Back2Basics: Surveying with True Azimuth

I'm not sure but I think it means the software puts the azimuth in for the backsight instead of zero. FS minus BS = angle right.

Trimble access defaults to azimuth instead of zero.

This does not mean you are using actual true (astronomic or geodetic) azimuth. The survey you have may not be exactly true if it used a record basis of azimuths.

We survey, collect data or traverse around something using angles and distances, we use Degrees, Minute and Seconds for angles and feet to express distance, but some around the world use Mills and Meters, heck could use Radians and cubits.
To define a line we must express direction in some form that divides a 360 degree circle in some manner then we show how far along that direction to to go to the end point, that defines the direction and length of a line, we show it on drawings and use it in descriptions to express intent that can be measured.

Bearing: S 45° E 1320.00 feet.

North Azimuth: 135° 1320.00 feet.

South Azimuth: 315° 1320.00 feet.

All the same line when using a common starting point.

Normally, we don't know direction to a high enough precision to use Bearings, Azimuths or whatever in the field. We do have the ability to determine a direction to that quality but normally we just measure angles, shoot distances and determine direction based on North, grid, magnetic or geodetic etc....
jud

I think you are right Dave. In Survey Pro this is the difference between collecting raw data angles as "angle right (or left I guess)" vs "azimuth"

Put another way...

A set of angles...

BS 1
F1 00-00-00
F2 180-00-10 m=00-00-05

Instr. @ 2

FS 3
F1 45-00-00
F2 225-00-20 m=45-00-10

Angle right=45-00-05

Say the azimuth from 2 to 1 is 10-00-10 so the angles would look like this:

BS 1
F1 10-00-10
F2 190-00-20 m=10-00-15

Instr. @ 2

FS 3
F1 55-00-10
F2 235-00-30 m=55-00-20

Angle right=45-00-05

Therefore the result is the same.

Dropped the later.
Normally, we don't know direction to a high enough precision to use Bearings, Azimuths or whatever in the field. We do have the ability to determine a direction to that quality but normally we just measure angles, shoot distances and later determine direction based on North, grid, magnetic or geodetic etc... for our Comps and drawings..
jud

> I'm not sure but I think it means the software puts the azimuth in for the backsight instead of zero. FS minus BS = angle right.
>
Aloha, Dave: you are correct. If I choose true azimuth the software puts the azimuth value instead of zero. ( I do need to verify what is the value next I do a setup.)
> Trimble access defaults to azimuth instead of zero.
>
> This does not mean you are using actual true (astronomic or geodetic) azimuth. The survey you have may not be exactly true if it used a record basis of azimuths.

Okay. You are correct again, I am comparing the recorded azimuth and what I have as result of using the recorded azimuth. Thanks.

Since the computer lacks magic pixies to answer questions, it uses the coordinates stored under point numbers to 'inverse' the bearing between points (coordinate pairs) in its memory. The "True Azimuth" setting merely displays (Delta E/Delta N=tan(bearing), then convert bearing to azimuth) from Instrument Point to BS, then adds the angle right turned from the BS.

"True Azimuth" is an unconventional method in the US, likely left over from a time when field surveyors carried slide rules instead of calculators and used methods designed to reduce error-prone field computations.

A lot of the old timers were really slick about a lot of things. There was a lot of lore to learn in the 15 years it usually took to make one's way up the hierarchy from tail chainman to party chief back in the transit days.
Of course, there were a lot of them who didn't know how to do much but turn 90s, who would box around obstacles because they couldn't solve a triangle to save their lives... :woot:

> We survey, collect data or traverse around something using angles and distances, we use Degrees, Minute and Seconds for angles and feet to express distance, but some around the world use Mills and Meters, heck could use Radians and cubits.
> To define a line we must express direction in some form that divides a 360 degree circle in some manner then we show how far along that direction to to go to the end point, that defines the direction and length of a line, we show it on drawings and use it in descriptions to express intent that can be measured.
>
> Bearing: S 45° E 1320.00 feet.
>
> North Azimuth: 135° 1320.00 feet.
>
> South Azimuth: 315° 1320.00 feet.
>
> All the same line when using a common starting point.
>
> Normally, we don't know direction to a high enough precision to use Bearings, Azimuths or whatever in the field. We do have the ability to determine a direction to that quality but normally we just measure angles, shoot distances and determine direction based on North, grid, magnetic or geodetic etc....
> jud

Aloha, Jud: Thank you for the detailed explanation. This is very helpful. :good:

Back before data collectors and computers, when everything was done with a theodolite, we would survey everything with true azimuths on construction sites. Set up on a known point, N & E, backsight a known point with the azimuth in the instrument. The azimuth was calculated from the coordinates of the two points with a calculator. Turn to the azimuth of a point you want to stake, again calculated from the coordinates. Measure the distance and set the point.

There wasn't much purpose for running azimuths for land surveying but we used it in construction all the time. Data collectors eliminated any advantage of running azimuths since the DC does all the math.

James

> Since the computer lacks magic pixies to answer questions, it uses the coordinates stored under point numbers to 'inverse' the bearing between points (coordinate pairs) in its memory. The "True Azimuth" setting merely displays (Delta E/Delta N=tan(bearing), then convert bearing to azimuth) from Instrument Point to BS, then adds the angle right turned from the BS.
>
> "True Azimuth" is an unconventional method in the US, likely left over from a time when field surveyors carried slide rules instead of calculators and used methods designed to reduce error-prone field computations.
>
> A lot of the old timers were really slick about a lot of things. There was a lot of lore to learn in the 15 years it usually took to make one's way up the hierarchy from tail chainman to party chief back in the transit days.
> Of course, there were a lot of them who didn't know how to do much but turn 90s, who would box around obstacles because they couldn't solve a triangle to save their lives... :woot:

Aloha, Seymore:

Thank you for the explanations and sharing the history behind the usage...that helps to put things in perspective.

I noticed, one of my challenge is, I have no knowledge how survey was done with older instrument. Hence historical accounts helps a lot to understand how things are done in the past. For an example--if I understand it correctly--set circle in total station reflects to aligning verniers to zero. If someone never seen one in use, it is hard to visualize what the modern instrument is doing. Just pushing the button does not feel right...

15 years, Wow! that's a pretty long time.

Thanks

> Back before data collectors and computers, when everything was done with a theodolite, we would survey everything with true azimuths on construction sites. Set up on a known point, N & E, backsight a known point with the azimuth in the instrument. The azimuth was calculated from the coordinates of the two points with a calculator. Turn to the azimuth of a point you want to stake, again calculated from the coordinates. Measure the distance and set the point.
>
> There wasn't much purpose for running azimuths for land surveying but we used it in construction all the time. Data collectors eliminated any advantage of running azimuths since the DC does all the math.
>
> James

Aloha, James: Thank you!
That must be a great accomplishment--to do all those calculations in the field. Reading what a surveyors had to do those day makes me to admire the profession even more!

A common method of transit traverse I have seen is deflection angles, bottom of page to top. They also noted the bearing on the compass for blunder detection.

BS on zero, plunge the telescope, right or left to the FS and often accumulated on the plate 4 times. This made it simple to calculate the bearing of the next traverse leg.

Setting verniers or micrometers involved something called a "Lower motion", rarely seen these days, which allowed the instrument to rotate without measuring or disturbing the angle set via the "Upper motion", unclamped vernier, or "Mike" (micrometer knobs)....

It might help if you refer to "Just pushing the button" as "Zeroing the instrument", and "the backsight" as "The zero line". I've found that seems to make things more evident for the new breed of new guys.

One thing hasn't changed: no one falls out of his mother knowing this stuff. We all had to start somewhere. And it's only our personal initiative that keeps us moving forward.

> It might help if you refer to "Just pushing the button" as "Zeroing the instrument", and "the backsight" as "The zero line". I've found that seems to make things more evident for the new breed of new guys.

Very good point!
>
> One thing hasn't changed: no one falls out of his mother knowing this stuff. We all had to start somewhere. And it's only our personal initiative that keeps us moving forward.

And this is very true! :good:

> A common method of transit traverse I have seen is deflection angles, bottom of page to top. They also noted the bearing on the compass for blunder detection.
>
> BS on zero, plunge the telescope, right or left to the FS and often accumulated on the plate 4 times. This made it simple to calculate the bearing of the next traverse leg.

Although I used to "carry coordinates" all the time, I never traversed like that, but used to do it constantly 'moving up' on road & RR curves.
"BS indirect with the PC deflection for the station mounted. Plunge, and continue with standard PC deflections (L or R) until you get to the PT." - was one of the first really good bits of surveying lore I learned.

I had a crew chief who was sort of an aspie, and stuttered, and really only surveyed as a sideline to his true calling as a mathematical genius. He ran at least 5 miles every morning, ate the exact same thing for lunch every day for at least 3 years, and if he drank any water, you could count on him peeing within 5 minutes. He could stand flat-footed and derive the math he needed for anything. I had a friend who had a Master's in Math who would be gobsmacked that this stuttering scarecrow-looking guy with a correspondence school Associate's in surveying could breeze through discrete analysis problems that stumped his Doctoral advisors.
I was lucky to have worked with that guy. He taught me volumes and loved to explain the "whys" of things. He later recruited me to work for a madman engineer who could take a casual conversational 4-minute walk through a RR yard or refinery and pretty much draw a plan view of it to scale, freehand, a week later. :-O
It was pretty easy to be humble around those two. I was just happy to be there...:-$

A few years ago, I was doing a survey over Thanksgiving weekend. Since I work at the surveying toy store, I was using equipment from our stock of used total stations and data collectors.

I ran a traverse with a dozen or more setups around an odd-shaped 33 acre tract. I was working angle-right from a horizontal angle set to 0° on the backsight.

When I got through with the survey and started to process my raw data, I noticed that all the angles recorded in the raw file were there as azimuths instead of angles to the right from the backsight. At first, I was quite alarmed thinking I was either going to have to run the whole thing over again because at first glance, I thought I had some setting wrong and the data collector was reading my angles to the right as azimuths and the traverse was bollixed up beyond redemption.

But when I looked more closely, everything appeared to be in the right place, which could not at all have been the result if the data collector had been reading angles-to-the-right as azimuths.

What it did was convert all those angles-to-the-right to azimuths and record them as such in the raw data file. I cannot conceive of a reason you would ever want to do this but someone must have one because it is a setting in Survey Pro.

But as a general rule, I do not believe this is a wise practice to employ. I did not even know the option existed in what was then TDS software. When I have occasion to run a traverse now, that is one of the things I check in the data collector to be certain that box is unchecked.

You could easily work in azimuths only. You could assume your beginning azimuth if you didn't actually use a compass or do a stellar observation, and run your closed traverse back to the beginning line. The final azimuth should be close to the beginning azimuth. The difference in azimuths could/would be the angular closure. For adjustments, you would have to think about which way you need to adjust each azimuth. It would take getting used to the new mindset, but it is essentially the same process. It is primarily the issue of turning angles from zero has been the historically easiest way for us to use a theodolite. Much easier than trying to set the 180º opposite last foresight azimuth. Today, with electronic readout, you could simply run the azimuths if you wanted. It is just easier for us to think in angles and angular closure.

> A few years ago, I was doing a survey over Thanksgiving weekend. Since I work at the surveying toy store, I was using equipment from our stock of used total stations and data collectors.
>
> I ran a traverse with a dozen or more setups around an odd-shaped 33 acre tract. I was working angle-right from a horizontal angle set to 0° on the backsight.
>
> When I got through with the survey and started to process my raw data, I noticed that all the angles recorded in the raw file were there as azimuths instead of angles to the right from the backsight. At first, I was quite alarmed thinking I was either going to have to run the whole thing over again because at first glance, I thought I had some setting wrong and the data collector was reading my angles to the right as azimuths and the traverse was bollixed up beyond redemption.
>
> But when I looked more closely, everything appeared to be in the right place, which could not at all have been the result if the data collector had been reading angles-to-the-right as azimuths.
>
> What it did was convert all those angles-to-the-right to azimuths and record them as such in the raw data file. I cannot conceive of a reason you would ever want to do this but someone must have one because it is a setting in Survey Pro.
>
> But as a general rule, I do not believe this is a wise practice to employ. I did not even know the option existed in what was then TDS software. When I have occasion to run a traverse now, that is one of the things I check in the data collector to be certain that box is unchecked.

Aloha, Jerry:
Thank you! I'll never have that box checked!

I never looked at the raw data in the data collector until today. It appears to be a log of every action that was made during the job. Do surveyors use this to transfer data to other software or use it for legal purposes? i.e. proof of their work and procedures...

My need is very simple...I just export the data as .csv file and import it into Excel. Then to my cad software Vectorworks. All is accomplished on a Mac of course.

Thanks

> You could easily work in azimuths only. You could assume your beginning azimuth if you didn't actually use a compass or do a stellar observation, and run your closed traverse back to the beginning line. The final azimuth should be close to the beginning azimuth. The difference in azimuths could/would be the angular closure. For adjustments, you would have to think about which way you need to adjust each azimuth. It would take getting used to the new mindset, but it is essentially the same process. It is primarily the issue of turning angles from zero has been the historically easiest way for us to use a theodolite. Much easier than trying to set the 180º opposite last foresight azimuth. Today, with electronic readout, you could simply run the azimuths if you wanted. It is just easier for us to think in angles and angular closure.

Aloha, Tom:
Thank you. It is coming clearer now. In fact, I can see why a surveyor wants to see the raw data--that's where he gets all the angles for his measurement. I can see that t is much easier to deal with angles then azimuth when you working on your closure.