Intersection Stations + NGS markers

[dadunkindude]

Call it a n00b question, but I noticed that a water tower near my work is listed as an NGS benchmark. So I walked over there today to try and verify the presence of the marker. I circled the whole thing multiple times and could not find any sign of the metal benchmark, either on the support legs of the water tower, or the center pipe. I know it is the same water tower since it has been there forever even though the color scheme is different than the datasheet describes. So I got to wondering, are objects like water towers and radio antennas given benchmark discs to find or is the object itself considered the "benchmark?"

 

Specifically, the marker in question is http://www.geocaching.com/mark/details.aspx?PID=OZ1054

[Wintertime]

"AN ELEVATED WATER TANK, PAINTED IN RED AND WHITE CHECKER BOARD FASHION"

 

That's the surveyed location, and as you noted in your subject line, it's called an intersection station. There is no "benchmark" in the sense of a metal disk.

 

Patty

[+LSUFan]

Welcome to benchmarking. A good place to start is the FAQ section:

 

http://www.geocaching.com/mark/default.aspx

 

where an intersection is explained:

 

Intersection Stations (a Type of Horizontal Control)

An intersection station is a prominent landmark, such as a water tower, radio tower, church spire, mountain top, or any other type of object that can be observed from a distance. These kinds of "large object" station markers, known as intersection stations because of the way their coordinates are calculated are usually landmarks higher in the air than any surrounding objects, which allows them to be seen from many miles away in several directions. By observing one or more such points through a telescope, surveyors can determine positions on the surface of the Earth through the use of trigonometry.

 

Intersection Stations

Intersection stations are surprisingly tricky. Be sure to read the entire datasheet carefully. Pay particular attention to the first date the structure was reported or established as a survey mark (usually listed as the date "First Observed"). The structure you find must be one that you're certain existed and appeared the same way as it did on that date. If the structure was re-built then the station is effectively destroyed since the re-built version of the structure might be in a slightly different position. If you're uncertain about what happened during the time between when the structure was first monumented (observed) and the present, check with the structure's building manager. Since all intersection stations have adjusted coordinates, they must be at the published coordinates. If there is no such marker at the published coordinates, then the mark should be considered destroyed. If you find a structure that seems to be the correct one, but your GPS indicates that the position is incorrect, you have not found the correct mark.

If the intersection station is a water tower, read the datasheet carefully to note the details of the description of the water tower, and the first date the water tower was reported or established as a survey mark. For example, the datasheet says the water tower has 4 legs, has a cone shaped top, and was monumented in 1931.

 

* If you found a water tower that has 6 legs or just one leg (a standpipe), then the water tower station has been replaced, and the water tower station described is destroyed.

* If you found a water tower that looks newer than one built in 1931, then the water tower station has been replaced, and the water tower station described is destroyed.

* If you found a water tower that has 5 legs and a round top, then the water tower station has been replaced, and the water tower station described is destroyed.

* If you have found a water tower that is in the wrong coordinates, then it is not the correct water tower, even if it is what was described in the datasheet, because all water tower stations are location adjusted and cannot be at the wrong coordinates. You should go to the position of the datasheet's coordinates as indicated by your GPS receiver. If the correct water tower is not there, then the station is destroyed.

Edited January 18, 2012 by LSUFan

[dadunkindude]

Welcome to benchmarking. A good place to start is the FAQ section:

 

http://www.geocaching.com/mark/default.aspx

 

where an intersection is explained:

 

Intersection Stations (a Type of Horizontal Control)

An intersection station is a prominent landmark, such as a water tower, radio tower, church spire, mountain top, or any other type of object that can be observed from a distance. These kinds of "large object" station markers, known as intersection stations because of the way their coordinates are calculated are usually landmarks higher in the air than any surrounding objects, which allows them to be seen from many miles away in several directions. By observing one or more such points through a telescope, surveyors can determine positions on the surface of the Earth through the use of trigonometry.

 

Thanks for the guide, but even after reading it I wasn't sure if the NGS marked their intersection stations with a disc or not, because the guide states "If there is no such marker at the published coordinates, then the mark should be considered destroyed." In my mind, that meant perhaps a marker (disc) should be at the location of the tower because it still stands. Though I guess it makes sense that if the object disappears, it can no longer be used as a point of reference, which is why they wouldn't leave a disc.

[kayakbird]

However; some intersections

 

 

CHINOOK MUNICIPAL TANK

 

have very close by disks.

 

 

CHINOOK

 

Which very seldom get the consideration shown this one (sure hope that the photo enlargement does happen tomorrow). kayakbird

[+LSUFan]

 

Intersection Stations (a Type of Horizontal Control)

An intersection station is a prominent landmark, such as a water tower, radio tower, church spire, mountain top, or any other type of object that can be observed from a distance. These kinds of "large object" station markers, known as intersection stations

 

Thanks for the guide, but even after reading it I wasn't sure if the NGS marked their intersection stations with a disc or not, because the guide states "If there is no such marker at the published coordinates, then the mark should be considered destroyed." In my mind, that meant perhaps a marker (disc) should be at the location of the tower because it still stands. Though I guess it makes sense that if the object disappears, it can no longer be used as a point of reference, which is why they wouldn't leave a disc.

 

OK, I can see where someone might confuse the terminology of what a mark is. A disk can be a mark......but you need to remember a mark doesn't have to be a disk.

 

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.

 

Vertical Control Marks

These are the true "bench marks". Generally the words BENCH MARK will be printed on them near their rim if the mark is the disk type. Many vertical control marks are not the disk type, however, and can include bolts, rivets, chiseled squares, chiseled crosses, etc.

 

Horizontal Control Marks

There are several types of horizontal control marks. They differ by which kind of horizontal control system was used in establishing them and the amount of precision they represent. Most horizontal control marks are marked with a disk, but some are other types such as a chiseled cross, bolt, drill hole, etc.

 

Intersection Stations (a Type of Horizontal Control)

An intersection station is a prominent landmark, such as a water tower, radio tower, church spire, mountain top, or any other type of object that can be observed from a distance. These kinds of "large object" station markers, known as intersection stations

 

Now that you are becoming a curious benchmarker like the rest of us-- George Leigh with the NOAA has a fantastic article named "Bottles, Pots, and Pans: Marking the Surveys of the U.S. Coast & Geodetic Survey and NOAA"-- A history of the evolution of marks used by the Survey under different names and at different times.

 

You might want to check it out along with some other things at:

 

http://www.ngs.noaa.gov/web/about_ngs/history/indexhUSCGS.shtml

Edited January 18, 2012 by LSUFan