Duh! Benchmark/stamping Meaning

[+twm3]

Duh, though I've recovered 50+ benchmarks, a probably obvious question has come up. Does the cross in the middle of the benchmark have directional significance, i.e. does an axis point to true north? If so, which one?

 

The benchmarks I found yesterday, and probably in the past, have writing on them that is "right side up" going from the 9 to 3 o'clock position across both the top and the bottom. In the middle of the benchmark, there is a cross-hatch with a long axis running from 9 to 3 and a shorter hatch running from 12 to 6 o'clock. Do any of these axis point to north. If so, which one?

 

Yup, my face is a bit red here. When I was out benchmarking yesterday, I forgot to note the orientation of the benchmark and then began to wonder if the benchmarks would have this information.

 

~twm3 and Cayenne, The Clueless, Hyperactive Non-Geocaching Dog

[2oldfarts (the rockhounders)]

My best guess is that mark you're referring to is for the position used to measure the elevation of that disk.

 

We have seen them oriented different directions. Usually when we find one near a roadway right-of-way fence, the line on the disk is parallel to the fence. And we have found them along many different roads going different directions.

 

Hope this helps until a real surveyor comes on-line and answers.

 

John

[evenfall]

Hi twm-3,

 

As John said, that symbol is the location where the measurement is taken.

 

There have been varying schemes used for discs down through the last century and there have been a number of agencies who use them. As a rule of thumb, If the disc was placed in the ground by an agency which has had two names; US Coast & Geodetic Survey, or National Geodetic Survey, then there were a few basic designs for the center of the disc. It is important to note that the agency who's database we use to help us find these survey marks with belongs to the National Geodetic Survey. I will refer you both of these as the NGS from here on.

 

First the Bench Mark. Now on the disc it self it will have the words, Bench Mark. 2 words, not one like we use commonly here at geocaching, and it will mean to a geodesist or a surveyor that this disc represents a type of survey data which originally represented elevations, or what we call vertical control. It usually will have a Plus + or a cross hatch with the vertical line is shorter than the horizontal one. On the older discs the horizontal line is extended to the edges of the disc. On a Bench Mark, a survey instrument is physically rested on the disc to take the measurement and always taken from the center of the disc. There are variations on the theme of designs of course but this + is the symbol most frequently used for Bench Marks, or vertical control.

 

On Horizontal Control, sometimes we will see the words "Triangulation Station" on the older stations, and the words "Horizontal Control Mark" on the newer ones. On these, if they were originally meant to be for horizontal control as a primary purpose there was a Triangle with a Dot in the middle of them as a symbol, and this was meant to signify the location from where the survey data was measured, however, on these stations, we usually do not have to touch the Horizontal Control. The triangle and dot are targets for instrument to be centered over. There were a couple other designs used by the NGS over the years for Magnetic and Gravity stations and they used different symbols than the triangle, but they were considered horizontal control.

 

Probably the third most common disc you will see is the USGS Bench Mark... The USGS did their design a bit different than the NGS did. It is a Triangle with a + inside it and yes, it its used for both Horizontal and Vertical survey work.

 

There are many other kinds of discs placed by many agencies, but most are similar to these designs and for the most part, the center of the disc is the place where the data is significant.

 

As to the orientation of the disc? No, I have never known of any particular alignment, and of the I don't know how many I have used in my career, I can see no pattern, nor remember one. Most commonly it seems to me, most were oriented facing the direction that one would be considered most likely to approach it, and that isn't always true either. Noting the direction the mark is oriented in your field notes is not required.

 

Just for familiarity's sake, here is a link to a look at some of the discs you will encounter in the field. http://www.dustyjacket.com/benchmarks.html

 

Enjoy and hope that helps!

 

Rob

[+twm3]

Hiya Evenfall,

 

Thank for the informed (? :-) opinion and/or fact regarding orientation.

 

GC sez that I've attempted close to a 100 benchmarks and have found about half of them. I've considered our benchmarking venture as adding to the knowledge base on the web. In particular, by following our comments and photos (thank gahd for digital cameras :-), folks in the future will be able to find the benchmark faster than I did.

 

To that end, I've tried shooting N, E, S, & W from the benchmark. In my last trip out into the field, I forgot to note my orientation when shooting the quadrants. But wait, maybe I can save my bacon if the "+" has orientation information built into it. Alas, it doesn't appear so which means that I will be entering my photos as views from the benchmark versus "Northerly view" from the benchmark.

 

Thanks again for your help.

 

~twm3 and Cayenne, The Clueless, Hyperactive Non-Geocaching Dog

[Bill93]

While pictures FROM the mark provide useful information, it is generally considered better to take pictures showing the location OF the mark in relation to objects that someone can recognize in the future. It can be hard to find the right place to stand so that you see what is in the picture looking away from the mark.

 

I see that you actually did this to some extent so that you see the benchmark location in some of the pictures of KS0176, and this is good. I might have stepped back a little further for some.

 

BH

[evenfall]

twm3,

 

Based on my career in the Survey field, Yup. More than an opinion, it is an informed observation based over years of experience. I cant say I have ever seen a disc monumentation which was purposefully oriented to face any specific way. I also say that, based on training and knowledge of NGS and other surveying methodologies. I have never read anywhere that advised the placement and orientation of the disc be oriented to face any specific way. Those are just place markers. The instruments we use determine the angles and directions from place to place.

 

Hope that helps.

 

Rob

Edited September 6, 2005 by evenfall