How To Measure 600 Feet With Gpsr?

[+1NatureMom]

All caches have to be at least 600 feet apart from each other according to the cache saturation guidlines. My Maggie 315 does not say how many feet away I am as the pretty lil blue etrx does. SO...how do I add 600 feet to my numerical coords? example>

 

N 41. 25.100

W073.12.100

 

plus

 

600 feet

 

is what?

 

 

 

I'm math challenged and I thank you

[+ParrotRobAndCeCe]

Well, that would depend on what direction you wanted to go. Since one minute of latitude is pretty much one nautical mile, it follows that 0.1 minutes is about 600 feet. So you could add or subtract 0.1 minutes to your latitude to get:

 

N 41. 25.200

W073.12.100

 

N 41. 25.000

W073.12.100

 

Moving east/west, one degree of longitude is roughly 1nm*cos(latitude). SO at your latitude (41 25.1000N), one degree of longitude is about 45nm, which means 1nm would be 1.33 minutes of longitude, and 600 feet would be about 0.133 minutes +/-, giving:

 

N 41. 25.100

W073.11.966

 

N 41. 25.100

W073.12.233

 

These four points are only the cardinal directions, though. There are an infinite number of points that are 600 feet away from your original coordinates. Those points form a circle with your original coordinates at the center and passing through the four points I calculated.

 

All of this, of course, assumes that the earth is pretty much flat, which it essentially is over small distances :-)

[The Alethiometrists]

Here's a good website that explains the relationship between longitude and latitude and distance:

 

http://www.eomonline.com/Common/Archives/Oct95/olsen.htm

 

Roughly speaking, .001 latitude is 6 feet. Around where I am, anyway, .001 longitude is about 5 feet. Of course, the closer you get to the poles, the small the distance represented by .001 longitude.

 

To get distance apart using longitude and latitude, unless you're due north, due south, due east, or due west, you'll have to do trigonometry. For instance, if you're 300 feet east and 400 feet south, you're 500 feet from the point of beginning.

 

It's a lot of fun, for me. I've done some puzzle caches that required trig to solve them. (Did you know that in the UK, they call their benchmarks "trig points"? They look much cooler, too.) If you're doing this sort of thing, you'll want to learn how to work with a UTM grid, but you won't need that just to figure your distance from a particular point using long and lat.

[+ParrotRobAndCeCe]

Bah, it's easy. At 41°25.1'N, coordinates > 600 feet away are any Latitude La and Longitude Lo that satisfy

 

Lo^2 - 2.533Lo +1.778La^2 - 2.571La + 2.562 >= 0

 

Where La and Lo are, of course, in radians west of the prime meridian and north of the equator.

 

No problem.

[The Alethiometrists]

Moving east/west, one degree of longitude is roughly 1nm*cos(latitude).  SO at your latitude (41 25.1000N), one degree of longitude is about 45nm,

That's a good way of explaining it, but I must make one correction: You mean "minute" here, not "degree," or the Earth just got A LOT smaller.

 

Here, where I ballpark 5 feet per .001 longitude, it really works out to something like 4.85 feet. Close enough, says I.

[+ParrotRobAndCeCe]

Moving east/west, one degree of longitude is roughly 1nm*cos(latitude).  SO at your latitude (41 25.1000N), one degree of longitude is about 45nm,

That's a good way of explaining it, but I must make one correction: You mean "minute" here, not "degree," or the Earth just got A LOT smaller.

 

Here, where I ballpark 5 feet per .001 longitude, it really works out to something like 4.85 feet. Close enough, says I.

Sorry, you are, of course, right. I meant 1 MINUTE of longitude at latitude X is 1nm*cos(X). One DEGREE of longitude would be 60nm(cos(X)).

 

Thanks for the correction.

[+Munin]

Couple of thoughts I'll toss in for consideration:

 

1) If you've got a pretty good idea of where you'd like to put the cache and just want to use your GPSr out "in the field" to confirm that you're far enough away, you could use the DST (distance) display on your Maggie's Nav screens. 600 feet is 0.1136 miles. Select the waypoint for the existing cache as your goal, then flip to one of the Nav screens and make sure your current location is at least 0.12 miles away from the other cache's waypoint. If you're at least that far away, then the spot you're standing at should be okay.

 

2) If you haven't decided on a particular location yet and just want to get ideas of which areas would be "safe" to consider, one low-tech/low-math method would be to use the TopoZone link for the existing cache, select a Large map size at a scale of 1:25,000 or 1:50,000, then print the map. Steal...errrr...borrow a compass (the circle-drawing kind, not the magnetic-pointing-north kind) from one of your kids, use the scale at the bottom of the map to select a radius of approx 0.12 miles, then draw a circle using the existing cache's location as the center. Any place outside the circle should be fair game. If there's multiple caches in the area, you can use the TopoZone link on each cache's page to see where it is, mark the corresponding point on your map printout, and draw circles around each cache. Just to pick a hypothetical example near the coords you indicated, you might end up with something that looks like this:

 

[+diverhank]

My Maggie 315 does not say how many feet away I am as the pretty lil blue etrx does.

I'm confused. Why doesn't your M315 tell you how many feet you are away? It is the field that say DST. I believe it's the default but you can also customize any screen (nav, compass, etc.) to have the distance shown. I don't have the 315 but the M330...which is nearly identical and it shows me down to 0 ft .

[+carleenp]

  My Maggie 315 does not say how many feet away I am as the pretty lil blue etrx does.

I'm confused. Why doesn't your M315 tell you how many feet you are away? It is the field that say DST. I believe it's the default but you can also customize any screen (nav, compass, etc.) to have the distance shown. I don't have the 315 but the M330...which is nearly identical and it shows me down to 0 ft .

I wondered this too. I used to have a 315 and know that I once used it to see how far away I was from another cache. I think what I likely did was simply load the other cache in the gps and set it to "go to" and the arrow screen. I then found the spot for my new cache and looked at the GPS to make sure I was .1 mile (528 feet) away. The same thing as when finding a cache and the screen shows the distance away as you move toward the cache. My 315 did that fine.

Edited May 25, 2005 by carleenp

[+Logscaler and Red]

Or you could just mark the known location where you are at as a "goto" and walk away any direction until the Mag 315 says your 0.10/0.011 miles from the known location. 0.10 should be 528 feet and 0.11 shold be 580 feet.

 

Also, you might want to go the Magellens website and check to be sure you have the newest latest greatest program for the Mag 315. Then you can get down to feet like the rest of us who have one.

 

Logscaler.

[+Seth!]

Is the minimum 600 feet now? I thought it was 500 feet. Maybe it changed. At any rate, a city block is about 500 feet long. So if you can see the other geocache site (or can at least visualize where it is) and it seems like it's less than a block and a half away, you're too close!

[+mtn-man]

It is 528 feet.

 

http://www.geocaching.com/about/guidelines.aspx#sat