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New Benchmarks?


arrowroot
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I've been seeing a number of rivets recently placed in sidewalks, parking lots, etc., surrounded by a pink spray-paint circle or triangle, and occasionally a code number.

 

Is there a new generation of benchmarks going in, or am I seeing general surveying going on in the Chicago area?

 

I am Arrowroot, son of Arrowshirt. I have many names, you know

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quote:
Originally posted by Kewaneh & Shark:

Discussion and an explanation about Photogrammetric Aerial Control points


OK, that clarifies it. Thanks much.

I take it from the explanation that the points are established at random, well, not exactly. They just are not at an established BM.

In this particular case, it makes good sense. There are several hundred acres of gold tailings here in town and a developer is looking at cost for making it environment safe and possibly building a new baseball stadium. I see these markers scattered around the site and in local neighborhoods.

 

1950 Surveyor

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When we placed aerial panels out at the DOT, they supplied us with a USGS maps with the locations of where they wanted panels placed. We would place them it the most ideal location for our use and to make sure no obstructions would hide the panel. We had to pay attention to shadows from large buildings and trees that could make interpreting the photo difficult. It took a skill to lay out the panels so that they would be useful. We did not know where the planned to fly, as they often overflew areas to get the coverage.

 

Our normal mapping flights used Targets 8 ft in overall length, high altitude flights use targets at 16 ft. These were used for route location studies where a greater area was needed and no precise ground mapping was going to be done.

 

They are different versions of aerial targets. We used 8" wide x 8 ft long while vinyl laid over cheap black vinyl mat to highlight the white. In 30 yrs we also had one project done in color, most all is black and white photos. The color was a lake erosion project where the wanted to see if they could see the lake bottom along the shoreline. Many of our projects were rural, we often had to search long and hard for open areas to place the targets. We even would clear an area if need be with permission of the owner which no one ever refused.

 

Also, we used to paint just 8 ft dash across the centerline at specific intervals, (1000 ft) and they would use this for what was called "Photo-Plans" where the superimposed the photos to scale on a set of plans and used this for road improvements. This was mainly used for safelt improvements, drainage work etc where precise detail and elevation was not necessary.

 

Probably more then you ever needed to know.

 

Mike

Survey Tech (Retired)

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quote:
Originally posted by elcamino:

They are different versions of aerial targets. We used 8" wide x 8 ft long while vinyl laid over cheap black vinyl mat to highlight the white...


Oh, I have a picture of one of these, 42376_100.jpg , it sure puzzled me at the time. This one was centered right on a BM.

BTW the location has an unlikely story about it - if you've got few minutes to spare, read VacMan's thread in Trash Out board on the Cache Which Went to Jail.

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Those are both good examples of aerial targets and probably the two most popular methods used for creating them. MOCKBA's example is for lower altitude flights and BeachBum22's is obviously sized for a higher altitude flight.

 

Surveyors would have measured the horizontal and possibly vertical positions of the benchmark and traverse point so the photogrammetrist would have common control points between the photo images. The crosses are so the photogrammetrist can see those tiny points from the air.

 

Keep on Caching! (and Benchmarking!)

- Kewaneh

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quote:
There are several hundred acres of gold tailings here in town and a developer is looking at cost for making it environment safe and possibly building a new baseball stadium. I see these markers scattered around the site and in local neighborhoods.

 

Papa,

 

This is off the topic, but I shake my head when the City of Colorado Springs makes the Developer of that site fight an uphill battle because those tailings are filled with "dangerous" chemicals, etc.

 

If the City thinks they are so dangerous, why have those tailings been allowed to erode into Fountain Creek for the last 50+ years? Why were they used for fill at the Penrose Equestrian Center?

 

It seems to me that the City looked the other way until someone with deep pockets came along to fix the problem.

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