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On Sat, 07 Feb 2009 03:36:09 -0700, Nicol�s de Hilster  
 wrote:

> . . . so to speed things up I usually use the following
> sequence (or something like it):
> ref-sun-ref-sun, transit, sun-ref-sun, turn horizontal circle,
> sun-ref-sun, transit, sun-ref-sun-ref.

OK.  The nice thing about computers (or the better calculators) taking the  
log tables out of calculations, is that the azimuth can easily be  
determined for *each* sun/time reading, and the individual results  
plotted.  Also, I now use a split time stop watch for each sun shot,  
instead of counting until the watch hits an even five second mark before  
recording.

The old way I used was to plot the Hz (or V readings before accurate  
watches became common) against the time, draw two best fit parallel lines,  
and pick an arbitrary spot on third, equidistant line for simple  
calculations.

> I teach practical hydrography and land surveying at the hydrography
> course here in the Netherlands (Terschelling) and even my students have
> no trouble to get fairly good results. The accuracy of a multiple sun
> shot as described above is around 0.005gon and up to now the average
> error has been even less than that (we always compare the sun to a very
> well known 566m long baseline).

> I have a graph on my web site showing the results of the second method
> (using that same 566m reference on Terschelling), scroll down to figures
> 9 and 10 on:  
> http://www.dehilster.info/instrumenten/theodolite2/index.html

Nice graphs.  The way I remember them (can't look now, as I'm downloading  
a large file), you made decent time with the set of eight observations,  
with good results.  Raw figures were two up, two down, two up, two down, I  
think.  Is that off center bias on the Roelofs Prism constant, or does it  
seem to depend on the observer?   Does it move with the housing, or with  
the rotation of the prism tube?

Mostly, I now wonder how much is induced when twiddling with the alignment  
of the cross hairs to the light green "clover leaves" in the prism.  I  
generally don't touch the prism through my usual six shots on the sun  
between the bracketing shots on the reference object.  Then, of course,  
the prism has to be flipped out of the way.  I think I should set up a  
high intensity strobe light at the same level as my RO, but out of the  
field of view, and see how consistently I can point between them.   I has  
assumed the difference of calculated Az in my readings between face left  
and face right was due to errors in my theodolite's preparation, but now I  
don't know.  Something else to do when the temperature becomes more  
moderate.

I saw the SunAz Java application run Monday night at the computer club.  I  
hope I now have the tools to try it at home.  We'll see.

Thanks for the program,


Richard

-- 
Richard . . .

Using Opera 9.2.4 after the "Dog" died

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