One for the techies...
Well, I finally got a mostly cloudy day after waiting for two weeks. So, off we went to the CBL. Now, I use the Morris CBL in New Jersey, which can be found in the nj.his file at the NGS Calibration Baseline page. The CBL is listed as unsafe, which I assume is because of nearby traffic conditions and the fact that parking along the line can be difficult. But, I know the base and use it quite often and my only problem is with vegetation.
So, here's the CBL data, for those too lazy to google it. Hopefully, this will be pretty clear - filewise. The average elevation of the CBL is 78 meters.
Of course, there are some considerations in using a CBL and centering is right up there. So, we break out my WILD NL, which is rated at 1 in 200,000 (or 0.0015 of a foot in 300 feet).
We kept the setups pretty low in the middle of the line so we would not have to remove tripods and reset them. 
As I mentioned, vegetation plays into this CBL. I have been "trimming" these bushes for years.
A view from the 150 meter monument to the 300 meter monument.
One of the CBL disks.
Being "orderly people" we occupied the 0 meter mark first. You can see the box for the WILD NL and the boxes for the two instruments being tested. A Leica TCR 802 (2mm +/- 2ppm) and a Leica TPS 1201 (1mm +/- 1.5mm).
Now that we have finished the "calendar photoshoot", here's some interesting data;
The Leica TCR 802
The Leica TPS 1201
The 1201 has just returned from the shop.
I found the results interesting...but I won't say anymore.
Oh yeah, how about a "beefcake" shot?
Here's the boss, contemplating work...
What's that??
"Beefcake" standing with 1 foot in the travelway without a vest on??:-O
What's that??
Scott, it looks like you've used 1.00 as the value of n. I'm struggling through some CBL measurements right now as a self-imposed educational task, and it's not clear to me how n figures into the process. According to NGS-10, it's the "nominal index of refraction as recommended by the manufacturer." But is it set in the gun by the user, or is it built into the EDM's displayed results without being revealed to the user?
In the one example shown in NGS-10, the value of n is given as 1.0002782, but the instrument isn't identified. My data set is from a Leica DI2002, but I can't find anything about a nominal index of refraction for Leica instruments.
Thanks for any insight you can provide.
What's that??
The "n" used here is for the least squares reduction. It is merely a count of the number of observations.
The observations were reduced before entering into the spreadsheet.
Some "useful" info can be found here;
http://www.land.vic.gov.au/CA256F310024B628/0/2AC14DC8753E005DCA257339000516E3/$File/EDM+Handbook+V9.0.pdf
Particularly for you around page 22.
You could also contact John Nolton.
He probably has the manual that would give the technical data you need.
What's that??
Here are the relevant formulas I was referring to, from NGS-10:
I'll see if I can reach John.
Thanks.
What's that??
Jim,
Obviously a question the instrument manual could resolve.
If you can alter the atmospheric data in the EDMI than the equation is irrelevent.
If the weather data is "set" by the menufacturer (WILD) then the equation is quite important.
John, has until recently had a DI2002. If I know John, he still has a copy of the manual, even if he sold the EDMI.
Nice post,
the title made me wonder what a CBL could be, your story and the pictures made it clear. I'm not aware of any public documented CBL's in Belgium.
Thanks for sharing,
chr.
There is a state law, in Washington, that says you must check your EDM, periodically, on a calibrated base line.
Is that the same everywhere?
Radar
> There is a state law, in Washington, that says you must check your EDM, periodically, on a calibrated base line.
No such requirement in CA.
Once a year in Joisey..
A link to some info on the Loenermark CBL NE of Arnhem, Netherlands. Established by the Finns, it is now abandoned in poor shape. Cool pics of a 1955 base, though.
http://www.geocaching.com/seek/cache_details.aspx?guid=8e1c598e-a015-4938-a7fe-650146968022&log=y&decrypt=
I was just out at ours earlier this year when gun returned from being serviced. Seems like a regular part of keeping your equipment in good repair regardless of whether it is a specific requirement.
I don't find MORRIS in the current NGS list, possibly because of the traffic safety issue.
Google found a history listing that includes it.
I'd throw out all data taken from the 150 meter point and re-run the analysis. It measures short on one side and long on the other, nearly the same when done from either end.
NGS hasn't remeasured it since 1980.
LIST OF ADJUSTED DISTANCES (NOVEMBER 12, 1980)
A lot of freeze-thaw action can happen in 30 years.
Bill,
You are 100% correct.
I was wondering when someone would look at the actual data.
And, I did say it wasn't a current baseline.
Ours goes back to the dealer for service each year, we get a calibration report then that we need to deliver for some of our jobs. It's also implemented in our ISO-system.
chr.
As I posted on that other board in May, I use calibrat.exe (NGS, DOS program) to compute the scale and offset after I visit the CBL each year. I loaded up the Cessna and we flew up to the Titusville (PA) baseline in May. It is situated at a small airport, adjacent to the runway.
I pre-process the data before loading into calibrat. I download the raw data and use the uncorrected values. I apply temperature and pressure corrections, then the prism offset, then reduce to mark-to-mark values using the observed vertical angles and HI/HT. You can also reduce to M-to-M using the mark elevations abd the HI/HT.
I use a prism that is nominally -30 offset, but since I don't necessarily trust that, I first ran the analysis using 0 for the prism offset:
Trimble S6 NO OFFSET
05-26-2010
MANUFACTURER'S SPECIFICATIONS: +1 MM
+1 PPM
SCALE ERROR = +0.7037 PPM
STANDARD ERROR OF SCALE = +0.4937 PPM
CONSTANT ERROR = -0.0306 METERS
STANDARD ERROR OF CONSTANT = +0.0003 METERS
VARIANCE OF UNIT WEIGHT = +0.2282
COVARIANCE = +0.1222
CORRELATION = +0.7762
PUBLISHED OBSERVED DIFFERENCE RESIDUAL
(METERS) (METERS) (METERS) (METERS)
430.0576 430.0873 -0.0297 +0.0006
1503.1362 1503.1650 -0.0288 +0.0007
280.0417 280.0720 -0.0303 +0.0001
1353.1199 1353.1507 -0.0308 -0.0012
150.0164 150.0474 -0.0310 -0.0005
430.0576 430.0875 -0.0299 +0.0004
1073.0792 1073.1091 -0.0299 -0.0001
280.0417 280.0723 -0.0306 -0.0002
Okay, so it looks like the prism offset is -30.6 mm. Of course, that includes any offset in the gun itself.
So, I re-run using -30.6:
Titusville S6 -30.6 offset
05-26-2010
MANUFACTURER'S SPECIFICATIONS: +1 MM
+1 PPM
SCALE ERROR = +0.7037 PPM
STANDARD ERROR OF SCALE = +0.4937 PPM
CONSTANT ERROR = +0.0000 METERS
STANDARD ERROR OF CONSTANT = +0.0003 METERS
VARIANCE OF UNIT WEIGHT = +0.2282
COVARIANCE = +0.1222
CORRELATION = +0.7762
PUBLISHED OBSERVED DIFFERENCE RESIDUAL
(METERS) (METERS) (METERS) (METERS)
430.0576 430.0567 +0.0009 +0.0006
1503.1362 1503.1344 +0.0018 +0.0007
280.0417 280.0414 +0.0003 +0.0001
1353.1199 1353.1201 -0.0002 -0.0012
150.0164 150.0168 -0.0004 -0.0005
430.0576 430.0569 +0.0007 +0.0004
1073.0792 1073.0785 +0.0007 -0.0001
280.0417 280.0417 +0.0000 -0.0002
It looks like it meets the specs for the gun, namely 1 mm + 1 PPM. Since we do a lot of monitoring surveys June-September, I try to get to the baseline before we start the rounds in the summer.
