Yesterday and today there was a car parked in front of our school right next to a benchmark that had what appeared to be a GPS antennae as i looked like a plate turned upside down and on a tripod. There was also a ginat standard antenna next to it. Ive seen the plate and tripo around town on benchmarks but never the giant antenna. I tried to get apicture but it was gone when I came back with the camera. It was there for about 24 hours. What are they doing here?

Happy Hunting!
-Amazingracer

Black holes are where God divided by zero.

Was it a black SUV with black windows? - - -
ALIENS!


Well, that theory is as good as my theory for ~eriks~ new cache. (And probably closer to the facts)

Are your crazy?

It was men in black tracking aliens.

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Some of those that wander are lost!

[EDIT] Was thinking it might be a field intensity survey for an AM radio station, but they'd be there for minutes, not 24 hours. Maybe it was a survey base station. The big antenna might have been for a DGPS beacon receiver.

Scott

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Scott Johnson (ScottJ)

This is a gps base station. As you know you have several errors in a hand held gps unit. These errors can be minimised by differential gps work. I am not going to go over all the type of errors because it would take several pages and I think you want to know what time it is and not how to build a clock. This station is set up on a point of known position and elevation. It is receiving information that computes a position from outer space which is in error, however it compares this position to the known position and elevation thus determining a correction. The whip antenna you see is a fm transmitter which broadcasts the correction to a rover or several rovers. If the rovers and the base station are seeing the same constellation of satellites, then the rover can determine its true position in real time. Sometimes you do post processing which applies the correction to the data after the survey is complete and the transmitter is not necessary. The accuracy is a function of the length of the line between the two receivers, however in this case it is probably sub centimeter accuracy. Your waas is almost the same thing, but not in the ball park for accuracy because of the length of the base line and your hand held is not using all the information broadcast by the satellies.

There is a ton of information out there and I am finding out you can do sub meter accuracy with your hansheld, but it has to be connected to a windows ce device or a laptop and the software is very costly. Do a google search for rhino or earthmate.

I manage this type work on a daily basis. Get in touch with a local land surveyor and see if he will do a presentation for your math class. While you are at it, ask him about trig-star and how your students can compete and win scholarships. Try Donaldson Garrett Inc. in Macon at 478 474 5350

George White
Professional Land Surveyor
678 817 6092

George, you saying that it's a WAAS site? Where in Macoon is it located AG?

Nick T

It was located in front of our school off Foster Rd. over a benchmark. i have seen other fllat plate GPS antannes around town but the one at school was the first one with the FM antenna.

George, you saying that it's a WAAS site?

Absolutely not!
It is a control point of known position and elevation somewhat erroneously called a "benchmark" by geocachers.

It was set by surveyors to be used to establish other control points and to determine elevations and positions of points such as a property corner.

A "benchmark" is a point of known elevation.

Well dictionary.com seems to agree with us geocachers. It defines benchmark as

often bench mark A surveyor's mark made on a stationary object of previously determined position and elevation and used as a reference point in tidal observations and surveys.

So professional Surveyors like you may use a benchmark to only mean elevation and use the term control point for location. However it seems valid for the general public to use term benchmark for location.

Now us computer types, can use Benchmark to mean something totally different from location. To us a benchmark can be series of standard computer processes. When we compare computer systems, we run a "Benchmark" on each and see which one runs it the fastest.

Yes , and we blow our noses on Kleenex and not tissues, but it is all a matter of semantics. I am not familiar with the author of the web dictionary but I'm sure she or he is a lay person. The reason I used "somewhat erroneous" is , I knew in advance I would be challenged on this. The general public has no real need to distinguish between the two and as a matter of convienence can interchange the two words, however geocachers are amatuer surveyors ,like it or not, and should strive to use the language of the profession, not to be confused with jargon, and be aware of the difference. For example, the following is copied directly from the National Geodetic Surveying data sheet page and makes the distinction between the two:


Datasheets for horizontal control stations
show precise LATITUDE and LONGITUDE

Datasheets for vertical control stations (a.k.a. Bench Marks)
show precise Orthometric Heights (Elevations)

Dictionary.com actually used multiple dictionaries. The definition I quoted was from
The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2000 by Houghton Mifflin Company

I understand that lots of professions give more precise definitions to words than the general public, especially lawyers.

All I was trying to point out was in this case the general public, the dictionary and geocachers tend to use benchmark in the same way. Which has very little bearing on how a surveyors or computer professionals use the term benchmark.