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DukeOfURL01

project waypoints as circles?

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I'm not asking for the solution here, so let's be clear about that.

 

A local puzzle is asking:

 

The cache is .11 miles from N 39 46.459 W 121.46.994

The cache is .14 miles from N 39.46.451 W 121 46.870

The cache is .28 miles from N 39.46.351 W 121.47.124

 

I know kinda what I have to do, I have to find a way to draw scale circles around these points, and then find where they intersect, and get those coordinates.

 

What I'm asking is, how do I do that?

 

thanks

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I'm not asking for the solution here, so let's be clear about that.

 

A local puzzle is asking:

 

The cache is .11 miles from N 39 46.459 W 121.46.994

The cache is .14 miles from N 39.46.451 W 121 46.870

The cache is .28 miles from N 39.46.351 W 121.47.124

 

This problem is known as "trilateration." There are several ways to do it. Finding a mapping program that allows you to draw circles is a good one. I think you can do it on gpsvisualizer.com but I'm not sure.

 

You can also do this via FizzyCalc, just iterating until all three distances are correct. I'd start by projecting a point more or less toward the middle of the points from one point the correct distance, and then move that point around until they are all right.

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I'm not asking for the solution here, so let's be clear about that.

 

A local puzzle is asking:

 

The cache is .11 miles from N 39 46.459 W 121.46.994

The cache is .14 miles from N 39.46.451 W 121 46.870

The cache is .28 miles from N 39.46.351 W 121.47.124

 

This problem is known as "trilateration." There are several ways to do it. Finding a mapping program that allows you to draw circles is a good one. I think you can do it on gpsvisualizer.com but I'm not sure.

 

You can also do this via FizzyCalc, just iterating until all three distances are correct. I'd start by projecting a point more or less toward the middle of the points from one point the correct distance, and then move that point around until they are all right.

 

Hmm, I just tried it with GPS Visualizer.com and couldn't figure out how to do it. I'll try FizzyCalc now.

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I've done similar caches with online distance calculators. I opened the online distance calculator in 3 browser tabs, one for each waypoint. Then I guess at a solution and copy-paste my guess into all 3 browser tabs to calculate the distances. Based on those distances and the desired distances, I refine my guess and repeat the process.

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Mapsource will allow you to put proximity circles around waypoints.

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Hmm, the 3 circles do not intersect. Not sure what to do now. It is GCXH7C and I know that it is probably gone anyhow, but I want to try... Any suggestions?

 

Circles.png

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Hmm, the 3 circles do not intersect. Not sure what to do now. It is GCXH7C and I know that it is probably gone anyhow, but I want to try... Any suggestions?

 

 

You may want to recheck your waypoints and proximitys. That is not how it looks in my Mapsource.

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Thanks guys (you learn something new everyday).

 

I've been using MapSource for years and never spotted the proximity option for a waypoint.

 

This could have saved me a lot of messing about with a similar cache in Spain last year.

 

Cheers

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Hmm, the 3 circles do not intersect.

It's kind of hard to see in your screenshot, but I think you mis-typed a digit in HF#6. The latitude looks like it's N39 46.659, but it should be N39 46.459.

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The last time I had a multi like this, I just punched all three waypoints into my GPSMAP 60CSx, headed between them, and then opened up the "Find waypoint" screen and walked around until the right values came up. That was using meters, not hundredths of a mile, so it was a little more accurate. (And I didn't know the distances until I found the stages of the multi, so I didn't want to come back later.) Using Map Source looks like a great way to solve the problem if one knows the points ahead of time, though.

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Hmm, the 3 circles do not intersect.

It's kind of hard to see in your screenshot, but I think you mis-typed a digit in HF#6. The latitude looks like it's N39 46.659, but it should be N39 46.459.

 

You were correct about the point where I made my typo. The new picture is not quite what I imagined though. I imagined three circles with clearly defined intersection points, but that's not what I got. I'd imagine that I'm supposed to go to that little triangular point where the circles sorta meet near the top. The only thing I can think of is to create a new waypoint and then move it there and then go to that place.

 

All this for a cache that has 3 very good cachers reporting DNFs...

 

Now how to I find the coordinates to the point where they intersect?

 

Circles2.png

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I imagined three circles with clearly defined intersection points, but that's not what I got. I'd imagine that I'm supposed to go to that little triangular point where the circles sorta meet near the top. The only thing I can think of is to create a new waypoint and then move it there and then go to that place.

Unfortunately, because the CO only used two decimal places, with rounding errors their distances could be off by as much as 50 feet for each circle. You'll basically have to guess at a point where the circles come closest to intersecting.

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2 decimal places where? I see 3 on each of the points, that is standard for geocaching points.

 

He means with the proximity distance.

In Mapsource, Click the flag icon on the tool bar and then click on the map where you think the solution is. A new waypoint will pop up in edit mode and you can then copy the coordinates.

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I solved this one using my sooper-sekrit automatic solver and the error on the final position was pretty large, meaning that the distances were not specified with enough precision. However, the actual distances from my solution, rounded to the nearest .01 mile, agree with the description.

 

This kind of frustration is common with this kind of cache; since it is easy to get the distances if you know the final location, then the hider (who doesn't really understand the inverse problem) doesn't use enough precision to make an accurate solution.

 

Similar problems occur when hiders use spherical Earth models (with unspecified radii) for distance or who try to use UTM for calculations involving more than just distance (like angles, for example).

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I solved this one using my sooper-sekrit automatic solver and the error on the final position was pretty large, meaning that the distances were not specified with enough precision. However, the actual distances from my solution, rounded to the nearest .01 mile, agree with the description.

 

This kind of frustration is common with this kind of cache; since it is easy to get the distances if you know the final location, then the hider (who doesn't really understand the inverse problem) doesn't use enough precision to make an accurate solution.

 

Similar problems occur when hiders use spherical Earth models (with unspecified radii) for distance or who try to use UTM for calculations involving more than just distance (like angles, for example).

 

They most likely got the distances by standing at GZ and using their GSP to see how far it was from the other caches. On my Garmin, this is rounded to 1/100, not 1/1000. This can be a pretty significant margin of error. Looking at Google Earth, that margin falls into a likely area but could still leave for a wide search area. At first, I thought that they had mistyped the second proximity. Using .11 instead of .14 resolves to an almost perfect solution, but a very difficult spot to get to, terrain wise.

 

If I were ever to setup a cache like this, I'd get my waypoint and then go home and figure the distances with Fizzycalc.

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If I were ever to setup a cache like this, I'd get my waypoint and then go home and figure the distances with Fizzycalc.

 

That would be the Right Way to Do It!

 

:laughing: :laughing: :laughing: :laughing: :laughing:

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If I were ever to setup a cache like this, I'd get my waypoint and then go home and figure the distances with Fizzycalc.

 

That would be the Right Way to Do It!

 

:laughing: :laughing: :laughing: :laughing: :laughing:

Hey Fizzy

 

Are you satisfied enough with the current state of FizzyCalc and dissatisfied enough with the world of Windows, that the past discussed inclusion of Datums to FizzyCalc is something that is never going to happen? I'd be happy if you offered just a sliver of hope right now. That would certainly be better than hearing it's never gonna happen. In any case I often rely on it and will continue to use it as it works perfectly as is. I guess no matter what we have, we are always looking for more.

 

Also, I once used FizzyCalc to help "crack" a somewhat similar puzzle idea which also included a bit of a different twist. I was concerned that my numbers did not line up exactly with the twist. After expressing my concern to the CO, we concluded my FizzyCalc numbers were more accurate, and the CO updated the puzzle.

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Are you satisfied enough with the current state of FizzyCalc and dissatisfied enough with the world of Windows, that the past discussed inclusion of Datums to FizzyCalc is something that is never going to happen? I'd be happy if you offered just a sliver of hope right now. That would certainly be better than hearing it's never gonna happen.

 

Actually, you know, I noticed another thread about this recently. I've now written the 3-parameter Molodensky transform and it works well, so adding another tab to FizzyCalc to do datum changes won't be too bad, assuming I can get VS2010 to rebuild the whole thing. There is a big huge database of datums out there someplace; I will probably pick a reasonably-sized subset of those to include in a drop-down.

 

I'm doing most of my geo-related development in Python now, which is nice because it runs everywhere, but is not so nice because redistribution is harder.

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If you have an Android based phone, the app GeoCache Calculator does this quite well.

 

If you stick with the MapSource route, which I have used myself many times, I usually just read the coordinates off the bottom of the screen. Select the cursor pointer tool from the toolbar up top, point the cursor in the middle of your triangle and call that an average, then read the coords and you're on your way.

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For anyone interested, I have added datum conversions to FizzyCalc. It's still beta, but it seems to work fine.

 

Get it by downloading the executable here.

 

Still free, natch. Hope people find the new functionality useful.

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The page still says version 1.01 11/5/2007, but yeah, I'm interested. Can it trilaterate 3 points instead of two?

 

Nope. I decided not to add in trilateration because it would ruin so many puzzle caches Sorry.

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It would not ruin them, indeed just the opposite, as I can find no utility that will do that, or also in reverse. It would not ruin those caches, it would enable people to finally find them. As it stands, trilaterilization is beyond most people anyhow, and still think that it would be even with the tool.

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The page still says version 1.01 11/5/2007

 

The download page now correctly identifies this new Datum Conversion enhanced release as - Current Version: 1.2.01 8/17/2012

 

And when you run the actual downloaded FizzyCalc file it also identifies itself as 1.2.01

 

There are 124 Datum selections available from the drop down menu. This will come in most handy for me when matching up WGS84 waypoints on a USGS NAD27 map. To celebrate this good news, I'll have to get serious about using this to make a more interesting placement of a hide on a county line through a Gameland. The line is well defined on my USGS NAD27 map of the area.

 

Thanks Fizzy

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