> Aloha,
> I always noticed in my Survey Pro preferences there is a choice for surveying with "True Azimuth."
> I never used it before. But I want to understand this better.
>
> 1. Do one uses surveying with true azimuth when one have to deal with a situation where the previous survey's azimuth was assumed? Or other reasons?
>
> 2. When I setup on the known point and back sight to another known point the software shows the correct azimuth as described in the deed, so I am surveying with true azimuth right? (The azimuth in the DC is correct when compared to the actual true North in the field..)
>
> Any clarifications anyone willing share will be very much appreciated--if you can spare few minutes of your valuable time!
>
> Thank you!
This ought to get interesting. The term is a misnomer at best. You really can't ever survey with true azimuths, but only correct up into them from some observations on a celestial body (star, sun, moon, et cetera). The term is for old fogies who liked azimuths instead of angles or bearings. To be fair, using a $3 calculator with sin, cosine and tangent, I'd rather compute based off of azimuths than bearings as the sign is preserved in the calculation of the latitude and departure.
I can't wait to see the True Vs. Geodetic crew show up and hash this out.
Short answer, it's the azimuth computed between the points and not an azimuth as derived from a celestial observation.
What I described above was used more with transits than anything and we've never really done it. It's about as archaic today as surveying with deflection angles, which is a real headache unless the note keeper is on his toes. With transits, you have a right and left plate, which made for time saving techniques to be incorporated in the field for office work. With the advent of the theodolite, the instrument turned one way (angle right or left) so some of it went by the wayside, but you could still do it. Deflection angles really did.
That was my only gripe about the TopCON GTS 303 was that the meter to feet button was right by the angle right to angle left button and a careless instrument man has busted many a traverses, usually when turning near 180° which was impossible to catch without a total rerunning of the traverse.
> This ought to get interesting. The term is a misnomer at best. You really can't ever survey with true azimuths, but only correct up into them from some observations on a celestial body (star, sun, moon, et cetera).
I think you are correct in general. Do note that you could correct up the bearings based on your latitude using the old BLM "red book" (or an adequate software) and correct each angle turned and correct your foresight angle to reflect "true" azimuth. But I would suspect that the software doesn't do that for you. Also, it would make for 'apparent misclosures' that are based on running plane x/y coordinates with spherically corrected azimuths.
Still, and regardless, we always use plane geometry when we run angles and distances and use a plane X/Y coordinate base which is equally not "true".
> > This ought to get interesting. The term is a misnomer at best. You really can't ever survey with true azimuths, but only correct up into them from some observations on a celestial body (star, sun, moon, et cetera).
>
> I think you are correct in general. Do note that you could correct up the bearings based on your latitude using the old BLM "red book" (or an adequate software) and correct each angle turned and correct your foresight angle to reflect "true" azimuth. But I would suspect that the software doesn't do that for you. Also, it would make for 'apparent misclosures' that are based on running plane x/y coordinates with spherically corrected azimuths.
>
> Still, and regardless, we always use plane geometry when we run angles and distances and use a plane X/Y coordinate base which is equally not "true".
I suppose you are right to point out that it's a generalization on my part. Truly you can run True/Geodetic North fairly easy, but to run a latitudinal line, well that would require you to be on the equator and use plane surveying techniques. 🙂
> With the advent of the theodolite, the instrument turned one way (angle right or left
As I recall, you could read angle left or right on a T16. As an aside, most of the guns we commonly call "transits" are actually theodolites.
> > With the advent of the theodolite, the instrument turned one way (angle right or left
>
> As I recall, you could read angle left or right on a T16. As an aside, most of the guns we commonly call "transits" are actually theodolites.
I never ran a T16 so I can't speak intelligently to that, and it wouldn't surprise me to see a right/left theodolite, but I've never ran one. The ones we have were all to the right. It wasn't until the digital guns when I ever had to turn an angle left as I never had to actually run (for very long) the K&E paragon.
Not that I'm old or anything, but when I started running the run, we had just retired the Leitz 20" theodolite and K&E autoranger. My first gun was the old GTS2B and I thought I was in hog heaven GETTING to tote that instead of the theodolite AND distance meter. 🙂
> ... As an aside, most of the guns we commonly call "transits" are actually theodolites.
As I learned it the original machines were referred to as "Transiting Theodolites". After development in Europe they kind of shortened the name to "Theodolite" and in America they shortened the name to "Transit". I have always known the ones with the external verniers as "transits" and the ones with the internal verniers (which read to a higher precision than transits) as theodolites.
> Not that I'm old or anything, but when I started running the run, we had just retired the Leitz 20" theodolite and K&E autoranger.
I guess I've actually edged into the "old" category, so even though I still think of myself as a newcomer, most around me don't see it that way. I came in during the last gasps of open-vernier transits and taped distances -- at least in my area of California -- and marveled at the rapid sophistication of the EDM and total station. And then, of course, there's GPS.
Referring again to the T16 and similar instruments, the obsolescence of the Wild and Kern optical guns as production tools doesn't do anything to reduce their value as impressive examples of mechanical design and production. Like Curta calculators, I believe they'll always hold a place of respect in the hearts and minds of folks who appreciate high-quality machines.
