Good morning everyone,
?ÿDoes anyone know what this instrument is? It is commonly used in tunnel surveying and mining.
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Looks like a total station with a gyroscope below.
Is that one of the project you are working on? Tunnel and mine surveying are areas of the surveying profession I have never been exposed to but look very interesting. ?????ÿ
Yes a Leica T## ( the carry handle is removed) and a gyro - the gyro is setup on the surface and oriented - then taken down into the shaft where the same line is the reference - many shafts are accessed through a vertical shaft, so there is no way to back sight a line
Worked at a place that had on in 1982-83, different model, mounted on top of standards of a T2 like an old top mount EDM. Never used it, IIRC, accurate to 20"?
SHG
Yes, similar to DMT Gyromat 3000, it is a gyroscope with a Leica total station integrated.
@flga-2-2?ÿ ?ÿYes, tunnel surveying is the type of project my workmates often work on. I can share more photos if you like it.
@ross-kinnie You are so professional, Ross. Thank you for the explanation!
The instrument you recall is a Wild GAK north-seeking gyroscope. They were usually mounted onto a T-16 or a T-2.?ÿ Accuracy varies from 20" to 30" depending on the instrument used and the latitude. Wild states that the operational range is up (and down) to 75?ø latitude.
I have two working units with a third for parts.?ÿ The T-16 has an endless tangent screw that makes observing the oscillations easier than the T-2. There are two observation types. One uses an accurate clock and the other observes the reversals of the oscillations....think about observing Polaris multiple times at eastern and western elongation and splitting the difference. The instruments are very sensitive so proper procedure is to observe on a known baseline before and after the underground survey work to make sure that the "instrument constant" is the same.?ÿ By "instrument constant" I mean observing the difference in the orientation of the gyro axis and the theodlite's telescope axis.
I've had some interest in the units the last couple of years, but my leeriness to ship them has kept me from doing so. I guess I'd reconsider if somebody showed up on my doorstep waving cash.?ÿ
The one that is shown in the OP is accurate to a handful of seconds (2" to 3" IIRC), but the price is astronomic for that order of magnitude improvement in accuracy. I heard a couple of years ago there was a long wait to get one shipped from the German manufacturer.
@gene-kooper @Shelby You must mean something like WILD GAK1 or GAK11 gyro as follows. Yes, GAK11 is an old style gyro which is mounted on top of a WILD T16, or T2, etc. Modern gyros are much more accurate, but the prices are much higher.?ÿ
From what i've heard the best instrument for this is the Sokkia Gyro X II
When I bought mine, he offered to ship it (from the Netherlands), but I decided to go pick it up in person. The airfare was pretty cheap, about the same as shipping ($400). Plus, I got to spend a few days in Amsterdam...but that is another story...
He had a few others of the same design, they were all military surplus units. It was tough getting through security at the airport, I was pulled out and taken to a private room for search and questioning. And that was before 9/11. The battery and power supply were what concerned them...x-rays couldn't see inside.?ÿ
I can share more photos if you like it.
Yes, please.
The unit I have is a single piece, not separate.?ÿ
"But the price is astronomic."
ha ha
I'm glad someone enjoyed my oddball humor.
I recall a discussion with a geodesist many years ago regarding whether the Wild GAK gyros produce astronomic or geodetic north. The geodesist argued it was geodetic north. Since they require calibration on a baseline with a known azimuth in order to compute the instrument constant, one can account for either. Besides, with an instrument sensitivity of +/- 20 to 30 arc-seconds) it really doesn't matter unless you are working in an area like the Front Range of Colorado where the Laplace correction can approach 1 arc-minute.
I would imagine that for the gyro in the OP, the calibration procedures are far more sophisticated, but I'll leave that discussion to Jimmy Chou. Here is an article about the Gyromat 5000 that has a photo of a surveyor conducting calibration measurements.
If anyone wants to read more on the theory of gyroscopes, including north-seeking ones, this appears to be a good source
@gene-kooper?ÿ Gene I won't ask the name of the geodesist you talked with "BUT" a gyro (as in gyrotheodolite) determines astronomic azimuth NOT geodetic.
If the difference between astronomic and geodetic azimuth is less than +/- 20 seconds of arc then one might think that a Wild GAK gyro is determining geodetic azimuth(see your 1st 2 lines above) but in?ÿreality its an astronomic azimuth.
If you need references just let me know. Also remember its base line or base-line but?ÿNOT baseline.
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JOHN NOLTON