Anniversary Gift? Would You Believe A Hobby?

[Elspode]

So...the wife and I are out having our anniversary dinner (a day after Samhain...we're busy witches), and she decides to tell me what she wants to get me for our anniversary. Now, this is something I had asked for a couple of years back, but she was sort of hesitant to get me one...until now.

It seems she was talking to a friend who told her all about the wonderful world of Geocaching. Simply put, Geocaching is a GPS-based version of Letterboxing, something that has been done as a sideline of hiking and orienteering for years. People fill a suitable container (Tupperware works very well) with a logbook, pencil/pen, and various and sundry items of their choosing, then post the coordinates on www.geocaching.com . Other people find the coordinates, d/l them into their GPS's, and strike out in search of the various caches.

When you find them, you take something out and put something back in, write on the logbook, then log your find online.

So, my gift was a Garmin ETrex Legend GPS, made right here in the KC area. Small and amazingly useful, I am in total love with this device, the Geocaching pasttime (did our first two yesterday), and, of course, the great woman who put all this together for us to do as a couple.

http://www.garmin.com/products/etrexLegend/

Now...anyone got any Garmin Mapsource Disks hanging around? These buggers are expensive as hell, but really crucial to getting the most out of this GPS unit.

[xoxoxoBruce]

Congrats, now you know where you're at.

[Beestie]

I heard about that years ago and thought it was the coolest thing.

But, when I first heard about it, GPS was not involved so there was actually a challenge to find it - geographic "pirate's map" clues were used instead of GPS coordinates.

Not to dampen anyone's enthusiasm but it seems that the goody boxes are almost too easy to find now with the GPS. But it still sounds like a cool adventure and one me and the wife could get into.

[Elspode]

The GPS gets you to the site, but you still have to use clues provided on the site, and good old-fashioned "pirate's treasure hunting" skills to actually locate the hidden cache. Stuff that has been concealed in a complex terrain is damn hard to find. Curiously, a GPS doesn't go to zero when you are on top of a location...it gets kind of weird, and shifts around, due to the inherent accuracy limitations, the amount of arboreal cover blocking the signal, and other factors.

The third cache we looked for on Sunday was not found by us, because I figured that it would be easy, and did not print out the clues and bring them along...

[xoxoxoBruce]

Is the position they give you accurate? If you can't get a right on the spot reading, could you take a few readings and triangulate the box?

[Elspode]

If you are able to receive a WAAS-enabled satellite (or even both of them which are so equipped), you can get accuracy down to 3 meters, which I can get under good conditions. Is that accurate enough?

Real world use, without a lot tree cover, tall buildings or hills around you is 10-20 meters...still pretty damn good. Higher-end units apparently do 'averaging' automatically, and give you a distilled location based on multiple readings. The essential function of GPS *is* triangulation, anyway...triangulation with the GPS satellites as the basis. You need three satellites minimum to give you your location in three dimensions...long, lat and elevation. In fact, you don't get a reading at all on my unit without three satellites. The more satellites you receive well, the higher your accuracy. I've read tales of other users getting a zero error reading if they put the unit down and leave it for a bit.

I have a freeware program I downloaded called USA Photomap that lets you upload your GPS tracks and superimpose them over the Terraserver aerial photos/topos of whatever area you designate. I've got most of the KC metro area downloaded and in the program now, and it is spot on. I'll .jpg one of the tracks later on and upload it for you to look at.

This is cool, cool shit, man.

[perth]

Originally posted by Elspode
I have a freeware program I downloaded called USA Photomap that lets you upload your GPS tracks and superimpose them over the Terraserver aerial photos/topos of whatever area you designate. I've got most of the KC metro area downloaded and in the program now, and it is spot on. I'll .jpg one of the tracks later on and upload it for you to look at.

Link, man, Link! I'm too lazy to google it.

[OnyxCougar]

One of my ex husbands (the one that moved to Virginia recently) got into Geocaching about a year ago.


I bought a GPS unit for my car (my speedometer doesn't work), and had forgotten about Geocaching until I read your post, and I think we might try that, once I get a new starter for the Neon. *sigh*

[Elspode]

http://jdmcox.com/

[xoxoxoBruce]

[quote]Originally posted by Elspode
If you are able to receive a WAAS-enabled satellite (or even both of them which are so equipped), you can get accuracy down to 3 meters, which I can get under good conditions. Is that accurate enough?[quote]

I don't know. Is it?

Real world use, without a lot tree cover, tall buildings or hills around you is 10-20 meters...still pretty damn good. Higher-end units apparently do 'averaging' automatically, and give you a distilled location based on multiple readings. The essential function of GPS *is* triangulation, ..snip

Let me clarify. If they give you an "exact" location, but you can only come close because of interference, can you take several readings around the target and triangulate the exact location. Or do you have to search a 40 meter or so diameter area for the goodie box? Hope that's a more gooder explanation.

[Elspode]

Ah...I get it now. Duh.

The inherent accuracy of the GPS is more than sufficient to get you into rather close visual proximity of the object. Then, you have to find the likeliest place for it to be hidden. More often than not, there are the aforementioned "pirates treasure" type clues included. Sometimes these are encrypted so you can try to find it first without the extra info, then decrypt the message (the key is given on the same page if you with to print it out and take it with you) and hopefully have all the clues you need.

[xoxoxoBruce]

Ah so. I read the miners that were rescued in PA last year by drilling into the pocket where they were trapped, were pinpointed with some kind of super GPS. Military/CIA stuff, good to a foot or so. Of course hitting them dead on still involves shit luck but they did locate the pocket shown on the charts.

[perth]

I'm too lazy to go hunting for the info, but I believe its somewhere on geocaching.com. Supposedly there is an artificial margin of error for civilian use of GPS, reduced in 1996(?) from like 20 feet to 6 feet. So I imagine military application of GPS tech is much more accurate.

[Elspode]

Perth is correct. Civilian GPS has a built-in margin of error, but it is a silly small amount. Civilian units are accurate to about 12 feet, I think, and military stuff is gnats-ass on the money, with an margin of error of mere inches.

[russotto]

The artificial margin of error (Selective Availability) for civilian GPS was discontinued in May 2000. Civilian units still only have access to the C/A code, which is nominally accurate to 15 feet. The military gets the P(Y) code as well, which is nominally accurate to 1 foot. Fancy civilian units can still use the L2 signal to correct for ionospheric interference; this gets you more accuracy, as do the better antennas on the fancy units. Wide area differential GPS (which is available on really cheap units) can also get you down to the 1 foot range if you can get the signals. Survey-type differential GPS (still civilian) can get you to the sub-cm range, but not in real time, and it requires two units, one with an accurately-known position.