Destroyed Referance Marks

[+slippeddisk]

Went looking for JW1441 yesterday. Did not find the station, but found RM#2 and the drill hole for RM#1. Both of which do not have an NGS data sheet. Is there any reason to report to the NGS that RM1 is missing?

Edited November 19, 2006 by slippeddisk

[Bill93]

If you did a thorough search for the main mark, that in itself is worth reporting.

Along with that, which RMs were found and not found can be included as useful information.

 

Tell briefly how hard you searched and what has happened to the area. For example "Mark not found. Area indicated by measurement from RM8 has been regraded for landscaping." or when you don't find anything to measure from "Not Found. None of objects in to-reach were positively identified and brief search with probe and metal detector at most likely location found no evidence of the mark" Since this one has ADJUSTED coordinates, if you didn't have RMs to measure from it would be worth mentioning that you searched 10 yards around coordinates as found by handheld GPS, but in this case measurements from the RMs would be more accurate so no need to mention GPS.

 

Think about what you would want to read in that report if you were assigned to look for the mark with no prior knowledge, and say it concisely.

[mloser]

Slippeddisk,

 

Did you measure from both RMs to the location of the disk and/or use a metal detector or probe. Since you located both reference marks you have a fairly easy method of finding the disk location by using the information on the datasheet to carefully measure the angles and distances from both reference marks to the station location. The point where the two measurements cross is the most likely location for the station, which is probably covered with dirt and leaves after not being found for years.

[+Holtie22]

Slippeddisk,

 

Sounds like you are closing in on this one! As mloser says, the next step is to measure from the RMs. Those measurements can be found on the NGS datasheet: RM1 - 16.357 METERS, Az. 081 degrees 19 minutes; RM2 - 13.313 METERS, Az. 138 degrees 33 minutes. (Note: the direction from the RM to the station will be 180 degrees from those published) Any sign of the Azimuth Mark?

 

This station includes a subsurface mark consisting of a bronze disk in a concrete block 3 feet below what used to be ground level. So even if the buried boulder is missing, (it was last seen in 1964), the subsurface mark may still be intact. Measure first, then dig!

 

Apparently, in 1957, an NGS party determined that the surface mark did not coincide with the subsurface mark, (did they move the boulder to look under it??), and they reset the surface mark accordingly.

 

With all this historical info to work from, I get the feeling that this mark can be found.

 

Holtie22

[Gnikhog]

slippeddisk,

One of the techniques I would use in a case like this is to measure from the found RM 2 disk to the drill hole that I believe to be RM 1. (From the JW1441 datasheet I calculate the distance and bearing from RM 2 to RM 1 to be approximately 47.4 ft at 30.5 dgr, true). Once I confirm the direction, distance, and that the drill hole is indeed where I expected the missing RM disk to be, I measure and mark from each reference mark back to where the station should be located - as noted by Holtie22. Using 2 (or more) RMs will generally improve search efficiency especially if you must dig beyond your probe or metal detector's detection depth. My theory is to dig smarter, not harder!

 

By the way, I always try to report the condition of RMs in my NGS and GC reports because I think it provides value to others who will attempt to recover and/or use a mark in the future.

 

Good luck!

[+slippeddisk]

Thanks to all of you for your input and words of encouragement. I think this one can be found. I was back today but had no equipment with me. Just looking around and getting the lay of the land. It's a hard area to work in alone. The banks of the old fort are about 8 to 10 feet high with trees growing out of them. The station should be at the top of the south breastworks, the RMs are in the ditch around the works. It will be hard to get steel tape up the slope and through the trees. I will enlist the help of family or friends when I return. It is a very neat old star shaped fort. You can still walk the top of the breastworks all the way around the star. But if you are not aware of what it is it just looks like a bunch of hills in the woods. I think I have found the area the Azimuth Mark is in, as I said I will be back with help and hope to find both the station and the Azimuth Mark. Once again thank for you help and encouragememt. I'll keep you posted.

 

Slippeddisk

[Bill93]

If you have to tape up a severe slope, be sure to bring some sort of plumb bob (improvised is fine) so that you can measure the horizontal distance and not the slope distance. Do it in as many short stretches as you need, with a stick or heel mark for the intermediate points.

[2oldfarts (the rockhounders)]

It's a hard area to work in alone. The banks of the old fort are about 8 to 10 feet high with trees growing out of them. The station should be at the top of the south breastworks, the RMs are in the ditch around the works. It will be hard to get steel tape up the slope and through the trees.

Slippeddisk

 

Why use a metal tape when you will be carrying the finest electronic tape available.

 

Yes, your GPSr will measure the distance to the nearest foot! The trick is to set a goto when you get to RM2. You need to set the goto to take advantage of the available satellite configuration at that time. The error of precision becomes moot since you just set the goto and will be using it at that time.

 

With the goto set for RM2, you move in the direction of the station disk until your GPSr tells you you are at the correct distance & bearing from RM2. Put a stake in the ground. Now repeat the process for RM1. You should now have 2 stake next to each other. Guess where the station's benchmark should be?

 

Your GPSr measures distance horizontally level (as the crow flies, so to speak.).

 

It works, we've done it on a number of difficult tri-stations.

This one was a tough one (no metal detecting allowed!), but the described system worked flawlessly.

 

John

[Bill93]

Using the GPS to measure distance may get you pretty close if you are out in the open with unobstructed view of satellites, a good constellation, a well-settled starting point, and not much time elapses before you get the second position found.

 

If you are under trees, I doubt the reading will be stable enough for that. Usually when I'm under trees the reading wanders 10 or 10's of feet while I stand there looking at it. Averaging a waypoint to see where you are can help. But under those circumstances it might be faster and more accurate to tape.

[2oldfarts (the rockhounders)]

When using the GPSr to measure distance you are dealing with the same satellite constellation from start to finish. Considering that you are only moving (on average) 100 - 150 feet tops for most RMs, the time factor is minimal. Unless it is extremely heavy tree cover (not likely this time of year) you should get adequate readings to get you to the correct position. It has worked on the Kaibab Nat'l Forest for us with no problems. We found a triangle blaze on a tree that was an RM, using this technique under the forest canopy!

 

The expected position error will be the same start to finish for each RM. You are only using the GPSr to measure the distance from the RM (waypoint you just set) to your current position. Your GPSr will give you the bearing to the RM from your current position, when it reads the same as on the datasheet, you will be on line and only need to move to the correct distance given on the datasheet. At that point you set a mark and then proceed to do the same thing for the other RM.

 

For this exercise you are NOT locating a precise point on the ground, but you are measuring the distance from a given waypoint that has just been defined. By measuring the distance from the RMs (waypoints just set) is how you will finally locate the precise point you are looking for.

 

The advantage is you just climb the hill to where the benchmark is located and avoid all the obstacles getting up the hill.

 

Put a tape measure in your pocket and if the canopy blocks the signal, then use it, but it will work using the GPSr as described. The idea is to find the station disk with the minimum effort as possible. Why fight the undergrowth if you don't need to?

 

John

[+Black Dog Trackers]

The precision of our GPS units:

 

A change in the last position of DDD.DDDDD is about 4 feet.

A change in the last position of DDD MM.MMM format is about 6 feet

A change in the last position of DDD MM SS.S format is about 10 feet.

 

For example,

40 01 50.1

076 30 12.8

is about 11 feet from

40 01 50.2

076 30 12.8

 

====================

 

The accuracy of our GPS units:

 

About +/- 12 feet or something like that; not too different from the precision.

(I don't remember the various specifications of WAAS and non-WAAS.)

[2oldfarts (the rockhounders)]

We use a Magellan Meridian GPSr. When we set a waypoint and do a "go to" for that waypoint the unit reads in hundredths of a mile until we get within 1/10 of a mile then it changes to feet.

 

If the datasheet says the benchmark is 150 from the centerline of the old highway, you walk to the centerline and set a waypoint. Head in the direction of the benchmark and do a go to, to the waypoint that was just set. The unit will read the number of feet from that waypoint. If you walk in a straight line perpendicular to the centerline, you will see when you are 150 away from it.

 

The precision of the unit in determining DD.DDDDD is secondary to the measurement of the distance you just moved from the set waypoint, for this application. The unit will give you reliable distance and bearing reading to the waypoint. Our unit is set to DD MM.mmm which is approximately 6 feet per .001 minute, yet when you read the distance to the waypoint it will show less than 6 feet to go. Does that mean the precision of the unit is flawed? No, it is just a different calculation that the GPSr does with the signal it receives.

 

The key factor for this to work is to set the waypoint under the same conditions as when they will be used. You Can Not set the waypoint today and do the measurement tomorrow because the satellite configuration & conditions will have changed.

 

John

 

edited for clarity.

Edited November 21, 2006 by 2oldfarts (the rockhounders)

[Bill93]

The test of how well John's technique will work is to set a waypoint under the conditions where you will be working, GOTO that same waypoint, and then just stand there for the time it would have taken you to get to the other position of interest. See how much the distance varies from zero in that time and know that the accuracy of your distance measurement won't be any better than the wandering you see in the display.

 

Since most units give distance to much finer resolution,, the 4, 6, 10 ft numbers for lat-lon display are irrelevant here.

[2oldfarts (the rockhounders)]

The test of how well John's technique will work is to set a waypoint under the conditions where you will be working, GOTO that same waypoint, and then just stand there for the time it would have taken you to get to the other position of interest. See how much the distance varies from zero in that time and know that the accuracy of your distance measurement won't be any better than the wandering you see in the display.

 

Since most units give distance to much finer resolution,, the 4, 6, 10 ft numbers for lat-lon display are irrelevant here.

 

The test for this technique is to try it on a known triangulation station. Measure from each of the RMs and see how close you get to the station disk.

 

John

[+Black Dog Trackers]

I plan to do the test with a tape measure; 100 feet.

However, I do agree with Bill93 that actually no distance is required for the test.

Edited November 21, 2006 by Black Dog Trackers

[+slippeddisk]

JW1441''RECOVERY NOTE BY COAST AND GEODETIC SURVEY 1957 (JCC)

JW1441''THE AZIMUTH MARK AND TWO REFERENCE MARKS WERE RECOVERED

JW1441''IN GOOD CONDITION. THE DISTANCE AND DIRECTIONS TO REFERENCE

JW1441''MARKS AND AZIMUTH MARK FAILED TO CHECK AFTER REPLACING COPPER

JW1441''WASHER SET BY A LOCAL ENGINEER IN THE DRILL HOLE OF THE

JW1441''ORIGINAL MARK. A CHECK WAS MADE WITH THE SUBSURFACE MARK

JW1441''AND THE MARK SET BY A LOCAL ENGINEER WAS FOUND TO BE OUT

JW1441''OF POSITION. A NEW MARK WAS SET HOLDING THE SUBSURFACE

JW1441''MARK AS TRUE POSITION.

JW1441''THE STATION MARK, STAMPED WINCHESTER 1933 1957 AND SET IN

JW1441''A DRILL HOLE IN A BURIED BOULDER THAT PROJECTS 4 IN., IS

JW1441''ON THE S SIDE AND THE HIGHEST POINT OF THE HILL

 

Help me out here please. Is this saying the the new mark is not in the same place as the old one? The local used the original drill hole but it was found to be out of position. Did they set a new disk in another boulder on the south side of the hill?

 

slippeddisk

[+Holtie22]

That's what I was wondering with my remark about looking under the boulder for the subsurface mark. Apparently, at some point the original disk went missing and was replaced by a copper washer. Subsequently, a measurement from the RMs revealed a discrepancy in the location of the washer, indicating that perhaps the boulder had moved? This was confirmed by "checking" the subsurface mark. Did they actually move the boulder - how else could they "check"? They then set a new disk coincident with the reference marks and subsurface mark in the boulder. That's a lot of boulder-moving!!! The position of the station has not changed, but the location of the boulder apparently has. Is the boulder gone completely?

[+slippeddisk]

That's what I was wondering with my remark about looking under the boulder for the subsurface mark. Apparently, at some point the original disk went missing and was replaced by a copper washer. Subsequently, a measurement from the RMs revealed a discrepancy in the location of the washer, indicating that perhaps the boulder had moved? This was confirmed by "checking" the subsurface mark. Did they actually move the boulder - how else could they "check"? They then set a new disk coincident with the reference marks and subsurface mark in the boulder. That's a lot of boulder-moving!!! The position of the station has not changed, but the location of the boulder apparently has. Is the boulder gone completely?

 

I see no boulder in the area in question. There are however two depressions in the ground that may have once contained the boulders. I can't be sure of that because the area has been hunted by relic hunters since the day the war ended. There are uncovered holes all over the place.

[2oldfarts (the rockhounders)]

I plan to do the test with a tape measure; 100 feet.

However, I do agree with Bill93 that actually no distance is required for the test.

 

If you try it with an actual Triangulation station you will be able to verify the ability to check the bearing to the RMs as well as the distances.

 

John

[+Holtie22]

When the mark was reset in the boulder, it projected just 4" out of the ground. No mention of the size of the boulder, but to me, the word means something larger than a rock that I can move by myself. Archimedes may have a different take on that, however...

 

The last sighting of the disk, in 1964, confirms that the boulder projects just 4". So we're back to the original advice - if the RMs seem to be in their original locations, (see Gnikhog's post for a way to check on that), then it is a simple matter, using whatever measuring method you prefer, (we're not talking large distances, here!), to establish the location of the station with a reasonably high degree of confidence. Then... you dig. The subsurface mark was down 3 feet when initially placed. Is there a depression at the location indicated by measurements from the RMs that could account for both the missing boulder and the concrete block of unspecified size that contained the subsurface mark? If so, then maybe this one really is gone.

[+Black Dog Trackers]

If I were faced with digging several inches, I'd be using a tape measure to find the location from the RMs.

[mloser]

I'll echo what BDT said. I would measure as carefully as possible (I know that shrubs and hills make it more difficult, but that is what we are often left to work with) and then use a metal detector if possible to help pinpoint the location. By using both reference mark locations it should be possible to get very close to the actual station location before digging. I wouldn't expect the boulder to protrude. If there is a hole at that location, then it is likely someone moved the boulder and you might check for the u nderground mark. I have yet to see one of those, despite spending some time digging for one where I found the monument for the station pushed over.

[2oldfarts (the rockhounders)]

Well, I went out to a "Known" Triangulation Station today to get some pictures with the GPSr to show how well it works for measuring distances.

 

Did I get a surprise or what?!!!

 

I went to this benchmark we had previously found and went to RM 2 got a waypoint and went over to the station disk. I put the GPSr on the disk and took the picture.

 

 

Then I went to RM 1 and set a new waypoint and went back to the station disk. Set the GPSr on it again and took the picture.

 

 

I went back to the truck and checked the pictures against the datasheet boxscore using GSAK.

 

GP0601| FALL RM 1 11.582 METERS 08535

GP0601| FALL RM 2 16.437 METERS 18516

 

If you compare the GPSr to RM 1, 11.5 meters is 34.5 feet, but the bearing is not 85°!

 

At this point I got out the handheld compass and verified the direction and bearing to RM 1.

 

and here

 

Looking at the compass you see the datasheet is wrong on the bearing to RM 1!

 

Now comes the really fun part of this little test. If you read the written description for RM 2 the distance is different there than in the boxscore!

 

GP0601''REFERENCE MARK 2 IS A STANDARD DISK, STAMPED FALL NO 2 1963,

GP0601''SET IN THE TOP OF A CONCRETE MONUMENT PROJECTING 5 INCHES.

GP0601''IT IS 59.3 FEET SOUTH OF THE WITNESS POST.

 

The GPSr matches the distance in the box score & not the written description.

 

I was getting a bit disconcerted over having chosen a lousy Tri-station to use, that I decided to go find a benchmark for real using this method!

 

The mark I chose is one that I couldn't find in the past because the mark was buried and the witness post was gone, the milage sign didn't match up, the windmill was gone, & there was no number on the utility poles nearby! A tough cookie to crack.

 

The log says it all, and the system proved itself again.

 

K 404 found log.

 

In the end, a Very Good day!

 

John

[+Colorado Cacher]

Amazing isn't it, I found one completely pulled out of the ground when I placed "Helen's bald Spot," I wonder who teh jerk was that did it.

[AZcachemeister]

When using the GPSr to measure distance you are dealing with the same satellite constellation from start to finish. Considering that you are only moving (on average) 100 - 150 feet tops for most RMs, the time factor is minimal. Unless it is extremely heavy tree cover (not likely this time of year) you should get adequate readings to get you to the correct position. It has worked on the Kaibab Nat'l Forest for us with no problems. We found a triangle blaze on a tree that was an RM, using this technique under the forest canopy!

 

The expected position error will be the same start to finish for each RM. You are only using the GPSr to measure the distance from the RM (waypoint you just set) to your current position. Your GPSr will give you the bearing to the RM from your current position, when it reads the same as on the datasheet, you will be on line and only need to move to the correct distance given on the datasheet. At that point you set a mark and then proceed to do the same thing for the other RM.

 

For this exercise you are NOT locating a precise point on the ground, but you are measuring the distance from a given waypoint that has just been defined. By measuring the distance from the RMs (waypoints just set) is how you will finally locate the precise point you are looking for.

 

The advantage is you just climb the hill to where the benchmark is located and avoid all the obstacles getting up the hill.

 

Put a tape measure in your pocket and if the canopy blocks the signal, then use it, but it will work using the GPSr as described. The idea is to find the station disk with the minimum effort as possible. Why fight the undergrowth if you don't need to?

 

John

 

I have done this, and it worked for me.

I have also tried it, and had to come back with a tape.

Depending on the terrain, you may have little option. It sounds as if you are dealing with the 'little option' type terrain. Letting the GPSr settle for an extended period may help if there is overhead vegetation, but obviously your precision will be diluted by the changing satellite positions if you wait too long.

[+Black Dog Trackers]

I tested this measuring method today. I posted the results over here.