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On Thu, 05 Feb 2009 08:53:13 -0700, Nicol�s de Hilster  
 wrote:

>  I still use one of the T2's for sun shots when
> I need a reference azimuth in the field (for gyro calibrations).

That's one that I have never done.  Unless you count checking deviation of  
a compass rose for our aircraft, and I think I used another magnetic  
device for that anyway.  Are you talking about the Wild gyro for  
underground work?

How many observations do you need for your desired accuracy of xx  
seconds?  How many sun/time shots do you take each observation?  (Target,  
sun, invert, sun, target being the minimum for one observation.)

At least you don't need a neutral density filter for the objective to  
avoid burning out the electronics with the T2.  I bought a Wild Roelofs'  
Solar Prism for determining the Azimuths, works a little easier and  
quicker than the "sun's image on the notebook" methods.  No need for it,  
just a fun thing; and I can use it on the T1A (which has automatic  
compensating for the vertical circle readings) too.  The T1A is good  
enough to determine the alignment of the archaeological grids, and I  
usually use three timings on the sun face left, and three face right  
before going back to the reference object.  The little program in my HP  
solves it all on the spot, if I enter the correct data and set the  
semi-diameter to zero.  I can't find the 2009 Sokkia Ephemeris in the new  
supply catalog, so I'll have to print off Solar data from a web source  
now, I'm afraid.

Thank you very much for the screen image of Google Earth.  I failed in my  
last three attempts to find a driver that works, and was planning to visit  
our public Library to see where the   
lead, so you saved me a lot of time.

I'm glad you annotated the view, as the towers would have been hard to  
pick out unassisted, and I'm not very sure I'm reading the photograph  
correctly.  As it is, the steam clouds are hiding some, I'm sure.  The  
"470m" dimension shows the space between between which two numbers of  
towers?   Rough measurement between the towers on the East of the  
peninsula range between 180m and 660m, while on the North there is one  
stretching 1130m, unless one or two more are hidden by white clouds.   
Possibly, some of these towers were not in existence when you were there.   
I can't see where the towers go back to land, either.

Take care,

-- 
Richard . . .

Using Opera 9.2.4 after the "Dog" died

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