Need some help figuring out on a tricky math question

[+kurchian]

Would appreciate some assistance on a cache that has me vexed.

 

I have three waypoints. The cache owner has listed the distances from the three waypoints to where I will find the final.

 

So I need to enter the three pairs of coordinates and draw a circle around each WP and find the intersections of the three circles.

 

Can someone give me a nudge on what approach I can take. (I already tried using a paper map and using a compass to draw circles. But it isn't precise enough.) I am hoping someone can point me towards an application or website that I can use.

 

thank you!

[+niraD]

I've solved similar puzzles by finding an online tool that would calculate distances between waypoints. Then I opened multiple browser tabs, each viewing the online tool. I entered the given waypoints into the online tool, one waypoint per browser tab.

 

Then I took my best guess as a starting point, and copy-pasted that guess into each tab.

 

I compared the distances provided by the online tool with the specified distances, adjusted my guess, and copy-pasted the revised guess into each tab.

 

Lather rinse repeat.

[+NanCycle]

I would try Google Earth and the Ruler Tool.

[+Cardinal Red]

Would appreciate some assistance on a cache that has me vexed.

 

I have three waypoints. The cache owner has listed the distances from the three waypoints to where I will find the final.

 

So I need to enter the three pairs of coordinates and draw a circle around each WP and find the intersections of the three circles.

 

Can someone give me a nudge on what approach I can take. (I already tried using a paper map and using a compass to draw circles. But it isn't precise enough.) I am hoping someone can point me towards an application or website that I can use.

 

thank you!

 

I would like to take a look at the actual cache page. Could you provide (or email me) the GC#. Doesn't sound all that tough.

[+EScout]

There is an android app that will do this. GCC, Geocache Calculator. When you start the app, choose Coordinates, then choose Intersection Distance (Three), which let's you enter the coordinates of 3 points and distances, and calculates the intersection of the 3 circles: Trilateration. There are other good tools in this app.

Edited August 18, 2016 by EScout

[+on4bam]

Take a look at this site, it allows all kinds of stuff to be calculated/converted...

 

On Android GCC is a must have.

Edited August 18, 2016 by on4bam

[+dprovan]

Plenty of good answers, so I'll just underscore that it turns out this isn't really a "math question", it's a tool question. I mention that because it took me a while to realize that the mathematics of coordinates on the Earth's surface is nothing like anything you learned in your high school math classes. (Not that you don't need that math, too, but there's additional specialized knowledge involved that most of us will never have more than a basic understanding of.)

 

It took me longer than it should have to realize this because one of the first puzzles I did happened to involve averaging the coordinate values themselves, so that encouraged me to think such arithmetic actually made physical sense. But it doesn't.

[+Kalkendotters]

Wel it is a math question; only a bit more complicated than it looks like on first sight.

For relative small distances ( smaller than 10 miles I guess) you can work in a flat environment and use 'normal' math to calculate the points where the circles cross.

First convert the WGS coordinates to an UTM coordinate. That will give you a 'flat' surface to make the calculations. Use normal X, Y aritmetic to calculate the points.

[+dprovan]

First convert the WGS coordinates to an UTM coordinate. That will give you a 'flat' surface to make the calculations. Use normal X, Y aritmetic to calculate the points.

Isn't the specialized knowledge I mentioned just packed into the simple sounding "convert the WGS coordinates to an UTM coordinate"? I don't know about you, but I'd need a tool to do that conversion.

[+kurchian]

Some great answers here. Thank you.

 

Unfortunately I don't use an Android device so that app won't help me. I use iPhone and Mac OS. But the online Geocache Calculator may help me.

 

I'm working on getting the coordinates to the three points and will report back here as I progress.

[+Capt. Bob]

Have your tried this site? Use "#11-Intersection point of three circles".

[+kurchian]

Have your tried this site? Use "#11-Intersection point of three circles".

 

Thank you. After fooling around with fixing the link and translating it it will be useful.

[+kurchian]

Some great answers here. Thank you.

 

Unfortunately I don't use an Android device so that app won't help me. I use iPhone and Mac OS. But the online Geocache Calculator may help me.

 

I'm working on getting the coordinates to the three points and will report back here as I progress.

 

Thanks to all the help. I said I'd report bac and I am slow in doing so. Someone mentioned Geocaching Toolbox as a reference. That was my savior on this one.

[+hzoi]

I had to work a multi like this once. I knew it was in the middle somewhere, so I plugged the three waypoints into my GPSr and then just kept the "go to waypoint" menu active. It wasn't exact, but it got me what I needed.

[+Kalkendotters]

First convert the WGS coordinates to an UTM coordinate. That will give you a 'flat' surface to make the calculations. Use normal X, Y aritmetic to calculate the points.

Isn't the specialized knowledge I mentioned just packed into the simple sounding "convert the WGS coordinates to an UTM coordinate"? I don't know about you, but I'd need a tool to do that conversion.

Of course it is specialized knowledge, because you need to calculate things.

But you dont really need UTM to do the conversion, any self defined grid will work. You just create your own projection from a sphere to a flat surface and calculate your answer.

If you assume WGS is a sphere (the difference between an ellipsoid and a sphere is very small when you only have distances of 10 to 20km/miles) you can do some 'basic' math to convert it to a grid. There is no real need for specialised knowledge

 

On the other side, you can just find an app; plug in some numbers; and be amazed that the result is on the other side of the earth because you don't really understand what you are computing.

[ohgood]

Would appreciate some assistance on a cache that has me vexed.

 

I have three waypoints. The cache owner has listed the distances from the three waypoints to where I will find the final.

 

So I need to enter the three pairs of coordinates and draw a circle around each WP and find the intersections of the three circles.

 

Can someone give me a nudge on what approach I can take. (I already tried using a paper map and using a compass to draw circles. But it isn't precise enough.) I am hoping someone can point me towards an application or website that I can use.

 

thank you!

 

I used (surprise!!) the android application called locus.

 

here are the steps....

 

display three points (the points used in the picture are Geo discs) on the map that you need to find center.

 

1 use the geocaching tools plugin for locus to find the center or each pair of points. ( the blue line shows two of the points being measured )

 

 

2 draw a line from that new center point directly across to the farthest waypoint you're using. (the green line that is perpendicular to the blue line)

 

 

3 repeat for each set of points until you have plotted the center. (red lines intersecting at the blue marker)

 

 

and then if you want you can always draw circles to confirm. not really needs though, once you have what you need.

 

takes about two minutes, no internet needed, no compass, no pencils, no walking, easy peas

Edited September 15, 2016 by ohgood