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NGS Surveyor

Survey Mark Recovery Instructions

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I just completed a "cookbook" of instructions for recovering a survey mark for a work project. I consulted several sources, including the Geocaching "Frequently Asked Questions". See what you think.






A. DATASHEET - Obtain and study the mark’s datasheet (description), including all recovery notes, and highlight key points (such as: the number of reference marks, the distance from the edge of a road, etc.) and any flag any discrepancies found. U.S. Coast & Geodetic Survey and National Geodetic Survey (NGS) marks and some others are in the NGS database at: http://www.ngs.noaa.gov/cgi-bin/datasheet.prl . For a sample NGS datasheet, with explanations, see: http://www.ngs.noaa.gov/cgi-bin/dsformat.prl . Recent recoveries and photos of many marks can be found on the Geocaching.com web site.


B. DATABASE SEARCH - Perform a NGS database search for other nearby survey marks (radial search at: http://www.ngs.noaa.gov/cgi-bin/ds_radius.prl . This information may be helpful in finding the intended mark and may help avoid confusion at the site.

C. MAPS - Obtain maps, aerial imagery and/or satellite imagery of the area (paper or digital).

D. COMPUTE POSITIONS - Recommend computing the positions of Reference Marks (RMs) and any other nearby marks, and consider computing the distances between RMs and any other marks. The “box score” on the datasheet lists the directions and distances to RMs and any other marks, and the “Forward” on-line software at: http://www.ngs.noaa.gov/TOOLS/Inv_Fwd/Inv_Fwd.html can be used to do the computation. Once “Forward” has been used to compute the positions, the “Inverse” software can be used to compute the distance between known points.

E. PLOT - Recommend plotting all marks on the map and/or imagery at a scale to show surrounding features. Check features in the imagery against the description (near a road, on a hill top, etc.), and then attempt to resolve any discrepancies and contradictions.

F. EQUIPMENT - Gather recovery equipment including: mark description, map, magnetic compass, 100 – 300 ft tape, shovel, long screwdriver (to hold one end of tape), whisk broom, camera, GPS receiver, scientific calculator, and, optionally, tile probe, metal detector. Also, a yellow crayon or white powder can improve the photos by highlighting the stampings.

G. TRAVEL - To travel to the mark the original and “hard-core” way, travel to the beginning of the description’s “To Reach” and follow the “To Reach” using the vehicle’s odometer, and left and right turns as listed in the description. Otherwise, enter the position into the GPS receiver (GPSr) and follow the GPSr’s directions (making sure to use the NAD 83 or WGS 84 datum).

H. PERMISSION - Request property owner permission as necessary.

I. COMPLETE TRAVEL - Continue travel to the immediate vicinity of the mark and do a visual search for:

1. Reference objects mentioned in the description (edge of roads, bridges, buildings, fence-lines, telephone poles, etc.),

2. Witness Posts

3. Remains from previous occupations (wood, wire, slight depression, etc.)

4. Survey marks

J. FIND - Use distances, angles, and other information from the description to narrow the search, (eg, the distance from a road or fence, witness post, reference mark, etc., the type of mark: concrete monument, disk in bedrock, etc.). If not found, review the datasheet for additional clues.

K. MEASURE - Once some of the objects and/or marks are found, use a magnetic compass to determine the approximate directions and measure the distances by pacing or taping from the witness post, reference marks, and other reference objects. Mark the arc of each distance and intersect the distance arcs, as required. Use any vertical information provided, such as distance above or below road or railroad track. When using a magnetic compass be sure to correct for the magnetic declination (difference between true north and magnetic north). The value can be obtained from: http://www.ngdc.noaa.gov/geomagmodels/Declination.jsp . If the main station is found first, use a compass and pacing or taping to locate the RMs. If an RM is found first, use the direction of the RM’s arrow and the distance stated on the Datasheet to help find the main station. Also, the “Back Azimuth” from the “Forward” computation for that RM will provide the azimuth from the RM back to the Triangulation Station.

L. GPS - Remember when searching using GPS that most vertical control points have only scaled positions with a 6 arc-second error tolerance (about 600 ft); the description may get you much closer to the mark than a GPSr with the scaled coordinates. Combine GPS results with other clues. Most horizontal control points have coordinates that are much better than a hand-held GPS receiver (GPSr). A hand-held GPSr may only be accurate to 6-8 meters, perhaps 1-2 meters if equipped with WAAS and if the WAAS signal is available. Thick trees are a definite challenge for a GPSr. (WAAS = Wide Area Augmentation System, operated by the FAA.)


M. CHECK DESCRIPTION - For all marks found, check the description elements such as: (1) the name of the agency cast into the disk or logo cap, (2) the type of disk (RM, Azimuth Mark, etc.) cast into the disk, (3) the exact name and date stamped, and (4) the type of setting (bedrock, concrete, etc.). Check all information on the survey disk against what is stated on the Datasheet. Avoid false recoveries. Also avoid false “destroyed” notices. Note, and ideally resolve, any discrepancies. In the Recovery Note, list significant changes and discrepancies.

N. GROUND CHECK - For all marks found, visually check them to see if they appear disturbed. Then check them by taping the distances between the marks and any other usable references, and compare them to published and computed values. Note the direction (to at least the nearest 45 degrees--NE, NW, etc.) from the main Triangulation Station to each RM. Note any significant differences from what is on the datasheet. A good check on distance measurements is to first tape in metric units, then tape in English units, and then use a calculator to convert and compare. There are 3.280833333 U.S. Survey Feet in one meter.

O. PHOTOS - Clean the marks off completely and photograph the marks. Ensure adequate and even lighting. Close-up photos should be in sharp focus, and clearly and legibly show ALL the information cast into, and stamped onto, the disks. Also take photo(s) showing the surrounding area.


1. Ask local residents for information, and permission, as necessary.

2. Once close to the triangulation station, go to the location where you would set a mark, where it would make sense (highest point, point with best view, exposed bedrock, etc.).

3. Marks originally positioned with GPS can be anywhere with good access and good sky visibility.

4. RMs are usually within 30 meters of the Triangulation Station, about the same elevation when possible, numbered clockwise from north, and about 90 degrees apart (around the Triangulation Station).

5. Older Bench Marks (vertical control points) are usually along a road or railroad, often set in a rock outcrop or bridge abutment. Newer, rod-type marks may be near the right-of-way fence along a road.

6. There may be signs of a previous survey, like old wooden boards or wire. In the Western U.S. some intact 4-foot wooden stands many years old have been found.

7. Ensure that the coordinates, map, and imagery are on the same datum (use NAD 83).

10. From the Description, determine if the Azimuth Mark is along the route to the main mark, and while enroute to the main station, watch for the mark and a possible Witness Post.

11. If the marks are still not found, consider using a metal detector and/or steel tile probe (long rod with handle).

12. Also consider construction in the area which may have destroyed the mark, or at least changed its setting considerably.


Below is a quote providing instructions for recovery of survey marks that is from USC&GS Special Publication #225, from 1959, pp 81-83:



One of the duties of the reconnaissance engineer is to recover existing stations to which to connect his work. These are frequently stations of early surveys marked in a variety of ways and the descriptions may be inadequate or out-of-date. If the original marks are visible, people in the locality can usually point them out. If the surface indications are gone, the recovery often requires much patience and labor. Triangulation stations are ordinarily placed on high ground and in a country of definite relief the highest hill will usually be the site, the immediate vicinity of which can be located from the original description. If the type of soil permits, systematic sounding with a prodding bar may locate the subsurface mark or fragments of the surface mark. When reference and witness marks are noted in the descriptions, some trace of them may be found even for very old stations. A large tree noted in the original description may sometimes be evidenced by a rotting stump or log or by discolored soil. Old signal foundations may be indicated by slight depressions in the surface, by softness of the subsoil, or by penetration of top soil into the subsoil. No digging should be done until all surface indications have been studied. Digging for a subsurface mark over a large area is a large task and there may be objections by the landowner.


Sometimes directions to tanks, chimneys, windmills, church spires, etc., which were observed when the station was established, can be duplicated by trial at the site and a close approximation to the station position thus found. Several subsurface marks have been recovered by the writer by this method after all surface indications had disappeared. In one instance, the directions on four church spires 6 to 15 miles away were duplicated with a 4-inch theodolite and the subsurface mark was found within 18 inches of the point thus determined. If solar observations are used to obtain the azimuths of the lines, it is possible to use this method when only two distant objects are visible. If a reference mark can be found, not too far from the station, the distance can be taped and the direction determined by magnetic compass. If the distance is fairly large, it can be determined by measuring a short base and two angles as explained on page 50 and the direction can be obtained by a solar observation. Many old stations were marked with tiles or pottery of various forms. If these marks have been broken, fragments of the materials remain in the top soil almost indefinitely and are of much aid in the recovery of the station. At many old stations broken tile, glass, charcoal, ashes, or other foreign substance was mixed with the soil at the station site. This was an excellent practice and should be revived.


Any digging required to locate a station should be done with care. The subsurface marks at old stations are usually small and fragile, and can be easily broken or displaced by careless digging. For this reason, some experienced man should do the work. Dirt of one depth of the shovel should first be removed and the new surface inspected for foreign materials, voids, soft spots, and discoloration. An old excavation below plow depth will remain soft in most soils for many years, and topsoil penetration into the subsoil is a sure sign of previous disturbance. Such indications will often localize the digging at once. If it be necessary to go deeper, another layer is taken off and investigated in the same manner. Each shovel full of earth should be broken up to see if it contains any fragments or other evidence of the mark. Signs will often be found which will make it unnecessary to excavate the entire area under investigation to the full depth. If there are many rocks in the soil it is necessary to inspect each one before removing it to avoid accidentally destroying the subsurface mark. Sometimes, a little investigation with a knife blade and whisk broom will save a great amount of digging. Some knowledge of the methods used by the party that established the station will greatly aid the reconnaissance engineer and it is also useful to learn if possible how the station was destroyed. The loss of surface markings may be due to local developments, to a fill over the original surface, or to a thorough destruction by vandals.


Cases arise in which it is impossible to recover a station with any reasonable expenditure of effort on the part of the reconnaissance party. It is then permissible to call for a test station in the immediate vicinity of the lost mark. If it appears probable that the subsurface mark may still be in place, the position of the test station may be determined by the triangulation party from the nearest recoverable stations and the distance and direction from the test station to the old station may be found by an inverse computation. The station can almost always be recovered in this manner if there are any remnants at all of the original marks.


A regular reconnaissance description should be written for each recovered station, including a statement regarding the condition of recovered marks, a note covering any irregularities or displacement of the mark, and a recommendation for re-marking if that is necessary. A recovery card should be submitted for every established station visited even though it is not used in the proposed scheme.”




“The description should be clear, concise, and complete. It should enable one to go with certainty to the immediate vicinity of the mark, and by the measured distances to reference points and the description of the character of the mark it should inform the searcher of the exact location of the mark and make its identification certain. It should include only essential details of a permanent character.”


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A couple of thoughts:


-Small loppers are often useful for clearing brush around a mark or for cutting roots away to enable digging. A very sharp trowel (the kind used to plant bulbs) will often succeed in making a neat, deep hole over a mark. This is particularly useful if you're working (with permission) in a landscaped area, or a lawn.


-Flagging (florescent plastic ribbon) is often useful to mark turns in a trail or the locations of marks not otherwise visible through heavy woods or brush. The flagging can be sighted on to check azimuths. Pick up the flagging when you are finished.


-A round-headed nylon brush (the type used to clean grime off of dishes) will often work to clean a mark where a larger whisk broom will not fit. These are also available with wire bristles, which may be better for cleaning older marks (but be careful not to leave permanent scratches on the mark).


-If old reference points (trees, buildings) have been lost, consider finding new ones and reporting them and their bearings/distances to or from the station. This may make the job of the next person who comes hunting the station much easier. Trees, fire hydrants, house corners, signposts, etc, are more permanent and make good reference points.

Edited by pgrig

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My additions to the equipment list are a distance wheel, (handy when the mark is 269 feet east of the center line of a intersection) and a Class II reflective vest for roadside work. To me a metal detector is NOT an option, but a must have.

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A metal detector must be able to locate non-ferrous metals for this application, and a magnetic locator will not work unless someone has added iron beside the benchmark.

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A metal detector must be able to locate non-ferrous metals for this application, and a magnetic locator will not work unless someone has added iron beside the benchmark.


Mine will pick up EVERY pop top pulled off and thrown away since 1965. :rolleyes:

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I just completed a "cookbook" of instructions for recovering a survey mark for a work project. I consulted several sources, including the Geocaching "Frequently Asked Questions". See what you think.


At many old stations broken tile, glass, charcoal, ashes, or other foreign substance was mixed with the soil at the station site. This was an excellent practice and should be revived.


I hope this is intended for the professional surveyors and not the recreational benchmark hunter. If it is intended for everyone, I will have to bow out. Thanks, but NO thanks. If it is intended for the professional why was it posted here?


As to the quote above and your thinking it should be revived, think twice if any lawyer sees that, you will be the prime target of a "reckless behavior & endangerment" lawsuit.


If a new description is written, it has to be verified by 2 other people?


Should this thread have been posted to the NGS forum instead of this forum where it will encourage too many newbies to start logging recoveries to the NGS way before they are ready? Problem have already been brought to light about faulty logs being made to the NGS by people who are not ready to make those type of logs.



Edited by 2oldfarts (the rockhounders)

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Excellent cookbook!


I suggest that your cookbook address the various issues of units of distance measurement.


Box score distances are in meters.

To-reach and the rest of the verbal instructions are in feet-and-tenths.

The person doing the recovery might have a tape in meters, feet-and-tenths, or feet-and-inches.

So, in any case, some kind of distance conversions must be done, at least for triangulation stations.


In my opinion, all datasheet distances, including box score distances if any, should be converted to whatever units the recovery person's tape has BEFORE going out into the field. That would put this in the area of your steps B and C. All computed positions and plots (sections D and E) should be made in the tape's units. Doing all these conversions at a desk and computer before setting out will greatly reduce error and frustration at the site.


The same as above is true of all compass bearings. All datasheet and box score bearings should be converted to magnetic before going outside by using the proper declination, unless this can be done by some automated equipment means (my old Suunto won't do that).


After returning from the recovery expedition, convert any new observed data to datasheet norms (feet-and-inches to feet-and-tenths (or meters), magnetic to true). That would be around step P.


In the photos section, you might want to be more specific. One aspect to be specific about is the kind of photo from a short distance with the mark clearly in the view or at least with its position clearly indicated. A look in the benchmark gallery will often show some pictures "from the station", which are of no to-reach use. Looking at the benchmark gallery will also show a bunch of disk-plus-GPSr pictures. I don't know if you want to address that touchy subject. Certainly loads of "view from" and "with GPSr" pictures can be uploaded, but they shouldn't be at the expense of "pictures with" and getting a better closeup of just the mark. I realize that looking at the benchmark gallery is not exactly the same as looking at a group of photos submitted to the NGS but it does show some current practices.


To convert from meters to feet, multiplying meters by 39.37 and then dividing by 12 is ultimately more accurate than 3.280833333 and is perhaps easier to do.

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I hope this is intended for the professional surveyors and not the recreational benchmark hunter.


LOL! I see where you're coming from, John. The instruction book might be thicker than the stack of data sheets one is carrying. :rolleyes:


However, George's tips and techniques will be of considerable value to the following sub-groups within our hobby:


*Those who submit updates to the NGS database;


*Those "never-say-die" types who will not leave a site without finding EVERY reference mark. (If your spouse frequently has to call your cell phone to remind you to pack it in and come home at dark, you MAY be one of these.)


If you fall into BOTH groups, you may need a laminated copy of George's Cookbook so you don't wear out the pages. While I'm having mine done, it probably won't be very expensive to make extra copies for a few others in the Forum. You can order from our special website, www.ThatDarnMarkHasToBeHereSomewhere.com


My only recommendation, George, would be to define the "white powder" used to dust the monument for better photography. There are some folks here who came of age in the 60's, 70's, and 80's. But then, with Street Value being so high, perhaps it is unnecessary to suggest using common household substances (such as baby powder or corn starch), rather than that substance you are carrying for "medicinal" purposes. B)



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It has also been suggested (and debated) that you should only carry white powders in their original manufacturer's package in order to reduce the risk of confusion with other substances by law enforcement people.

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Thanks George,


Great, concise instructions and tips all in one place. Wish that I had had them a few years ago when I did my first recoveries while working for a state agency.


I think that all of us playing this game should strive to become a proficient NGS submitter. Something like every student pilot should strive to learn and progress towards a Commercial rating, or maybe even an ATP.


I don't always carry my 200 foot tape (decimal feet & inches) with me on long hikes to a station, but I will have my pace stick - a fairly straight willow cut to my pace (5.5 feet) with foot and half foot intervals marked. Works good for snake avoidance also - saw just one all season long. Have used the GPSr calculator page frequently for the M39.37/12 conversion. kayakbird

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Thanks for all the positive comments and helpful suggestions. None of the content is intended to set a requirement, but rather to help find survey marks.


I will attempt to answer some of the comments/questions:


Pgrig – Good ideas.


2Jeeps2Jacks – Good ideas, but more equipment to lug around. I never had a distance wheel to use. Instead, I practiced and practiced my pacing. You can do this by laying out 100, 200, or 300 or more feet on level ground and walk it multiple times, trying hard to keep to your “normal” pace. Then average your results and come up with a simple formula to convert paces to feet. I still remember mine: divide the distance in feet by 3 and add 10% of the result. So, if I wanted 100 feet I would pace 33.3 paces plus 3 paces or a total of 36.3 paces.


Reflective vest definitely a good idea along a road.


I have never used a metal detector to search for a survey disk. I imagine it would be very helpful for difficult stations, but again, more equipment to carry.


Bill93 – Some USC&GS/NGS marks had a magnetic or rebar imbedded in the concrete, but most don’t.


2oldfarts – It was written for my work (read professional surveyors), but amateurs can use whichever parts are helpful. Regarding the broken tile, etc, that quote is from a 50-year old reference and was intended to provide a possible clue and to explain how it used to be done, not how it should be done now. Same comment on the “verified by 2 other people” – that was written 50 years ago and was not meant to set a present day requirement.


Black Dog Trackers – Good ideas on distance and angle conversions, I will add something.


On the photos, I’m with you. I don’t understand why people cover up a portion of the survey mark with their GPSr.


On the metric conversion, I memorized 3.280833333 over 30 years ago and still remember it. Also, there is little chance of applying it backwards. Remember, this is the conversion for the U.S. Survey Foot. The conversion is slightly different for the International Foot, which some states use. For more information on the two definitions, see: http://www.ngs.noaa.gov/PUBS_LIB/ManualNOSNGS5.pdf , page 11-12.


PFF – Good idea, I will add a comment about what the “white powder” is!





P.S. Watch for my survey mark quiz, almost ready for release.

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Many of the more serious benchmark hunters will be thankful for your cookbook. Some of the newbies may be amazed by so much information, but it would be nice to have fewer "false destruction" reports and incorrect "found" reports.

Thanks for your efforts.



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As for the white powder I’ve been thinking of using red, yellow or blue powder for chalk lines as well as the white baby powder. It might come in handy on marks like TU0641



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If you fall into BOTH groups, you may need a laminated copy of George's Cookbook so you don't wear out the pages. While I'm having mine done, it probably won't be very expensive to make extra copies for a few others in the Forum. You can order from our special website, www.ThatDarnMarkHasToBeHereSomewhere.com




You didn't get the correct URL Here is the link. www.ThatDarnMarkHasToBeHereSomewhere.com



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Thanks...I'll find the Cookbook to be very useful. Its contents will help me to become the qualified benchmark hunter that the activity demands.

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