September 13, 2013 at 5:07 PM #295
This primer is for those geocachers who may also wish to try their hand at searching for benchmarks. Benchmarking is a little different from geocaching, but can be as much, if not more fun. If you have never noticed, you can do a search for nearby benchmarks from each geocache page. Logging a benchmark will not count toward your total geocache finds, however.
First off, just exactly what is a benchmark?
A benchmark is a point whose position is known to a high degree of accuracy and is normally marked in some way. The marker is often a metal disk made for this purpose, but it can also be a church spire, a radio tower, a mark chiseled into stone, or a metal rod driven into the ground. Over two centuries or so, many other objects of greater or lesser permanence have been used. Benchmarks can be found at various locations all over the United States. They are used by land surveyors, builders and engineers, map makers, and other professionals who need an accurate answer to the question, “Where?” Many of these markers are part of the geodetic control network (technically known as the National Spatial Reference System, or NSRS) created and maintained by NOAA’s National Geodetic Survey (NGS).
WARNING: Many benchmarks will be located on private property, including railroads. Make sure you obtain permission before you search for benchmarks on private property. DO NOT trespass to find a benchmark.
The above definition and much more information concerning benchmarks, especially about equipment which you may want to carry with you, can be found at gc.com’s benchmark page located below. You might want to scan it first.
OK, You’re now wanting to start looking for benchmarks. What should you do next?
First off, don’t totally depend on the gps coordinates listed. These numbers will usually get you to the area, but can be off by 600+ feet. You need to read the official description of the benchmark, which will give you exact measurements from road centers, buildings, fences, landmarks, witness posts, etc. A lot of these features may have changed over the years, and could possibly be gone alltogether (along with the benchmark). They may even be underground. That’s part of the fun in benchmarking, as you may have to do a little creative reconstruction in your mind if the items in the description have changed. A lot of the time, the road centers will in the same place, even if the road is widened.
Why aren’t the gps coordinates always accurate?
These benchmarks were placed out a long time before there was even anything called a gps. After the advent of the the global positioning system we now have, certain people sitting at desks, took a ruler to a topographic map and used their best guestimations for the coordinates. These estimations will get you in the area, but usually not to the benchmark. You will need to use the official descriptions.
How do I get the official descriptions of benchmarks?
There are a couple of ways to accomplish this. First off, you can get them from gc.com. You can do a search for nearby benchmarks from a geocaching page, and then go to each page. You can print these pages out or download them for paperless caching. Currently gc.com doesn’t have a way to run a pocket query for benchmarks, so it can be time consuming to download each individual benchmark page. Also, gc.com hasn’t updated their benchmark database in a long time, so the information there is many years old.
If you want more up-to-date information and the ability to download every benchmark in a parish( or county for those MS people) in one swoop, then here is an easy way to do that. Go to the National Geodetic Survey website’s datasheet page, located below.
Now you will
1. Click on “DATASHEETS” tab
2. Scroll down to the “COUNTY” tab
3. Scroll thru the states and highlight/click “LOUISIANA”, now click the “Get County List” tab
4. Scroll and highlight/click the parish/county you want. Make sure “pc zipped” is checked and click on “download file”
5. Save it to wherever you wish on your computer, and make sure you go back and unzip it, if your computer doesn’t automatically unzip for you.
Repeat the above for each parish/county you wish to download.
EDIT: Jim/Holograph has made this task easier. He maintains the benchmark datasheet state/county downloads (and updates) on his website. His datasheets will be more current than the NGS site because he updates his everytime that the NGS adds new recovery reports, instead of just their yearly archives.You can access them here:
Alright now we will need one more piece of software. The datasheets (in their .dat file format) we downloaded above will need to be converted to a gpx file, which most of our geocaching utilities (like GSAK) can understand….similar to a pocket query. This benchmark to gpx converter was written by a fellow geoacher and can be found at the following link:
You will need to save this zip file on your computer first. I saved it in the same file where I downloaded the parish benchmarks from the above steps. Once you unzip this file, you can easily do the conversions. I find it easy to keep all the benchmark downloaded files and the gpx converter all in the same folder.
Once it is unzipped, there will be a folder called BMGPX. Inside this folder, there is a readme file and another file called bmgpx, that has an icon, looking like a box with a blue bar at the top. This is what we will use to make the conversions.
All you have to do is drag one of the unzipped parish datasheet (.dat) files that we downloaded above, onto this bmgpx icon, and drop it there. The program will instantly do the conversion and a new file will appear with the same name, but will be a gpx file. You can now take this new gpx file and load it into GSAK, your gps (if it takes raw gpx files), EasyGPS, GPXSonar, etc.
EDIT: Since this tutorial was written several years ago, I have been made aware, and starting using other great GPX conversion utilities. They do even more things than BMGPX does. You can get them at
Hint: The datasheets are listed by numbers for the parishes/counties, and will have this number when you download them. Unless you can remember which number goes to which parish (073 is Ouachita Parish), then I suggest you rename the files to the parish name to help you, when you are wanting to look up the information.
SOMETHING KIND OF NEAT (if you want to be cool)
You can log the benchmarks on geocaching.com, but did you know that you can also report your searches directly to the NGS, and be a part of their official record? Well, you can.
The NGS realized what a valuable asset that geocachers were to them, and have made geocachers their own agency code to report the benchmarks. When you submit a report to them, you will use the geocacher agency code and your own initials. When they update their records (about 30 days), then your report will be part of the official record and listed as such.
The NGS asks that if information about a benchmark has been listed within the last 12 months, with no change in the status, to NOT report it to them. You will need to be familiar with the formats and protocols required by the NGS to submit reports, since these reports will be viewed by professionals. It is highly recommended that you gain a lot of experience with benchmarks before actually submitting reports directly to the NGS.
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