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.
?ÿ
JOHN NOLTON
I followed Bill's link, and then got curious about the availability of gyrocompasses on eBay.?ÿ I got a kick out of the caution painted on this one:
@john-hamilton Interesting story, was it a DMT Gyromat? That must be quite cumbersome. Not a easy trip.
@beuckie DMT Gyromat 3000 and Gyromat 5000 seems more accurate, with accuracy 5" and 3". When the gyros are mounted on top, it is not as stable as those with gyros put underside. Though I don't know if it has caused the accuracy difference.
Well, geezo wheezo John.?ÿ Of course I know that the Wild GAK determines astronomic north; however the PhD geodesist knew otherwise. Being a very gneiss geologist I was trying to be tactful rather than tacky in noting the learned geodesist's mistake. Once someone understands that the gyro is working in a gravity field, the answer is easy.
I was also gently attempting to point out that for normal situations where the Laplace correction is small (or as we geologists/geophysicists like to think, the slope of the geoidal surface is near zero), which makes the correction between geodetic and astronomic north de minimus (yes, it is easy to account for that systematic error in the computation).?ÿ
Oh, and sorry we rockheads use the term baseline instead of base line; sort of like our preference for groundwater rather than ground water.?ÿ We're a crusty crowd so there's not much use teaching us anything, but you old geodesists can bit a bit on the crusty side too, also! 🙂
Otherwise, I hope this note finds you hale and hearty and still enjoying the warmth of the Chihuahuan Desert. I hear that the BLM has been surveying all of the mineral surveys in your area.?ÿ If you are still in contact with Scott Z. tell him hi for me. I imagine that he is retired now and hopefully enjoying his spare time with his old survey instruments, esp. the GAK gyro.
Cheers,
Gene
Just to clarify, in case somebody doesn't think it through. The gyro is kept powered up whilst being taken from the surface to underground.
That image brings back memories. In the days before GPS was commonplace in survey (i.e. expensive!) we used to use one (hired from the local university) to calibrate the compasses on drilling rig vessels when they were in port for some purpose.
We did one on Teesside (UK) and thought no more of it. Three months later we had a message from the south atlantic, off the Falkland Islands. They had positioned over where they thought they had left off the previous season, dropped the drilling rod and it had gone straight into the seabed docking unit!
Once in a lifetime closure.
