USGS Benchmark accuracy...?
Hello, Timenutters--
There is a USGS survey benchmark on the side of the road
just a half-mile from my house.
Any guess as to how accurate these are?
I parked my pickup truck over the benchmark with the LH
box and antenna ( a 10 year-old Trimble surveyors antenna).
I only let LH run for an hour-- I am not sure how I could
leave a LH box out there for a long survey period without
running the risk of theft. The survey marker is about 20 feet
off the side of the road in a grassy area and marked only by a
4-foot-tall plastic USGS geodetic pole next to the buried
concrete post.
The head of the marker post with the brass plate on the top
is flush with the surface, but covered with grass. I had to
scratch around to find it. There is also a second concrete post
in the ground about 30-40 feet away-- apparently you line up
the two concrete markers to give you a true cardinal direction.
Mike Baker
Howdy Timenuts-
It has been a few years since I went to school on these, and there have been
some changes. Basically, to find out the specifics on the benchmarks, you can go
to the USGS website, and search for the benchmark, from the info on the brass
plate. You can find the 'Order' of the benchmark, which will tell you its
accuracy. In my time, there were 1st, 2nd, and 3rd order benchmarks, but they
have since re-surveyed some of the benchmarks, now designated as 'High
Accuracy'. Good luck. -
Dave Powers
From: Michael Baker mpb45@clanbaker.org
To: time-nuts@febo.com
Sent: Wed, September 14, 2011 7:39:44 AM
Subject: [time-nuts] USGS Benchmark accuracy...?
Hello, Timenutters--
There is a USGS survey benchmark on the side of the road
just a half-mile from my house.
Any guess as to how accurate these are?
I parked my pickup truck over the benchmark with the LH
box and antenna ( a 10 year-old Trimble surveyors antenna).
I only let LH run for an hour-- I am not sure how I could
leave a LH box out there for a long survey period without
running the risk of theft. The survey marker is about 20 feet
off the side of the road in a grassy area and marked only by a
4-foot-tall plastic USGS geodetic pole next to the buried
concrete post.
The head of the marker post with the brass plate on the top
is flush with the surface, but covered with grass. I had to
scratch around to find it. There is also a second concrete post
in the ground about 30-40 feet away-- apparently you line up
the two concrete markers to give you a true cardinal direction.
Mike Baker
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Hopefully it is better than the ones that denied Georgia a piece of
the Tennessee river - just about one mile off... Interesting topic in "How
the States got their shapes" on History channel.
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Michael Baker
Sent: Wednesday, September 14, 2011 5:40 AM
To: time-nuts@febo.com
Subject: [time-nuts] USGS Benchmark accuracy...?
Hello, Timenutters--
There is a USGS survey benchmark on the side of the road
just a half-mile from my house.
Any guess as to how accurate these are?
I parked my pickup truck over the benchmark with the LH
box and antenna ( a 10 year-old Trimble surveyors antenna).
I only let LH run for an hour-- I am not sure how I could
leave a LH box out there for a long survey period without
running the risk of theft. The survey marker is about 20 feet
off the side of the road in a grassy area and marked only by a
4-foot-tall plastic USGS geodetic pole next to the buried
concrete post.
The head of the marker post with the brass plate on the top
is flush with the surface, but covered with grass. I had to
scratch around to find it. There is also a second concrete post
in the ground about 30-40 feet away-- apparently you line up
the two concrete markers to give you a true cardinal direction.
Mike Baker
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
On Wed, Sep 14, 2011 at 08:39:44AM -0400, Michael Baker wrote:
Hello, Timenutters--
There is a USGS survey benchmark on the side of the road
just a half-mile from my house.
Any guess as to how accurate these are?
No guesses, but for something in the NGS, you can find
out. However, many USGS marks were placed for USGS mapping
purposes, and may not be terribly useful otherwise. If it was
a well surveyed USGS mark, it could be part of the national
system.
The head of the marker post with the brass plate on the top
is flush with the surface, but covered with grass. I had to
scratch around to find it. There is also a second concrete post
in the ground about 30-40 feet away-- apparently you line up
the two concrete markers to give you a true cardinal direction.
Unclear as to whether you've found an Azimuth mark (in
which case it's horizontal position won't be well surveyed at
all -- it's not intended as a horizontol control) or just the
witness posts associated with the primary mark.
If the others aren't witness posts (designed to help
you locate the reference), then this sounds like an azimuth
marker and its associated reference, which were only located
with enough precision for a surveyor to be able to find it later.
Different marks were intended for different things
(elevation, horizontal position, azimuth, cadastral survey,
etc.)
What were the markings on the disc? If it's part of
the NGS (and not just a USGS BM), a data sheet is available
online. Also, where is it?
Any pictures?
--msa
On Wed, Sep 14, 2011 at 9:52 AM, Jose Camara camaraq1@quantacorp.com wrote:
Hopefully it is better than the ones that denied Georgia a piece of
the Tennessee river - just about one mile off... Interesting topic in "How
the States got their shapes" on History channel.
In one sense a BM's position is dead-on perfect. The marker only
says "my name is "X" and I am at the position marked by this cross."
By definition it can't be in error.
Then you look up in some database and find the last surveyed location
of the BM. Now that might have an error or not. The location of the
marker near me is at the fraction of an inch level now but apparently
in the 1940's it was way off by several feet because everyone's
property lines are wrong and the city is making people get new surveys
if they pour any new concrete foundations.
So the accuracy of the same BM can change over time as it is
re-surveyed using better methods
Chris Albertson
Redondo Beach, California
Hi Chris:
And there's the problem that the BM is moving.
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.End2PartyGovernment.com/
Chris Albertson wrote:
On Wed, Sep 14, 2011 at 9:52 AM, Jose Camaracamaraq1@quantacorp.com wrote:
Hopefully it is better than the ones that denied Georgia a piece of
the Tennessee river - just about one mile off... Interesting topic in "How
the States got their shapes" on History channel.
In one sense a BM's position is dead-on perfect. The marker only
says "my name is "X" and I am at the position marked by this cross."
By definition it can't be in error.
Then you look up in some database and find the last surveyed location
of the BM. Now that might have an error or not. The location of the
marker near me is at the fraction of an inch level now but apparently
in the 1940's it was way off by several feet because everyone's
property lines are wrong and the city is making people get new surveys
if they pour any new concrete foundations.
So the accuracy of the same BM can change over time as it is
re-surveyed using better methods
Chris Albertson
Redondo Beach, California
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
That certainly happens, on a short time scale even, across fault lines.
Kinda makes you wonder about dams and other big structures.
-John
===============
Hi Chris:
And there's the problem that the BM is moving.
Have Fun,
Brooke Clarke