…not knowing just how to present it, how to get it in front of the cachers who might “benefit” the most from it (I haven't yet figured out how to reach non-NoVAGO members), how to not insult any (ahem) of the older more experienced cachers among us :wink: , or even if I need to present it at all. Just what the heck am I talking about? :smt102|
Well, over the past several months I (and a few not so vocal others) have noticed more and more caches with “loose” coordinates; really skimpy cache pages; a lack of cache page attributes and/or child waypoints; some really “wild” D & T ratings; and most troubling of all...what I suspect (in a few cases) is a failure to adhere to local area published Park Guidelines as they pertain to placing a geocache. I’m no expert, but my lips hurt from biting them : ...so I’m going to write a book :smt024 . A book released here in the forums, one chapter at a time. There’s no set schedule, nor is there any order of precedence, but I will try to put out a new chapter every week or two. Then, when the book is complete...I’ll assemble all the chapters, and post it here in its entirety as a “Sticky”...where anyone can go for reference. So far I’ve written 6 chapters: Coordinates; Location; Containers; Cache Pages; Permission; Maintenance...and there may be a couple more. I invite you to comment, or make additions, even debate...as I said - I’m no expert, but please stay on topic for the subject matter contained in each chapter as it’s published...and I really don’t want this to slip into an exchange about container sizes, cache types, or choices of locations - they are all fine, and “Everyone plays this game their own way”.
I don’t have a title for the “book”...maybe it will be “Take Pride in your Hide”, or “A Caching Primer”, or “Caching Basics 101”…we’ll see. With that said, for good or ill…here is:
Chapter 1 “Coordinates”
In the geocaching world they are that alpha/numeric string of 2 letters and 15 numbers that pinpoint (within 15 feet or so) your exact position on the face of the Earth. They are written in Lat/Lon Hddd mm.mmm format (Example: N38 35.238 W077 22.051 that’s North 38 Degrees 35 point 238 minutes and West 077 degrees 22 point 051 minutes. Again, in the geocaching world they are generally accepted as being applied to WGS84 (World Geodetic System) map datum. That puts everybody on the same sheet of music so they can find a cache, where they parked their vehicle, or the way back home.
1. Accurate coordinates depend on the number of satellites in view, the current satellite configuration, atmospheric interference, and good reception. Reception is not affected by weather, darkness, or cloud cover. Reception is affected by things that block your GPS receiver from receiving a strong signal from the satellites: tall city buildings, narrow canyons, heavy (green) leaf canopy, your body, etc.. GPS receiver manufacturers use EPE (Estimated Position Error displays) to give you an approximation of the strength/accuracy of the satellite signals being received by your handheld device - 10 feet, 15 feet, 30 feet, etc.. The lower the EPE, the better the supposed accuracy (generally).
2. Always try to mark the coordinates for your chosen location with the lowest EPE possible. It’s no guarantee they are completely accurate, but it betters the odds.
3. Check the satellite page on your GPS receiver to note the configuration of satellites, see the concentric rings on that page? A “scattered” configuration with satellites overhead (centered), at 45 degrees (middle ring), and on the horizon (outer most ring) will usually give the greatest accuracy. If your satellite page indicates the satellites are in a more-or-less straight line...reception will normally be poor, and your EPE will be higher.
4. Averaging your waypoint (cache location) is not always reliable, if you have poor reception/accuracy you’ll just be averaging bad coordinates (garbage in, garbage out). The most reliable way to average coordinates is to visit the location on different days, and at different times. (Those geosynchronous satellites move - circumnavigating the Earth once every 12 hours). Mark the new coordinates each time you visit, and then average all those that you’ve recorded.
5. One way to assess accuracy of your averaged coordinates is to select your marked waypoint, then walk 100/200 feet away from that waypoint (i.e. your cache coordinates), do a GoTo, and (moving steadily) follow your compass arrow back to the marked waypoint location...all the while watching the distance to destination as it counts down on your approach that marked location. Repeat from all 4 Cardinal Directions. If your distance to destination consistently counts down to within 5 to 15 feet during each of those 4 approaches to your marked waypoint...you can be reasonably sure that you have the best coordinates possible.
What do you think?
Dave - Happy Trails!
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