Author Topic: Determining coordinates based on distances from other caches  (Read 2089 times)

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BlackRose67

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Determining coordinates based on distances from other caches
« on: September 14, 2012, 22:38:42 »
This is a new one for me...determining a GZ by quadrangulation based on distance (in meters) from other caches in the vicinity.

A few weeks ago I was in the Monaghan Forest seeking birdies and rats, etc.

When I got home, I discovered that there was a mystery cache based on some of the birdies I had found that day (Lost Birdie - GC1A7FQ).
I probably walked right by the area as I was heading for one of the last birdies.

By using the proximity circle function on my smartphone, I have an idea of the general area where the cache is located, as there is a noticeable gap in the circles.

Lost Birdie is the first cache I have come across where the location of the GZ is specified as being X metres from 4 different caches.

I tried using BaseCamp to measure the distances and set a waypoint that I move around based on the distances, but I was not making any noticeable progress with that method.

I have the GSAK demo installed, but I can't see how I could use it to determine where the GZ is.

I could probably locate the cache by using the hint and photos on the cache page and wander around for a while, but I'd prefer to figure out the GZ based on the info provided in the cache page.

What's the preferred way to determine a GZ for a puzzle cache such as this one?

Xira

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Re: Determining coordinates based on distances from other caches
« Reply #1 on: September 14, 2012, 23:41:47 »
Welcome to geometry on your GPS. Proximity circles are just the beginning.

If the proximity circle function on your smartphone is accurate, then the four circles will intersect at one particular point. That's where the Lost Birdie is.

BaseCamp will also work. Do the following:
-- Use the waypoint tool to create a waypoint for each birdie.
-- For each birdie, select, then choose Edit:Properties (or right click in the list view)
-- Set the proximity field to the appropriate value, e.g. 189m

A circle will appear around each one. You will see them intersect at one particular point. Use the waypoint tool to create a waypoint there.

Note that the proximity circles display as ellipses rather than circles. But it all works just fine.

If, instead of creating the waypoints directly, you loaded a GPX file with the birdies, they will appear as geocaches, which don't have the same sorts of properties. Select the waypoint tool, then in map area, click on each one. It will duplicate the geocache as a waypoint. Then you can access the properties.

Mapsource is the predecessor to BaseCamp. It's similar, and for this sort of thing, actually nicier to use. I prefer it over BaseCamp, which I rarely use. If someone has a better way to use BaseCamp for this, please share it.

GSAK will not help you with this at all. Use it to record the final for Lost Birdie after you determine what it is.

CocaColaCacher

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Re: Determining coordinates based on distances from other caches
« Reply #2 on: September 15, 2012, 07:19:21 »
I did that cache in the field the hard way (but it wasn't too bad).  I just walked around with my GPSr looking at the other caches until I was the proper distance from each and I found the cache.  It only took about 10 min.  I'm sure there is a better way though.

BlackRose67

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Re: Determining coordinates based on distances from other caches
« Reply #3 on: September 15, 2012, 08:55:09 »
Thank You Xira!!!!

I think you told me about the proximity circle option in BaseCamp/MapSource at the last Meet n Eat....and I forgot all about it :'(

I do have a copy of MapSource installed as well.

I created the proximity circles for the 4 caches like you said and I came up with a location that was in that gap in the proximity circles on my phone app.

That was much easier than the way I had been approaching it.

portera

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Re: Determining coordinates based on distances from other caches
« Reply #4 on: September 15, 2012, 10:38:12 »
And if you don't have Mapsource (which I vastly prefer to BaseCamp) you can get it by following the instruction at this link.

http://forums.gpsreview.net/viewtopic.php?t=4802

GreyingJay

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Re: Determining coordinates based on distances from other caches
« Reply #5 on: September 17, 2012, 08:38:26 »
Not exactly related, but this reminds me of the time I found a binthair cache by a similar method of deduction -- looking at caches nearby and deducing the coordinates. Sssh, don't tell anyone :)


Starkiller

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Re: Determining coordinates based on distances from other caches
« Reply #6 on: September 17, 2012, 12:16:06 »
And if you don't have Mapsource (which I vastly prefer to BaseCamp) you can get it by following the instruction at this link.

http://forums.gpsreview.net/viewtopic.php?t=4802


I still prefer mapsource... but Basecamp has been vastly improved since its earlier versions.

elyob

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Re: Determining coordinates based on distances from other caches
« Reply #7 on: September 17, 2012, 12:27:27 »
Not exactly related, but this reminds me of the time I found a binthair cache by a similar method of deduction -- looking at caches nearby and deducing the coordinates. Sssh, don't tell anyone :)
I won't tell.  I love that method.