Reference mark Arrows

September 28, 2008

I'm currently trying to recover a station but have only one reference mark located. I do have a clear view towards the station area but if there, it's buried fairly deep. When reference marks are set, are the arrows sighted visually towards the station or are they calculated using some other means? At 57 feet away, I thought a visual alignment using the arrow would prove closer than a compass alignment if the arrow can be trusted as accurate. The reference Mark disk is solidly set. Your thoughts?

1.2k · September 28, 2008

Excellent question. And like many other questions related to benchmarks, the answer is: "It depends." [Grin.]

The intention when setting a reference mark is for the arrow to point exactly toward the station. However, the database contains many reports advising that "the arrow on the reference mark disk points away from the station". While it is possible that the monumenting party made a mistake (probably accompanied by a burst of profanity when they realized their error), the most likely cause is that the mark has been disturbed.

EZ4734 COATS 1949 GEOCAC (PFF)
THE COORDINATES FOR THE STATION FALL UNDER PAVEMENT.

REFERENCE MARK NO.1 WAS RECOVERED IN THE FRONT YARD OF MR. J.E. PARRISH (PARCEL NR. 0690-74-9078.000). THE DISK IS RECESSED 4 CM AND THE ARROW POINTS AWAY FROM THE STATION. RM1 IS 5.2 FEET EAST OF A 20 INCH CEDAR AND 33 FEET EAST OF THE CENTER LINE OF N. RAILROAD STREET. THE COORDINATES (BY NGS FORWARD) ARE N35 24 33.74453 W078 40 16.37360. USE WITH CAUTION. POSSIBLY DISTURBED. (SEE 1972 RECOVERY NOTES.)

REFERENCE MARK NO.2 WAS RECOVERED ON PARCEL NR. 0690-74-8062.000. THE TOP OF THE MONUMENT IS BROKEN OFF AND THE DISK AND SHANK ARE MISSING. RM2 IS 34 FEET NORTH OF THE NW CORNER OF A METAL FREIGHT BUILDING, AND 109 FEET WEST OF THE CENTERLINE OF N. RAILROAD STREET. THE COORDINATES (BY NGS FORWARD) ARE N35 24 33.15532 W078 40 17.85846.

1/1/1972 by NCGS (MARK NOT FOUND)RECOVERY NOTE BY NORTH CAROLINA GEODETIC SURVEY 1972 (JWC) COATS PROBABLY LOST, (SEE NOTE BELOW) 113 (NCGS) GOOD - SOME CONCRETE BROKEN RM 2 DISK GONE RM 1 ARROW POINTING IN OPPOSITE DIRECTION FROM STATION 113 (NCGS) AZ. MARK UNABLE TO LOCATE REFERENCES PLACE STATION UNDER PAVED STREET.

1/1/1972 by USGS (MARK NOT FOUND)RECOVERY NOTE BY US GEOLOGICAL SURVEY 1972 (MKW) STA. MARK BELIEVED DESTROYED. STREET HAS BEEN RELOCATED AND TAPED DISTANCES NOW MEASURE TO A POINT ON PAVED STREET. RM 1 LOCATED, BUT IT IS LEANING AND EVIDENTLY WAS KNOCKED OUT OF GRD. AND REPLACED BECAUSE ARROW ON TABLET POINTS ABOUT 180 DEG IN ERROR. RM2 NOT FOUND AND BELIEVED DESTROYED. 113(NCGS) LOCATED AND REPORTED ON SEPARATE FORM. 113(NCGS) AZ.MK. NOT SEARCHED FOR.

A couple of notes about my report. This text was copied from the GEOCACHING.COM website. The reported coordinates were in DDMMSS format in the report sent to NGS. Second, I referenced the 1972 reports because there are a lot of recovery reports for this station and the RM1 arrow problem got superseeded by subsequent reports which do not mention the reference marks. And, of course, I added the red highlighting for this post. Don't we wish that was a data sheet feature!

In addition to the arrow being mis-oriented, the distance to the station sometimes does not "check" against the original notes. Again, this is a clue that the reference mark may have been reset by a non-professional.

So, back to the station you are trying to recover. Certainly, you will want to check the arrow with your compass. While you will not be able to detect minor errors, you might find that the arrow is 180 degrees off, in which case you should walk in the direction indicated by your compass.

If your GPS device has a "project a waypoint" feature, you can stand on the mark and let the unit predict where the main station should be. Another techique is to stand on the reference mark and let the GPS receiver stabilize for a minute. Then set a waypoint. (Use the "averaging" function, if your unit has it.) Then walk away from the reference mark and find a point where the distance and bearing to the reference mark are the same as the distance and bearing given in the "box score" of the data sheet. At that point, you should be very, very close to the station. Why? Because when you set a waypoint at the reference mark, you offset any errors in position readings being caused by external factors.

Of course, the most accurate method is ground measurement with a 100-foot tape. Measure from every reference point you can find, and mark each distance and general bearing in an arc as you "swing" from the reference point. Where the arcs intersect is the point to begin probing/digging.

-Paul-

September 28, 2008

Hi Chiknlips45--

I guess I would have to say that a goodly percentage (20%?) of the marks I recover are not oriented precisely to the station to which they refer, varying from a few degrees to big errors (30d or more). [And this seems to be due to mis-setting by the installers, not later damage or abuse by others.]

The Other Paul speaks the truth. :rolleyes: If I'm trying to find the station, I almost always tape from the RM, using the back bearing of the azimuth to that mark which is given in the box score (which is supposed to be the bearing from the station to the RM). I lay the tape out on the ground for 25 ft. or so and then measure the bearing of the tape. My compass will sight along it through an extended "peephole" while enabling me to see the tape through a "window" in the base of the compass, and this seems to be accurate to within 1d or so. You can also lay a baseplate-type compass down beside your tape and orient it carefully to the tape to check the bearing. Here's an example.

But as Paul said, beware the back bearing (180d off the actual direction). I find quite a few sites described in the 1930s in which the bearings reported in the text (and sometimes in the box score) are not direct bearings but back bearings. The site I mentioned above is a recent example of this, in which two of the box score bearings to RMs are back bearings and the third one is direct. [At this site, however, the orienting arrows on the RMs are fairly accurate. Go figure!]

Here is another example of trying to find a station in the absence of any usable tie-ins in the old Description (due to changes over time), just by taping from a GPSr-provided estimate of the station's location (or from a single RM).

Good luck!

-Paul

Edited September 28, 2008 by pgrig

September 28, 2008

Paul and Paul, thanks for the advice and recommendations. I'm sure the bearing is not reversed since the station is adjusted and my GPS zeros out in the correct direction. There's also some small stakes in the area of the main station that ensure I'm on the right track. I 'll put less emphasis on following the arrow of the reference marks and pay more attention to my compass and tape. For some reason, when on site, the excitement and thrill of the hunt tend to cloud my mind from common sense approaches to finding the station. Thanks again for the sound advice.

Mike

September 29, 2008

Howdy! Which station are you searching out? Want some help with a long tape & short shovel on site? I might be able to break away one evening later this week to lend a hand...

September 30, 2008

Howdy! Which station are you searching out? Want some help with a long tape & short shovel on site? I might be able to break away one evening later this week to lend a hand...

NorthWes, I'd really enjoy the help. Later on in the week may work for me but I'm not sure yet . The station is UV4396. RM3 is the only mark recovered. It was an obvious find. I had to obtain a permit from Eklutna Inc in Eagle River to tresspass on their property. I'll shoot you an E-mail with more specifics and contact information if that's OK with you?

1.2k · September 30, 2008

After reading the description for UV4396, I have lots of admiration for those of you who are willing to take on the search for a mark where professionals came in by helicopter!

Here are the coordinates for the other two reference marks, in case you don't have them.

-Paul-

REFERENCE MARK NO. 1: N61 28 07.17820, W149 22 37.12829

REFERENCE MARK NO. 2: N61 28 06.76667, W149 22 39.43375

Edited September 30, 2008 by PFF

7.9k · September 30, 2008

In my experience, the RM arrow always points in the general direction of the station...but not always precisely so. That's why they publish the bearing angle.

Really, though, how hard can it be to locate a seven foot orange pole? :laughing:

September 30, 2008

Howdy! Which station are you searching out? Want some help with a long tape & short shovel on site? I might be able to break away one evening later this week to lend a hand...

NorthWes, I'd really enjoy the help. Later on in the week may work for me but I'm not sure yet . The station is UV4396. RM3 is the only mark recovered. It was an obvious find. I had to obtain a permit from Eklutna Inc in Eagle River to tresspass on their property. I'll shoot you an E-mail with more specifics and contact information if that's OK with you?

I'll watch for the email!

September 30, 2008

The arrows on Reference Marks were oriented by visually sighting on the triangulation station. They might not be perfect but should be close. Angles were turned from the triangulation station to the reference marks (at least 6 readings on each RM were taken and then averaged). The distances were measured to each RM in both feet and meters and then checked.

GeorgeL

NGS

October 1, 2008

The distances were measured to each RM in both feet and meters and then checked.

GeorgeL

NGS

George,

I always really appreciate seeing your professional feedback.

Did they actually measure in both feet and meters or did they just measure in one format and then convert to the other?

Thanks,

October 1, 2008

TillaMurphs, Here is a quote from USC&GS Special Pub #247, page 98:

"Measurements to reference marks.-Measurements from the station mark to each

reference mark should be carefully made independently in feet to hundredths and in

meters to thousandths. A 30-meter (100-foot) steel tape marked in meters on one side

and in feet on the other side is usually used. Measurements should be made horizontally

if possible, using a plumb line or plumb benches if necessary (see fig. 54). When each

measurement is made, it should be recorded directly into the record book. Also the

check conversion computation of feet to meters should be shown. Measurements in feet

and meters should be repeated until a check is obtained to 0.003 meter. A good method

for obtaining completely independent measurements in feet and meters, is to hold the

zero foot mark of the tape on the station mark, and read the feet, tent>hs,a nd hundredths

at the reference mark. Then using the other side of the tape, hold the nearest greater

decimeter mark on the reference mark, and read the set-back in centimeters and millimeters

at the station mark. All original tape readings, including the set-back reading,

and arithmetic computation of the final distance should be shown in the record book.

Additional measurements directly between reference marks should also be made as a

check , when practicable."

The short answer is, yes, two independent measurements were made.

GeorgeL

NGS

October 3, 2008

TillaMurphs, Here is a quote from USC&GS Special Pub #247, page 98:...

"A good method for obtaining completely independent measurements in feet and meters, is to hold the

zero foot mark of the tape on the station mark, and read the feet, tent>hs,a nd hundredths

at the reference mark. Then using the other side of the tape, hold the nearest greater

decimeter mark on the reference mark, and read the set-back in centimeters and millimeters

at the station mark."

The short answer is, yes, two independent measurements were made.

GeorgeL

George,

Thank you for your valuable information.

Actually, using a double-sided tape and then recording both sides is not a bad idea. That way, when we get back home we can convert and make sure both measurements agree – a good double-check that we did not make any mistakes when reading or recording the measurements.

October 3, 2008

I would recommend checking in the field with a pocket calculator. If you wait until you get home and they disagree, you won't know which is correct, if either.

GeorgeL

NGS

October 4, 2008

Maybe some did not notice the other check. I’m referring to the way the measurements are taken. The first measurement is pretty straight forward with the end of the tape over the station and the person at the reference mark reading the tape. The second measurement is made with the person at the reference mark aligning an even meter/foot mark and the person at the station taking the reading. This way they swap the “smart” end of the tape.

Two different types of measurements by two different people reduces the possibilities of errors. Great idea.

1.2k · October 4, 2008

Forget the arrow direction, for a moment. Consider times when the written directions are backward. [Grin.]

A DIFFERENCE WAS FOUND IN THE DISTANCE TO THE MARKS AND A SMALL DIFFERENCE WAS FOUND IN THE DIRECTION TO REFERENCE MARK NO. 1. THE BEARING AND DIRECTION TO REFERENCE MARK NO. 2 WERE LISTED IN ERROR OF 180 DEGREES AND OTHERWISE THE DIRECTION WAS CHECKED. AIRLINE DISTANCE AND DIRECTION FROM NEAREST TOWN 1 MILE SOUTH OF CUMNOCK.

That's from the text of the main station (EZ1301). The reverse-direction alert never made it into the description of the reference mark's PID (EZ1300). It's a mute point, since the station and its two reference marks were destroyed intentionally because they were in the path of a new 4-lane highway.

A new triangulation station (EZ1302) with reference marks 3 and 4, was established on the right-of-way of the new highway. The original azimuth mark still remains, about a half-mile away. How about the arrow on that disk? Well, either by luck or design, the bearing is less than one degree different. (The box score shows 175.4 degrees to the old station and 176.2 to the new station.)

Back to the original answer to the arrow accuracy question. It's still, "It depends." However, a lot of excellent insight has been presented in subsequent posts. Thanks, everyone!!

-Paul-

1.2k · October 4, 2008

Forget the arrow direction, for a moment. Consider times when the written directions are backward. [Grin.]

.. And, sometimes it's not even degrees, but just simple N/S directions:

EE0050'OF THE MAIN STREETS OF THE TWO TOWNS, ABOUT 325 FEET W OF W END OF
EE0050'NO. 76 RAILROAD 85-FOOT TIMBER TRESTLE, AN ESTIMATED 30 YARDS N

EE0050'OF THE TOP OF N BANK OF TOCCOA RIVER, 80 FEET W OF A TELEPHONE

EE0050'POLE, IN THE LINE OF THE POLES, 30.7 FEET S OF S RAIL, 2.3 FEET

EE0050'LOWER THAN TOP OF SAME, AND PROJECTING 0.3 FOOT.

.....

EE0050'SUBDIVISION. MARK IS 30.3FT NORTH OF NORTHERN RAIL, ON THE SE SIDE OF

EE0050'CLEARING FOR THE POWERLINES, AND ABOUT 50FT SE OF CENTER OF

EE0050'POWERLINES.

The team that monumented this mark got E/W directions proper, but they were turned backwards for N/S. Good thing for the railroad, 'cuz I don't think they knew they were supposed to be on the other side of the river.

It's funny that the arrows have come up now, after all these years. I recently found a mark that the one remaining RM disk was off by a noticeable amount. Not major but looking at it visually, you could see that it wasn't in line. That was when I realized that the arrows probably weren't set scientifically - just as best as the team could get it.

October 6, 2008

Well, I had the real pleasure of going afield with chiknlips45 to recover this mark on Oct 4 2008. Check out his recovery log to see how well-prepared he was for this find. We got into the location after a short 'pack' through frosted marshgrass and 'dug into' our work with gusto. The arrow on RM3 was within several degrees of satisfying our compasses of its accuracy, and (as our recovery logs show) with one RM in hand we were able to find all the reference marks and the main station (ok - the base of RM1 was all we found... but we considered that remarkable.) The location was stunning beautiful, and we were inspired to look for several more in the area (including one that raised my eyebrows and made me realize I may have logged 5 marks as destroyed when they may not be - but that's another thread...)

October 6, 2008

A beautiful recovery, with photography to match! Getting those "bottom of the hole" shots was excellent!

10k · October 10, 2008

Hmm... Don't know what to make of this! We're having a controversy about the highest point in Passaic County. Using the info from CountyHighPointers. So, being the evil dolphin I am, I set out a cache a few months back at Point 1. (Nasty bushwhack!) Today, I went back to finish the chore, with Points 2 & 3, near

LY2652. I found the station, but didn't look for the reference marks in 2004. I returned to find all but one referece mark last year. The mark I didn't find was an arrowhead. Okay. All is well. Looking for CountyHighPointers Point 3 today, I discovered that, at that location, is the stem of a disk! It's about 450 feet southeast of Bearfort Reset 1942. There is no disk listed for this location! This is the middle of nowhere! It took me two hours to hike to this location!

Thoughts?

October 15, 2008

Maybe you found the stem of a disk set by another agency, possibly the USGS. Many such marks are not in the geocaching database.

June 14, 2009

What happens if you have two RM's but neither one have any bearings with them. Like this station here cook

We found RM1 and the arrow on it but have no idea where the station is or how far it is in the direction of the arrow. We did head that direction but nothing was found.

The trees that are given at reference points are no longer there and other have grown up with lots of underbrush.

Any help would be greatly appreciated.

4.1k · June 14, 2009

What happens if you have two RM's but neither one have any bearings with them. Like this station here cook

We found RM1 and the arrow on it but have no idea where the station is or how far it is in the direction of the arrow. We did head that direction but nothing was found.

The trees that are given at reference points are no longer there and other have grown up with lots of underbrush.

Any help would be greatly appreciated.

The mark you are seeking has adjusted coordinates and your GPSr should take you to within 10-15 feet of the disk. Start at the reference mark and follow the arrow on it and when your GPSr says 0 feet to go you should be able to see where the mark is or was.

John

June 14, 2009

What happens if you have two RM's but neither one have any bearings with them. Like this station here cook

We found RM1 and the arrow on it but have no idea where the station is or how far it is in the direction of the arrow. We did head that direction but nothing was found.

The trees that are given at reference points are no longer there and other have grown up with lots of underbrush.

Any help would be greatly appreciated.

It sounds to me like they didn't measure from RM 1 to RM 2 to give a check on their measurements, but they did measure from the RMs to the station. The geocaching page doesn't include this information, but the datasheet does (from the geocaching page you can follow the link view the original datasheet) and find that the distance from the station to RM 1 is 22.036 meters at an azimuth of 006° 08'. Since you have found the reference mark, you'll want to reverse that azimuth to 186° 08' to go to the station.

June 14, 2009

Thanks guys. Your help has been great. We are pretty new to benchmarking but are finding it really cool for lack of a better word LOL.

We are thinking also that it might be easier find the marks in the winter when the plants are dormant and visibility might be better. All that green leafy foliage will be gone. It was by pure dang luck we found RM1.

June 15, 2009

What happens if you have two RM's but neither one have any bearings with them. Like this station here cook

We found RM1 and the arrow on it but have no idea where the station is or how far it is in the direction of the arrow. We did head that direction but nothing was found.

The trees that are given at reference points are no longer there and other have grown up with lots of underbrush.

Any help would be greatly appreciated.

A portion of the datasheet called the "boxscore" contains the info you want (distance and azimuth FROM the station):

BX2967|---------------------------------------------------------------------|
BX2967| PID	Reference Object					 Distance	  Geod. Az  |
BX2967|														   dddmmss.s |
BX2967|		COOK RM 1							22.036 METERS 00607	 |
BX2967|		COOK RM 2							20.989 METERS 21538	 |
BX2967| BX2989 MILAM SABINE R AUTH KHT 89		  APPROX.15.4 KM 2821327.8 |
BX2967| BX2990 CHAMBERS HILL LOT				   APPROX.16.0 KM 2834623.5 |
BX2967| BX2991 CHAMBERS							APPROX.16.0 KM 2834759.4 |
BX2967|---------------------------------------------------------------------|

June 19, 2009

That's awesome. Thanks for the great help. We're gonna give it another try this weekend. At least this time we'll be prepared for the stinging nettles. Man those hurt.

June 19, 2009

That's awesome. Thanks for the great help. We're gonna give it another try this weekend. At least this time we'll be prepared for the stinging nettles. Man those hurt.

2.7k · June 19, 2009

Team Gryarvold -

If the RMs prove difficult to find, it might help to remember that the box score azimuths are True North, not Magnetic North. At distances like 20 meters it will possibly make a difference.

1.5k · June 19, 2009

...........

Edited June 19, 2009 by Z15

Reference mark Arrows

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