>
> I would pretty much never give up an 800-foot shot just to balance FS and BS. I'd keep the 800-footer and, if vertical is a big concern, shoot it both ways with as little time lapse as is practical in order to get the same atmospheric conditions for both shots. The C+R errors will effectively cancel out.
>
> I recently had to transfer vertical across a river in 3 places. Distances ranged from 630 to 750 feet. The differences between the reciprocal mark height calculations at the 3 sites was between 0.02 and 0.03 foot.
>
> Edit: I used a Leica T2000 on one side and the Geodimeter GDM640 on the other. Both are nominally 1-second guns.
Aloha, Jim:
John H. mentioned about reciprocal observations method you described here. So you make two observation then mean out the values--correct?
Thank you for sharing!
Edit: I just found after looking through Survey Pro user manual. It has mode to do the reciprocal observation--to eliminate C&R!
> I hope you don't mind clarifying a bit more for me...
>
> If I were to do both loops together I do have to sacrifice my horizontal traverse distance in favor of the vertical. Right? We are talking about reducing from 800 feet to perhaps 300 feet. Then I do have to balance the foresight and the backsight.
No problem at all. I would basically "carry elevations" while you are performing your horizontal traverse. Again it depends on your accuracy requirements. If I were shooting vertical angles on an 800' leg, I would try and turn the angles in the morning to avoid heat waves, and I may turn several sets of vertical angles (F1 & F2). It is especially important to minimize the amount of time between sets of angles because the tripod legs tend to expand/shrink with the changing sun, which can greatly affect your vertical angles. To experience this, set your tripod up so you have to straddle a leg to look at your foresight. Align your crosshairs with the vertical sight then shade the leg and watch your crosshairs move. Some times of the day/year are worse that others and some tripod types are worse than others. Letting the legs and the instrument acclimate is also important.
When calculating trig elevations, you are only measuring the difference between 2 points - measuring from #1 to #2 is your foresight and measuring from #2 back to #1 is your backsight. The foresight and backsight are exactly the same length. When it comes to your horizontal traverse, yes it is always good to have semi balanced traverse legs, but really what you are looking for is avoiding an 80' backsight going into an 800' foresight. Really lopsided leg lengths.
Again, I would avoid automated canned routines on the total station and set it to a basic mode, where all it does is display the raw data, which can be recorded in a field book. Once that is mastered..old school..then proceed to using software programs for your traverse work. Perhaps a few old timers here would be willing to post a picture of their field book format.
Good luck.
good tip, thanks Jim. My first reaction was, no the error would be the same both ways, but of course it cancels out like a collimation error.
I had a problem with trig levels over 250m. Further than I would normally go but I was having to traverse through s quick as possible. Another engineer did a very thorough double level run and the levels errors were about 50mm from memory.
I came here for advice but neglected to mention that this was through a tunnel in winter. The walls of the tunnel were probably warmer than the outside air. The air in the tunnel was a bit warmer.
I was wondering afterwards if it was a refraction problem. I might dig out the data file and see if I could get the right levels by averaging fore and back sights.
> Perhaps a few old timers here would be willing to post a picture of their field book format.
Not exactly a field book, but here's a sample of the reciprocal river crossing field sheet/worksheet we used recently. It includes data transferred in the office from the corresponding field sheet across the river.
Jim, I like that you measured in meters and feet. Modern instruments don't toggle as easy between units as they used to. Really provides an independent check and avoids costly problems from people that like to reverse numbers.
> people that like to reverse numbers.
Kind of like me. Notice how I put the feet in the meters column, and vice versa, for the distance entries? Thus the little hand-drawing double arrow above the columns headers.
> > I hope you don't mind clarifying a bit more for me...
> >
> > If I were to do both loops together I do have to sacrifice my horizontal traverse distance in favor of the vertical. Right? We are talking about reducing from 800 feet to perhaps 300 feet. Then I do have to balance the foresight and the backsight.
>
> No problem at all. I would basically "carry elevations" while you are performing your horizontal traverse. Again it depends on your accuracy requirements. If I were shooting vertical angles on an 800' leg, I would try and turn the angles in the morning to avoid heat waves, and I may turn several sets of vertical angles (F1 & F2). It is especially important to minimize the amount of time between sets of angles because the tripod legs tend to expand/shrink with the changing sun, which can greatly affect your vertical angles. To experience this, set your tripod up so you have to straddle a leg to look at your foresight. Align your crosshairs with the vertical sight then shade the leg and watch your crosshairs move. Some times of the day/year are worse that others and some tripod types are worse than others. Letting the legs and the instrument acclimate is also important.
>
>
>
> When calculating trig elevations, you are only measuring the difference between 2 points - measuring from #1 to #2 is your foresight and measuring from #2 back to #1 is your backsight. The foresight and backsight are exactly the same length. When it comes to your horizontal traverse, yes it is always good to have semi balanced traverse legs, but really what you are looking for is avoiding an 80' backsight going into an 800' foresight. Really lopsided leg lengths.
>
> Again, I would avoid automated canned routines on the total station and set it to a basic mode, where all it does is display the raw data, which can be recorded in a field book. Once that is mastered..old school..then proceed to using software programs for your traverse work. Perhaps a few old timers here would be willing to post a picture of their field book format.
>
> Good luck.
Aloha, Imaudigger:
Thank you so much!!
Okay, now I have better understanding of the process than I ever had before. I will do a trial loop. And will post back my result and the long hand calculation method for comments. I agree...my brain works better when I know the "whys" and "hows" instead of just pushing the buttons!
> Edit: I used a Leica T2000 on one side and the Geodimeter GDM640 on the other. Both are nominally 1-second guns.
Aloha, Jim:
You edit is that not clear to me...why use two Total Stations? Wouldn't you need a prism on the BM your sighting? I am sure there is a obvious reason...
Aloha, Jim: Thank you for posting this example. I need to study it a bit. May have few questions...
First question,
In you data reduction section, I know the Z angle at OCC can be obtained from the gun. How did you get the Z angle at the Target?
Thanks!
>
>
> In you data reduction section, I know the Z angle at OCC can be obtained from the gun. How did you get the Z angle at the Target?
This wasn't for a typical traverse scenario, but for elevation transfer across a river. We had two theodolites (one a total station) set up on opposite sides of the river. When one observer finished measuring zenith angles he replaced his gun with a target, and the other observer replaced his target with a theodolite. Distances weren't critical for this project, so they were only measured from one side.
> > In you data reduction section, I know the Z angle at OCC can be obtained from the gun. How did you get the Z angle at the Target?
>
> This wasn't for a typical traverse scenario, but for elevation transfer across a river. We had two theodolites (one a total station) set up on opposite sides of the river. When one observer finished measuring zenith angles he replaced his gun with a target, and the other observer replaced his target with a theodolite. Distances weren't critical for this project, so they were only measured from one side.
Aloha, Jim: Thanks that answers to both my questions. The other one being why use two guns. You hit two mangos with one stone!
Aloha.
This is somewhat of a sidetrack, but might be interesting background for yswami. Your situation sounds like a problem that came up with pipe lasers, back in the 70s when they were new. The air would stratify in the pipe, with colder air at the bottom, and the laser line would be bent downward by refraction. The solution was to set up a blower to keep the pipe full of air of a uniform temperature.
yswami,
I don't know what's wrong with these "surveyors" on here, but the earth is flat, at least to a cadastral surveyor 🙂
For proof I offer this It's a flat world after all !
Don't let them confuse you too much!!
Dtp
I daresay you could measure the angles by sighting the other instruments telescope as well. (but not the distance).
> yswami,
>
> I don't know what's wrong with these "surveyors" on here, but the earth is flat, at least to a cadastral surveyor 🙂
>
> For proof I offer this It's a flat world after all !
>
> Don't let them confuse you too much!!
>
> Dtp
Aloha, Don:
I didn't realize people still believe the earth is flat, leave alone a society for it! I learn something new everyday!
[sarcasm]On a serious note:[/sarcasm]
Don, you should have reminded everyone about the flat earth when we had several long heated discussions couple weeks ago about combined scale factor. You missed it big time! 😀 😀 😀
> I daresay you could measure the angles by sighting the other instruments telescope as well. (but not the distance).
Aloha, Squowse:
It was actually mentioned to me by one of the poster when I asked about doing the collimation calibration. By pointing at another instruments lance--let's say about couple meters apart in a control environment--the collimation adjustment can be accomplish with better accuracy. Unfortunately, "recreational surveyor" like me only have one instrument! 😉
Thank you for chiming in!
This graph is interesting John, can you tell me the source please as I would like to read in more detail?
I am currently assessing reciprocal vertical angle measurements and calculating the refractive measure K.
I am getting wildly different values of K. I think I have got the formula right.
I am using
error = true height difference - measured height difference (generally positive, height is measured lower due to curvature)
C&R factor = error / (distance in km) ^2
Then
K = (0.078 - C&R factor) / 0.078
The K is expressed as a proportion of the earth's curvature I think? Which is 0.078 in metric?
One thing that strikes me as strange is that the accepted standard value is positive 0.18, but the graph shows it going negative through the day.
