# What are your thoughts on obtaining accurate distances between stages of a mult-cache?

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I am setting up a multi-cache.  Each stage has a message providing  a Bearing and Distance  and a Hint to next stage instead of the coords of the next stage.

I can use several methods:

• Method 1 - I have an app that allows me to mark stage 1 waypoint and then mark stage 2 waypoint and the app provides a straight line distance and bearing from waypoint 1 to 2. The problem is that I find a substantial difference between Method 1 and Method 2.
• Method 2 - I work the site in order to get a good average waypoint coords for waypoint 1 and waypoint 2.  Then I plug those values into an online navigation tool that uses the haversine algorithm.  The calculator returns the Distance and Bearing.  The calculator also returns a satellite picture of the two waypoints and the distance line between them.  As a side note, I find the calculator's map much more accurate than just plugging the coords into Google Map.

What is the best way to accomplish this?  What method do you use?

The online navigation calculator I am using is https://www.movable-type.co.uk/scripts/latlong.html

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1 hour ago, Chipper3 said:

What is the best way to accomplish this?  What method do you use?

As the coordinates are in WGS84 standard the correct calculation method is Vincenty's formulae. Method described in your link is not correct and it is stated also on the page.

See this https://en.wikipedia.org/wiki/Vincenty's_formulae there are also links to some on-line tools using this method.

One traditional on-line distance / projection calculator is available here https://edwilliams.org/gccalc.htm

Edited by arisoft
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If the point if for Geocachers to come to about the same place as you, then I'd use the bearing and distance calculator on Geocaching Toolbox. I believe it's the best known and most used in the Geocaching community.

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What you are really doing here is to project a waypoint. Any GPS can do that, but maybe not A phone GPS. I have a few like this one listed as a puzzle. I would make sure that the distance from stage to stage is not too great. Long distance may cause error. At each stage just give them the Bearing and distance. Make sure to tell them magnetic or true. that will be important.

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5 minutes ago, Mn-treker said:

I would make sure that the distance from stage to stage is not too great. Long distance may cause error.

There should be no errors in long distances or the method is wrong or data inaccurate. Some GPS devices can not use decimal bearings making accurate projection sometimes impossible.

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Thanks to all for your input!

I used all of the  methods suggested plus google map and Google Earth Pro

Method in my Original Post - Distance = 278.770 feet Bearing = 12.87 degrees

Tool Box                                  - Distance = 278.192 feet  Bearing = 12.92 degrees

Ed Williams                             - Distance = 279.526 feet  Bearing = 12.43 degrees

Google Map                            - Distance = 278.040 feet

Google Earth Pro                   - Distance = 278.620 feet  Bearing = 12.33 degrees

iGCT Mobile Toolkit               - Distance =280.000 feet   Bearing = 12.38 degrees

For Geocaching purposes, it would seem that all these methods produce a functional result. Especially since the cacher's GPS is going to be 10-20 feet off anyway.  I am adopting the Tool Box Method  based on the input from Karst. And the fact that the drawing methods could be subject to use error in placing the line between dropped map pins.

My app for drawing a line between two points set using the apps geo location method for capturing and dropping a pin just has too much "jitter" making the coords used just have to much error and therefore the distance and bearing to be wonky. I will look for another app as that sure was handy.

Edited by Chipper3
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1 hour ago, Mn-treker said:

What you are really doing here is to project a waypoint. Any GPS can do that, but maybe not A phone GPS. I have a few like this one listed as a puzzle. I would make sure that the distance from stage to stage is not too great. Long distance may cause error. At each stage just give them the Bearing and distance. Make sure to tell them magnetic or true. that will be important.

Thank You Sir!  So now I need advice on whether a cache should be listed as multi or mystery as the projection to the next Stage waypoint must be calculated in the field.  The cacher would have to jump to a site like Tool Box to make the projection or have a 3rd party app available for use on their device.  I doubt if most could make the calculation without the help of an additional app.

Edited by Chipper3
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4 hours ago, Chipper3 said:

I am setting up a multi-cache.  Each stage has a message providing  a Bearing and Distance  and a Hint to next stage instead of the coords of the next stage.

I can use several methods:

• Method 1 - I have an app that allows me to mark stage 1 waypoint and then mark stage 2 waypoint and the app provides a straight line distance and bearing from waypoint 1 to 2. The problem is that I find a substantial difference between Method 1 and Method 2.
• Method 2 - I work the site in order to get a good average waypoint coords for waypoint 1 and waypoint 2.  Then I plug those values into an online navigation tool that uses the haversine algorithm.  The calculator returns the Distance and Bearing.  The calculator also returns a satellite picture of the two waypoints and the distance line between them.  As a side note, I find the calculator's map much more accurate than just plugging the coords into Google Map.

What is the best way to accomplish this?  What method do you use?

The online navigation calculator I am using is https://www.movable-type.co.uk/scripts/latlong.html

I go low-tech.

First stage: I get super-accurate coordinates. Multiple visits, different times of the day, then average. Do this a LOT because everything else will depend on it. Post these coordinates.

Stage two: Make the location of Stage One a waypoint on your device; either GPSr or phone. Go wander around until you find a nice place for Stage Two. Standing at Stage Two, read what your device tells you are the Bearing and Distance to get to Stage One. (ACCURATE!!!!! More waypoint averaging!!! Get this right!!!) Reverse the Bearing. That means the OTHER WAY on the compass. 90 degrees becomes 270, 23 degrees becomes 203, 300 degrees becomes 120, etcetera. THAT's what you place in Stage One as directions to Stage Two.

Stages Three & Up: Start with the coordinates for Stage Two, and repeat.

Then, the seekers have two choices:

• The seeker projects a waypoint. As stated, above most if not all GPSrs can do this, MOST phone apps can't, OR
• If the seeker has no way to project a waypoint in the field, then he or she or whatever can reverse the bearing, and use that reverse bearing and distance to get to Stage Two. That's a different kind of navigation that many people would find fun and challenging (me, anyway; maybe no one else) because you're working BACKWARDS!

These options would have to be explained in the cache writeup, of course.

I can't stress enough the importance of getting absolutely accurate coordinates for each stage, because an error on your part will be cumulative across the stages.

I use this as a suggested method in my PIA puzzle cache "Splelnig Cunots". Apologies to my foreign brethren who go look at it. You'll see.

Edited by TeamRabbitRun
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51 minutes ago, TeamRabbitRun said:

I go low-tech.

First stage: I get super-accurate coordinates. Multiple visits, different times of the day, then average. Do this a LOT because everything else will depend on it. Post these coordinates.

Stage two: Make the location of Stage One a waypoint on your device; either GPSr or phone. Go wander around until you find a nice place for Stage Two. Standing at Stage Two, read what your device tells you are the Bearing and Distance to get to Stage One. (ACCURATE!!!!! More waypoint averaging!!! Get this right!!!) Reverse the Bearing. That means the OTHER WAY on the compass. 90 degrees becomes 270, 23 degrees becomes 203, 300 degrees becomes 120, etcetera. THAT's what you place in Stage One as directions to Stage Two.

Stages Three & Up: Start with the coordinates for Stage Two, and repeat.

Then, the seekers have two choices:

• The seeker projects a waypoint. As stated, above most if not all GPSrs can do this, MOST phone apps can't, OR
• If the seeker has no way to project a waypoint in the field, then he or she or whatever can reverse the bearing, and use that reverse bearing and distance to get to Stage Two. That's a different kind of navigation that many people would find fun and challenging (me, anyway; maybe no one else) because you're working BACKWARDS!

These options would have to be explained in the cache writeup, of course.

I can't stress enough the importance of getting absolutely accurate coordinates for each stage, because an error on your part will be cumulative across the stages.

I use this as a suggested method in my PIA puzzle cache "Splelnig Cunots". Apologies to my foreign brethren who go look at it. You'll see.

I am in complete agreement on working hard to get an accurate Waypoint/Stage reading. The errors in sighted bearing or the small differences depending on the projection calculator app are insignificant compared to the large errors in coords.  Whether using coords or projection for the next Stage, I also include a clue or a hidden marker that the cacher can find once they get close.  Most are night caches so I use the birds eye reflectors (Eyes in the Trees) to get the cacher starting the next stage at the correct location.

Also, over short distances an error in sighting the bearing will not throw a cacher too far off.  Having said that, for a distance of 300 feet, an sighting error of 1 degree would cause a projected error of 5 feet. A sighting error of 5 degrees would resolve to 25 feet which would be a disaster without a clue to fine tune the location once close.  The cumulative errors would kill the joy. =)   So, those projected distances better be on the order of 150 feet.

Edited by Chipper3
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Just now, Chipper3 said:

I am in complete agreement on working hard to get an accurate Waypoint/Stage reading. The errors in sighted bearing or the small differences depending on the projection calculator app are insignificant compared to the large errors in coords.  Whether using coords or projection for the next Stage, I also include a clue or a hidden marker that the cacher can find once they get close.  Most are night caches so I use the birds eye reflectors (Eyes in the Trees) to get the cacher starting the next stage at the correct location.

Yes, and my point was all about not worrying about projection calculators in the field or forcing people to use multiple tools and apps. Might have to bump the difficulty up a notch, but that's OK; makes for a much more interesting cache experience. Gets ya favorite points, too, most likely.

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33 minutes ago, Chipper3 said:

I need advice on whether a cache should be listed as multi or mystery as the projection to the next Stage waypoint must be calculated in the field.

It is a multi cache just because it is possible to calculate on field by using a handheld GPS device.

The main difference is wether the listed waypoint has something to find or is it a bogus waypoint. If it is a bogus, then it is a mystery cache.

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53 minutes ago, Chipper3 said:

So now I need advice on whether a cache should be listed as multi or mystery as the projection to the next Stage waypoint must be calculated in the field.

The cacher would have to jump to a site like Tool Box to make the projection or have a 3rd party app available for use on their device.

I doubt if most could make the calculation without the help of an additional app.

Similar to Mn-Treker, a simple project a waypoint, one we did was a Letterbox Hybrid. Another four were multis...

We were surprised by how few people who've cached for years knew how to project waypoints with their GPSr.

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I had a cache in mind and actually started to work it out using one set of coordinates to find the first stage. Then at that stage information was provided to locate two more stages. One of those stages would have info supplying a bearing to a new stage, the second to those two would give a distance to that new stage. (Sounds worse than it would be - the first stage was in the middle of a guardrail at a  park, the second two stages were at either end of the guardrail, and the combined info would pinpoint a tree by itself). Once at the new stage (tree) a container with a new range and bearing in it would lead to yet another stage. That stage then would then have information leading to the final stage. The final stage would actually be within ten feet of one of the second stages. Basically a cacher would walk the length the park- not that big- twice.

I ended up making it a multi with only the last two stages. The guardrail was a bit too close to the road for safety and the hill between the road and the park was so steep it precluded using it for access. And the tree desired for a stage was not exactly muggle proof.

The worst part was getting that all setup so people could use the info! I had fun trying to get it all setup. Maybe use that made somewhere else.

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8 hours ago, Mn-treker said:

Any GPS can do that, but maybe not A phone GPS.

There are plenty of apps for phones that do coordinate projection, e.g Cachly and Cachetoolbox on the iPhone. Or you can go to the same online calculators as you would on your computer.

8 hours ago, Mn-treker said:

Make sure to tell them magnetic or true

Out of curiosity, if a 20 year old cache used a bearing relative to the magnetic north over a long-ish distance, would it still be findable following a projection done on GPSr?

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37 minutes ago, mustakorppi said:

Out of curiosity, if a 20 year old cache used a bearing relative to the magnetic north over a long-ish distance, would it still be findable following a projection done on GPSr?

According to the topographic maps I purchased around the turn of the century, magnetic north here was 12.8 degrees east of true north in 1999 and moving east at less than 0.01 degrees per year. It might be more of a problem in places closer to the poles, but around here I wouldn't expect it to be much of an issue and, even if it was, it'd be pretty easy to calculate back to the publication date.

Another factor of course is how well the cache is hidden. A couple of decades before I got into caching, I did a fair bit of orienteering, using topographic maps (usually 1:25000 although we occasionally had the luxury of a 1:10000 for an event), a magnetic compass for bearing and stride length to measure distance. Orienteering waypoint flags are designed to be seen from a reasonable distance, though, so it wasn't like we were looking for a nano.

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28 minutes ago, barefootjeff said:

it'd be pretty easy to calculate back to the publication date.

Just to clarify, the context of my question is a person with GPSr in the field, who finds a bearing/distance to the next waypoint. The bearing has been calculated X years ago. Can they actually get to the next waypoint using just their GPSr and the information found in the field and the cache description?

I don't know much about caching with a GPSr as I always use my phone. I know my eTrex can calculate a projection but I don't think it even shows the publication date (or hide date) of the cache. It has a selection between magnetic and true, but I don't think it has "magnetic X years ago".

Edited by mustakorppi
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Why is a GPS user concerned about magnetic north?

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5 minutes ago, GeoTrekker26 said:

Why is a GPS user concerned about magnetic north?

For one thing, some offset multi-caches assume that the seeker is using a magnetic compass, and provide bearings relative to magnetic north, not true north.

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Years ago I setup a series of puzzle caches, each with a different topic that I was interested in.  I had this story in which a geocacher launched a high altitude balloon from a certain location, and recovered flight tracker data from it after it landed.  The puzzle was a series of waypoint projections, such as "the balloon traveled 12 degrees from north for 30 minutes at 10 ft/s" or whatnot, eventually getting you to GZ of the cache.  I found that the more waypoints I put in, the less accurate the final location was.  I even had a pro puzzle creator / solver help test it with me and we gave up after not being to get repeatable accurate locations.

The point is, make sure you test this cache out with at least one person before releasing it, as waypoint projections can be tricky.

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Here's a multi-cache similar to what you are doing. In this case, it is designed to be done with a compass. Bearings and azimuths are magnetic, and distance is listed in chains. As an aid, each waypoint is described. In some cases, you cannot follow a straight line, as that would go through a building. https://www.geocaching.com/geocache/GCN4W6 I actually solved this one using Google Earth. (Both the starting and ending points are less than 3/4 kilometer from my office.) I walked the route anyhow.

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On 1/9/2022 at 9:13 PM, Isonzo Karst said:

If the point if for Geocachers to come to about the same place as you, then I'd use the bearing and distance calculator on Geocaching Toolbox. I believe it's the best known and most used in the Geocaching community.

I've had my share of problems with caches, where the "best known and most used" tool for the task at hand (like decoding a cypher) was not the one, which actually performed the task correctly. Just sayin' (maybe "Geocaching Toolbox" implements the perfect waypoint projection, I don't know).

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2 hours ago, baer2006 said:

Just sayin' (maybe "Geocaching Toolbox" implements the perfect waypoint projection, I don't know).

When I saw the results of the post by Chipper3 I was a little mixed-up because all measurements were too different.

On 1/9/2022 at 11:30 PM, Chipper3 said:

Method in my Original Post - Distance = 278.770 feet Bearing = 12.87 degrees

Tool Box                                  - Distance = 278.192 feet  Bearing = 12.92 degrees

Ed Williams                             - Distance = 279.526 feet  Bearing = 12.43 degrees

Google Map                            - Distance = 278.040 feet

Google Earth Pro                   - Distance = 278.620 feet  Bearing = 12.33 degrees

iGCT Mobile Toolkit               - Distance =280.000 feet   Bearing = 12.38 degrees

I am not using the Toolbox tool because there are several better integrated tools that also give correct results. All tools I am using, give more accurately the same results than the example above. The reason is that they are using the same algorithm. Here are results what I get when calculating distance between N0 W0, N45 W45

Tool Box         6662.472718 km                324.58994109488°

Ed Williams    6662.472718104087 km  324.5899410957089 degrees

As you see from the results, these tools are using the same algorithm. I have no clue why distances were so different in the other test. The original tool that OP was trying, gives wrong results and should be avoided when working with WGS84 coordinates.

Edited by arisoft
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21 hours ago, GeoElmo6000 said:

The point is, make sure you test this cache out with at least one person before releasing it, as waypoint projections can be tricky.

This.

However you get your offsets (distances and bearings), be sure to test them the way seekers are actually going to use them in the field. If they aren't right, then adjust them until they are.

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At this point, there is pretty much no excuse to ever use the haversine formula.  There should be no difference between distances calculated correctly unless you are giving different inputs (precision) to the different sites.   Vincenty is good to a couple of centimeters over hundreds of miles. (Not that it represents reality; it is simply a very good approximation for what it calculates).

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On 1/10/2022 at 7:01 AM, niraD said:

For one thing, some offset multi-caches assume that the seeker is using a magnetic compass, and provide bearings relative to magnetic north, not true north.

I would discourage ever using magnetic north for any multi-cache, as the error in the declination makes such projections inaccurate unless you are looking for identifiable landmarks.

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On 1/10/2022 at 12:04 AM, mustakorppi said:

Out of curiosity, if a 20 year old cache used a bearing relative to the magnetic north over a long-ish distance, would it still be findable following a projection done on GPSr?

The difference between magnetic north and true north (declination) varies quite a bit depending on where you are.  Here in Chicagoland, the difference is -4 degrees.  A moderate distance would definitely be problematic.  186 feet at a half mile here in Chicagoland.   In Los Angeles, the declination is +13 degrees. Seattle is +20.  Might not even end up in the same county.

As for your question? Yup, as long as the CO made it plain he was using magnetic north instead of true north.  In my case, I would subtract 4 degrees from his projection instructions and then do the projection on the Garmin.  We had an Army vet here who used magnetic coords on a couple of his classic old caches that needed projections.  Fortunately the distances were smaller so it wasn't too awful if you did not know how to calculate the differences.

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6 hours ago, JohnCNA said:

As for your question? Yup, as long as the CO made it plain he was using magnetic north instead of true north.  In my case, I would subtract 4 degrees from his projection instructions and then do the projection on the Garmin.  We had an Army vet here who used magnetic coords on a couple of his classic old caches that needed projections.  Fortunately the distances were smaller so it wasn't too awful if you did not know how to calculate the differences.

Is 4 degrees the difference between magnetic and true north in your area, or is it the difference between magnetic north NOW vs magnetic north when the cache was hidden?

In my area, declination is now 9 but it increases by .2 degrees per year. I personally don't think that's reasonable knowledge to expect from the cacher on a multi cache.

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3 hours ago, mustakorppi said:

Is 4 degrees the difference between magnetic and true north in your area, or is it the difference between magnetic north NOW vs magnetic north when the cache was hidden?

In my area, declination is now 9 but it increases by .2 degrees per year. I personally don't think that's reasonable knowledge to expect from the cacher on a multi cache.

That is a great point, and one that I had not considered!  I think the two caches he had hidden that used magnetic projections were close to 10 years old at the time. Fortunately the distances were within 300 feet or so.  And these were woodsy caches with ammo cans so it wasn't like hunting for micros.  In the CO's case, he had intended it as an educational series that included deciphering features on a USGS topographical map, too.

I did a quick check and in 2010 my declination was -3° instead of -4° today.  I agree that it's way too complicated to expect the average cacher to know and be able to calculate the differences.

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IMO, there are two main reasons to use magnetic north to find a cache:

• The CO wants the finder to learn how to use a compass and/or convert bearings between magnetic and true north.
• The CO is going for a higher difficulty cache.

In the first case, the declination should be included in the cache description. The latter would require the finder research the declination.

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41 minutes ago, Wet Pancake Touring Club said:

In the first case, the declination should be included in the cache description.

Why?

A magnetic compass automatically points to magnetic north; no conversion is needed. If the goal is for "the finder to learn how to use a compass", then why should the declination be included in the cache description?

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On 1/18/2022 at 9:52 AM, niraD said:

Why?

A magnetic compass automatically points to magnetic north; no conversion is needed. If the goal is for "the finder to learn how to use a compass", then why should the declination be included in the cache description?

Some us use compasses with declination offset, so they read out True degrees since topo maps are based on true.  If I go somewhere else, I need the declination for the local area.

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