triangulation station disk

[+Wabbits]

I did a search and trying to figure out what I'll be looking for. I couldn't find anything. There seem to be quite a few in my area with missing or destroyed "peices".

 

example

 

R.M. 1 - solid

R.M. 2 - damaged

AZIMUTH MARK DISK - destroyed/missing

 

and I basically looking for three benchmarks in a triangle shape spread out over the ground?

 

thanks

 

btw I think finding discs no one has found for over 20-40 years is more enjoyable that one found 5 years ago. Kinda like a FTF.

Edited April 30, 2007 by Wabbits

[mloser]

The fact that most tri-stations are set with three disks is pretty much a coincidence. The term triangulation comes from the use of triangles over a large area for geodetic surveys--determining the shape of the earth. A survey party would "occupy", which means they would set up equipment directly above a triangulation station, then they would measure the angles to other distant triangulation stations. Doing this repeatedly would result in a string of triangles. Imagine you have a triangle of points A, B and C. If you measure the angle from A to B and then A to C, and you know where A is, then you can tell where, along a line, B and C are. If you measure from B to A and B to C, you can determine where B and C are. By measuring back from C to A and C to B you can check your angles. Imagine doing this along a line of marks hundreds of miles long. That is what tri-stations are (were!) used for. Here is a map of a triangulation survey in Colorado which may show you better what I am talking about. Understand that each line on the map was measured in both directions, from point "A" to "B" and "B" to "A", and the math checked, before the survey continued. Survey parties often spent weeks at a marker before the weather and conditions were right for sightings.

 

Now on to the three marks: For each triangulation station there is a main disk (the station) and normally 2 reference marks.

 

The reference marks are used to help find the main disk. Each is set at a carefully measured distance and angle from the main station. Thus you have 3 things to look for instead of one. If one gets destroyed the hope is that others will remain.

 

However, only the MAIN station counts--it is the one the measurements are made from. If it is destroyed the station is not usable unless it can be recreated. This is more possible than it may sound--many tri-stations have an "underground mark", which is set directly below the main mark, in a concrete slab. The main mark is then set in a concrete monument above that mark. The depth of the underground mark is often noted on the datasheet, but is typically 3 feet or so. If the surface mark is gone but the reference marks remain, they can be used to locate the underground mark, which can then be used for the survey, and/or a new mark set above it.

 

That is the theory. In practice, and with GPS being so easily available, it is doubtful anyone takes the time to dig out an underground mark, and I haven't heard of anyone setting triangulation stations recently.

 

The disks are sometimes set in a triangle, sometimes in a line. The actual directions seem to be of little consideration. I would say that overall I have seen them more close to linear than triangular. The distances are also random. My memory says that I read something about them being about 100 feet from the mark, but in practice I have seen them anywhere from 8 feet to 300. Eight feet is a bit close--whatever would destroy the station may well destroy the reference marks too. 300 is way too bit long--it is very hard to measure that sort of distance. Forty to 75 feet seems to be the norm.

 

Finding information on the reference marks is easy if you get the NGS datasheet. Amidst all the jargon and numbers is what is called the "box score" which tells you how far and at what angle each of the reference marks is located.

KW3135|---------------------------------------------------------------------|

KW3135|.PID....Reference Object.....................Distance......Geod. Az..|

KW3135|...........................................................dddmmss.s.|

KW3135|........BAILEY RM 1...........................8.808 METERS 12508.....|

KW3135|.KW3125 MARYSVILLE..........................APPROX. 6.3 KM 1850437.9.|

KW3135|........BAILEY RM 2..........................22.185 METERS 21109.....|

KW3135|---------------------------------------------------------------------|

 

Ignoring the periods in this box (I had to put them there to space it correctly), the box shows exactly where BAILEY RM 1 and RM 2 are located. RM 1 is 8.808 meters at 125 degrees 08 minutes from the station. If you find RM 1 you can turn this around and measure back to the station.

 

Hopefully that will give you something to go on. Others here will chime in with other tips and tricks.

 

I think you should go after BZ1342 first. Nothing like a station with a description that reads, in part: THE AREA IS HEAVILY LADEN WITH UNEXPLODED ARTILLERY ROUNDS. And I thought poison ivy was a deterent!

[+Klemmer]

BUT: In this hobby / sport, there are LOADS of exceptions. That keeps it interesting! DX4739 (TAFT) is a triangulation station I looked for recently, with a Reference Mark (RM 3) almost 0.4 mile from the main station mark! No help at all in locating the station. In this case, I believe that it is mean to serve as an Azimuth disk, wich are normally set a good distance away from a triangulation station, in order to provide a good long "baseline" for other angular measurements. I guess they didn't have an azimuth disc that day.

[+2oldfarts (the rockhounders)]

I would like to add that location is 'adjusted' on (most? or all?) triangulation stations, so your GPSr should take you right to the station disk.

 

Also please note that the station disk is denoted by a triangle on the disk.

 

HOLES

 

The RMs will have arrows on them, usually, unless they have used marks already in the area (we have seen section markers - GLO and pipe caps).

 

 

I agree with you that First To Recover on old marks are the best!

 

Shirley~

[mloser]

Server error made me post this a bunch of times!

Edited April 30, 2007 by mloser

[mloser]

I think all tri-stations are adjusted. It is the nature of the beast--since they are used for horizontal control they have precise coordinates.

 

And your GPSr WILL take you to the precise location, up to the accuracy of the unit (9 feet according to my Garmin documentation), the satellite constellation at that time, and the amount of sky visible to your unit. Not all marks will be as obvious as 2oldfarts' example either, standing proud on a rock outcrop. In my area they are often under leaf cover or dirt. KW3135, which I found yesterday, was under a fallen tree and two rocks. Since I was under leafless tree cover my accuracy at that point was about 20 feet, so without the description, a reference mark, and my metal detector I would never have found it.

 

Klemmer, it is the exceptions that make the rule, so they say, and explaining every exception would probably mean the every tri-station I found would have a separate how-to!

 

I also love the not found marks, and the older ones. Finding a piece of history from the late 1800s or the early part of the 20th century is what makes this hobby fun for me.

[mloser]

Server error made me post this a bunch of times!

Edited April 30, 2007 by mloser

[mloser]

Server error made me post this a bunch of times!

Edited April 30, 2007 by mloser

[mloser]

Server error made me post this a bunch of times!

Edited April 30, 2007 by mloser

[+2oldfarts (the rockhounders)]

Not all of our finds are in the wide open spaces. Check out the hiding spot for RM 2 on This one! We do have some challenges now and then.

 

 

 

John

[+Harry Dolphin]

And sometimes, the triangulation station is buried eight inches below the lawn of the local day care center.

2oldfarts made me do it!

[Z15]

marks with Presidents names of them, cool

 

only 41 left to find

 

Edited April 30, 2007 by Z15

[+A tapeworm]

...

Finding information on the reference marks is easy if you get the NGS datasheet. Amidst all the jargon and numbers is what is called the "box score" which tells you how far and at what angle each of the reference marks is located.

...

 

 

Are there other ways to use azimuth in this situation? Specifically, I've been befuddled by OK0603 :

 

Documented History (by the NGS)

1/1/1931 by CGS (MONUMENTED)

... STATION IS 10 METERS (33 FEET) SOUTH OF CENTER LINE OF ROAD ... REFERENCE MARKS ARE STANDARD REFERENCE DISKS IN CONCRETE, NOTE 11A. NO. 1 IS ON NORTH SIDE OF ROAD, 2 METERS (7 FEET) SOUTH OF FENCE LINE, 18 METERS (59 FEET) WEST OF SOUTHEAST CORNER OF ORCHARD, AND APPROXIMATELY 100 METERS (328 FEET) FROM STATION IN AZIMUTH 259 DEG 20 MIN 05 SEC. NO. 2 IS ON NORTH SIDE OF ROAD, 3 METERS (10 FEET) EAST OF EAST END OF GATE LEADING TO RAMBLING HOUSE, 7 METERS (23 FEET) NORTH OF CENTER LINE OF ROAD, AND 22.11 METERS (72.5 FEET) FROM STATION IN AZIMUTH 147 DEG 31 MIN.

 

If the station is on the S side of a road running pretty much due E-W, how can following an azimuth of 259 deg (RM1) or 147 deg (RM2) bring one across to the N side? The mark referenced is now gone, but a few years ago it was indeed present on the S side (when I photographed it as an example while teaching topo map reading to Science Olympiad kids!)

[+Team Fawlty]

What you have found is the azimuth mark. The description is bit sketchy but per the 1969 recovery note, a new RM 2 and azimuth was set (maybe RM 1 in the box score since there is no distance for it) thus the stamping 'RANDALL AZIMUTH MARK 1969'. Standing at the azimuth mark, you should follow an azimuth of 281 40" to get to the station. RM 2 from 1969 should be north of the road and might still be there. Also, the 1992 desc appears to be a partial copy of the original desc. I agree, though, that 259 should put the RM WSW of the station, but, I believe the azimuths were measured from the RMs - mathmatically, the distances all seem to work.

 

From the current NGS sheet

 

STATION RECOVERY (2003)

OK0603

OK0603'RECOVERY NOTE BY INDIVIDUAL CONTRIBUTORS 2003 (KB)

OK0603'MARK REMOVED DURING EXCAVATION FOR A NEW DRIVEWAY IN AREA.

 

Brendan

Edited May 1, 2007 by Team Fawlty

[+2/3 Marine]

Mloser.

How did you ever come across the triangulation map of Colorado from 1881? There weren't many tri stations east of Pikes Peak back then. Very interesting to look at the map and see where the stations were/are.Have been waiting for some snow melt on the top of the Peak to go up and get the ones on top. Seems as though the original tri station from 1879 was replaced in 1953 JK1245. Always learning something new & interesting in the forum. Maybe I'll get some good 14,000' high pictures before the contest ends. The road to the top isn't open yet, hmmm! there's always the cog train.

[holograph]

How did you ever come across the triangulation map of Colorado from 1881? There weren't many tri stations east of Pikes Peak back then. Very interesting to look at the map and see where the stations were/are.

 

You can see about a dozen in Eastern Colorado from 1880-1881 at this page. Those will be some of the earliest ones in the NGS database. Any surveys done prior to that would probably be from Army surveys and wouldn't be in the NGS database.

[mloser]

2/3 Marine, I just did a search for Triangulation Maps and that one came up. It is on the David Rumsey map site. He collected old maps and has made them available on the web.

[Bill93]

It looks like we've got several conversations going intermixed here. Tapeworm asked:

 

>Are there other ways to use azimuth

 

Yes. At one time geodesists reckoned azimuth from south. If you look at the NGS data sheet for OK0603 you will see the box score has RM1 at 079 degrees but the old description called it the other way at 259.

OK0603................................................................................................dddmmss.s

OK0603..............RANDALL RM 1................................................................07920

OK0603.NF1610 DYGERT...............................................APPROX.18.1 KM 1685817.3

OK0603.NF1645 GRAND RAPIDS SILVER WATER TANK...APPROX.15.3 KM 2413640.6

OK0603..............RANDALL RM 2.......................................22.110 METERS 32731

OK0603---------------------------------------------------------------------