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ByronForestPreserve

Map and compass caching (UTM)

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Hi all--

 

I'm going to be working with Boy Scouts on the newer Geocaching badge. One of the requirements is to learn how to use a map and compass to cache. So we're getting into UTM territory here...this is going to be interesting. :) Do any of you regularly use a topo map & compass when caching? How close did it really get you? The REI site explains that the last step in finding a cache using UTM and a map/compass is to turn on your GPSr and use the pointer to "fine tune" your search. <_<

 

So I'm wrapping my head around the practical aspects--let's say I get the UTM waypoint conversion, then mark it on my topo using the grid overlay. Great. But then when I get to my parking/camping spot, I'll have to mark a new waypoint and convert that and mark it on the map in order to get a compass bearing and distance (that, or triangulate). Each of these is accurate to about 100 meters. Then I'd have to follow my compass bearing (and adjust for magnetic north) and estimate distance by pacing...whoo, boy--I can see being off by a lot. Thoughts, tips, tricks, links?

Edited by ByronForestPreserve

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Sounds like orienteering to me.... Isn't there already a badge for that?

 

Using true topo maps, compass and triangulation one can put themselves to within 2-3 meters, even better depending on the map scale used.

 

Standard methods prior to the implementation of GPS.

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No need for UTM.

 

Many cachers find caches all the time with nothing more than a good topo map and compass. Some have found thousands of caches that way.

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No need for UTM.

 

Many cachers find caches all the time with nothing more than a good topo map and compass. Some have found thousands of caches that way.

 

Unfortunately the badge specifically requires learning about and using UTM though the process does, as Gitchee-Gummee says, seem like it belongs more in an Orienteering badge than a Geocaching one.

 

How else could one mark a cache location on a topo map without getting its UTM coords?

 

I guess it just seems odd that they're asking to learn how to find a cache without a GPSr, when geocaching was started because of the availability of satellite data and GPS units in the first place.

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Sounds like orienteering to me.... Isn't there already a badge for that?

 

Using true topo maps, compass and triangulation one can put themselves to within 2-3 meters, even better depending on the map scale used.

 

Standard methods prior to the implementation of GPS.

 

I agree...I think maybe they're trying to sneak in an extra orienteering lesson.

 

What I don't get, though, is that the grid overlays are for the 1:24,000 topo maps; each line on the overlay tool is spaced at 100 meters. Seems to me that I'm estimating anything beyond that, both on the cache location and my starting point. Add needing to estimate the distance based on the map scale and pace it while walking...I don't think I'd ever get to within 2-3 meters! :)

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No need for UTM.

 

Many cachers find caches all the time with nothing more than a good topo map and compass. Some have found thousands of caches that way.

 

Unfortunately the badge specifically requires learning about and using UTM though the process does, as Gitchee-Gummee says, seem like it belongs more in an Orienteering badge than a Geocaching one.

 

How else could one mark a cache location on a topo map without getting its UTM coords?

 

I guess it just seems odd that they're asking to learn how to find a cache without a GPSr, when geocaching was started because of the availability of satellite data and GPS units in the first place.

 

Coordinates are coordinates, UTM, GMRS (?) OS, or just latitude and longitude in many forms... Just make sure that they clearly understand the need to be using the correct settings, and how to change between them.

 

Also VERY important is the need to make sure that when referencing a map and GPS that there are sometimes differences in the DATUM settings. Geocaching with GPS uses WGS84 datum and many topo maps can use different datum references when they were drawn up.

Common around North America you find newer maps in NAD 83 (very close if not the same as WGS84) and also NAD 27. In our area the difference can be over 200 metres for the same coordinates. Just make sure you use the correct ones when using GC (WGS84) then looking it up on a topo map... if both are the same fine, but if you get coordinates from GC and plot them on an NAD27 map you will be marking a point that isn't where you want to go... even though the coordinates are the same.

 

I'll think about it some more today... oh make sure they understand setting the compass for the local variants of North, that can be confusing to some. True North, Magnetic North and GRID North and their relationships can be very important in some areas. Many of the online declination calculators give Magnetic Declination results... between True North and Magnetic, Grid North is usually a bit different and has to be factored in for serious work.. depends on where you are but it can be plus or minus a few degrees on top of the declination. For many people it won't matter much since they can't follow a bearing worth a darn anyway... but Scouts should at least understand that part.

 

Back later.

 

Doug 7rxc

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What I don't get, though, is that the grid overlays are for the 1:24,000 topo maps; each line on the overlay tool is spaced at 100 meters. Seems to me that I'm estimating anything beyond that, both on the cache location and my starting point. Add needing to estimate the distance based on the map scale and pace it while walking...I don't think I'd ever get to within 2-3 meters! :)

 

To get within 2-3 meters (6-12 feet), you have to use either a precision distaince measuring system or sightings with a precision compass on two known objects (i.e. compass readings on two radio towers where the location is very accurately known).

 

Austin

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What I don't get, though, is that the grid overlays are for the 1:24,000 topo maps; each line on the overlay tool is spaced at 100 meters. Seems to me that I'm estimating anything beyond that, both on the cache location and my starting point. Add needing to estimate the distance based on the map scale and pace it while walking...I don't think I'd ever get to within 2-3 meters! :)

 

To get within 2-3 meters (6-12 feet), you have to use either a precision distaince measuring system or sightings with a precision compass on two known objects (i.e. compass readings on two radio towers where the location is very accurately known).

 

Austin

 

Geocaching.com's youtube channel has a video about geocaching without GPSr's. The gentleman has a good system of using topo and satellite maps to identifty local vegetation (think coniferious vs decidious tress, clearings, etc) to help him giure his way as close as possible before having to count off distance.

 

"I see it's 60meters from this point on the lake at a heading of 345degrees, so I only need to get to that point of the lake before I start counting paces and using a compass for heading"

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The only scouting requirement I founhd for UTM are:

 

c. Explain the UTM (Universal Transverse Mercator) system and how

it differs from the latitude/longitude system used for public

geocaches.

d. Show how to plot a UTM waypoint on a map. Compare the

accuracy to that found with a GPS unit.

 

Doesn't sound like you really need to actually go out in the field and find a cache using only UTM and a compass.

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What I don't get, though, is that the grid overlays are for the 1:24,000 topo maps; each line on the overlay tool is spaced at 100 meters. Seems to me that I'm estimating anything beyond that, both on the cache location and my starting point. Add needing to estimate the distance based on the map scale and pace it while walking...I don't think I'd ever get to within 2-3 meters! :)

 

To get within 2-3 meters (6-12 feet), you have to use either a precision distaince measuring system or sightings with a precision compass on two known objects (i.e. compass readings on two radio towers where the location is very accurately known).

 

Austin

 

Geocaching.com's youtube channel has a video about geocaching without GPSr's. The gentleman has a good system of using topo and satellite maps to identifty local vegetation (think coniferious vs decidious tress, clearings, etc) to help him giure his way as close as possible before having to count off distance.

 

"I see it's 60meters from this point on the lake at a heading of 345degrees, so I only need to get to that point of the lake before I start counting paces and using a compass for heading"

 

That only works if the location of the sat maps is correct. I have seen them be off by 200 feet (60 meters). It is a rare situation where the sat maps are closer than 2-3 meters.

 

Austin

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Sounds like orienteering to me.... Isn't there already a badge for that?

 

Using true topo maps, compass and triangulation one can put themselves to within 2-3 meters, even better depending on the map scale used.

 

Standard methods prior to the implementation of GPS.

 

I agree...I think maybe they're trying to sneak in an extra orienteering lesson.

 

What I don't get, though, is that the grid overlays are for the 1:24,000 topo maps; each line on the overlay tool is spaced at 100 meters. Seems to me that I'm estimating anything beyond that, both on the cache location and my starting point. Add needing to estimate the distance based on the map scale and pace it while walking...I don't think I'd ever get to within 2-3 meters! :)

You are correct, but you can get closer.

 

The process is referred to as 'interpolation'. Use of a fine-line metric ruler and a very sharp hard-lead pencil can put you as close or closer to pin-point accuracy as most consumer-grade GPSr units.

By use of a fine-line metric ruler, you have already cut that 100 meter distance down to 10 meters. Being careful with that very sharp pencil, should very well put you within a distance of less than 10 meters. Triangulation with that very-sharp pencil should easily place you within 2-3 meters. At that, you certainly would be within an acceptable 'perimeter' of GZ.

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The only scouting requirement I founhd for UTM are:

 

c. Explain the UTM (Universal Transverse Mercator) system and how

it differs from the latitude/longitude system used for public

geocaches.

d. Show how to plot a UTM waypoint on a map. Compare the

accuracy to that found with a GPS unit.

 

Doesn't sound like you really need to actually go out in the field and find a cache using only UTM and a compass.

 

The badge book goes into more detail. It says to locate "something" on the map and mark it (it suggests doing this with a landmark, though in that case I really don't know why it's in the Geocaching Badge book), then follow the GPS receiver to the same spot using its UTM coords and seeing how close we get to the projected coords we marked on the map. So though we're following the GPSr, we need to know how to plot the coords at the very least, and at that point discuss continuing from there as if we didn't have the GPSr.

 

I mean, it seems silly to do lessons on how to use UTM coords, and then pack it all away and tell them to ignore everything they just learned and just turn on their GPSr. Even though it seems like the entire subject is a little off-topic. Might as well follow through.

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The only scouting requirement I founhd for UTM are:

 

c. Explain the UTM (Universal Transverse Mercator) system and how

it differs from the latitude/longitude system used for public

geocaches.

d. Show how to plot a UTM waypoint on a map. Compare the

accuracy to that found with a GPS unit.

 

Doesn't sound like you really need to actually go out in the field and find a cache using only UTM and a compass.

 

The badge book goes into more detail. It says to locate "something" on the map and mark it (it suggests doing this with a landmark, though in that case I really don't know why it's in the Geocaching Badge book), then follow the GPS receiver to the same spot using its UTM coords and seeing how close we get to the projected coords we marked on the map. So though we're following the GPSr, we need to know how to plot the coords at the very least, and at that point discuss continuing from there as if we didn't have the GPSr.

 

I mean, it seems silly to do lessons on how to use UTM coords, and then pack it all away and tell them to ignore everything they just learned and just turn on their GPSr. Even though it seems like the entire subject is a little off-topic. Might as well follow through.

 

Busy week for me! Aside from the Scouts learning about the existence of other coordinate systems and that maps have the datum to figure in as well as things like 3 Norths and declination types, it sounds like they would do well to learn about how the UTM system is configured in use. I often teach map & compass, both to kids and adults. Things I like to make sure they are clear on include:

Be sure of the system in use and its components, they must match to work, also watch the dates on maps;

Regardless of the system and devices in use, make sure you actually read them correctly. I have no end of people that don't realize that the little marks in DMS have real significance. Degree, minute and second (if used) are distinct items... many look at the first number and assume it is degrees followed by minutes, where it might be minutes followed by seconds.;

Another thing specific to UTM grids... is that the location can be ANY location in the square formed up and to the right (NH) of the specified coordinates. How big that square is depends on the number of digits in the UTM coordinate set given. A ten metre square estimated from measured 100 metre grid is about the same as most GPS will give on a blah day. My first GPS was limited to a bit worse until SA was turned off / down about 15 metres. One should be easily able to that close at least, providing you got the datum part right.

 

I've got to run to dinner, but will keep watching. You can PM me if you like rather than discuss it too much here.

 

Doug 7rxc

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Busy week for me! Aside from the Scouts learning about the existence of other coordinate systems and that maps have the datum to figure in as well as things like 3 Norths and declination types, it sounds like they would do well to learn about how the UTM system is configured in use. I often teach map & compass, both to kids and adults. Things I like to make sure they are clear on include:

Be sure of the system in use and its components, they must match to work, also watch the dates on maps;

Regardless of the system and devices in use, make sure you actually read them correctly. I have no end of people that don't realize that the little marks in DMS have real significance. Degree, minute and second (if used) are distinct items... many look at the first number and assume it is degrees followed by minutes, where it might be minutes followed by seconds.;

Another thing specific to UTM grids... is that the location can be ANY location in the square formed up and to the right (NH) of the specified coordinates. How big that square is depends on the number of digits in the UTM coordinate set given. A ten metre square estimated from measured 100 metre grid is about the same as most GPS will give on a blah day. My first GPS was limited to a bit worse until SA was turned off / down about 15 metres. One should be easily able to that close at least, providing you got the datum part right.

 

I've got to run to dinner, but will keep watching. You can PM me if you like rather than discuss it too much here.

 

Doug 7rxc

 

Thanks! I'm glad everyone assures me that with a good estimate on the grid we should get almost as close as a GPSr often does. That was really my main concern, because I know they have orienteering badges, too (and is such a traditional Scout thing), and I didn't want to either dismiss map and compass use as less reliable nor get too complicated with this one aspect of the requirements. I think it would take more than a day just to really learn how to properly use UTM, add extra grid lines, triangulate, adjust for magnetic north, etc. without even touching on geocaching. All the things to look out for have been very helpful (and I'm learning a ton).

 

I think we'll go over how it works, mark a neaby cache on a topo map using UTM, but then find it with the GPSr and compare waypoints. That will fulfill the requirement and bag us a find.

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