Measured Angle for Field Notes

Look at your closing bs. It's accounting for that not being 180-00-00 too.

Scott Zelenak, post: 439058, member: 327 wrote: Look at your closing bs. It's accounting for that not being 180-00-00 too.

Thanks for replying! I'm trying to figure out how the DC is doing the math.

You are looking at it wrong.

The measurements are BSD/FSD/FSR/BSR.
Backsight Direct
Foresight Direct
Foresight Reversed
Backsight Resvered

Some used the term indirect rather than reversed.

Subtract the the Direct Angles
Subtract the Reversed Angles
Then average the two for computed interior angle.

Field Dog, post: 439057, member: 9186 wrote:
BS 000-00-00
FS 218-14-19
FS 38-14-17
BS 179-59-57
DC corner angle says 218-14-20

218-14-19 minus 00-00-00 = 218-14-19
398-14-17 minus 179-59-57 = 218-14-20
218-14-19 + 218-14-20 / 2 =
corner angle is 218-14-19.5

Field Dog, post: 439057, member: 9186 wrote:
BS 000-00-00
FS 142-27-11
FS 322-27-15
BS 179-59-58
DC corner angle says 142-27-14

142-27-11 minus 00-00-00 = 142-27-11
322-27-15 minus 179-59-58 = 142-27-17
142-27-11 + 142-27-17 /2 =
corner angle is 142-27-14

Field Dog, post: 439057, member: 9186 wrote:
BS 000-00-00
FS 210-03-20
FS 30-03-20
BS 180-00-03
DC corner angle says 210-03-18

210-03-20 minus 00-00-00 = 210-03-20
390-03-20 minus 180-00-03 = 210-03-17
210-03-20 + 210-03-17 /2=
corner angle is 210-03-18.5

Field Dog, post: 439057, member: 9186 wrote: I'm trying to figure out what my actual measured angle is for my field notes. I will give three examples.
BS 000-00-00
FS 218-14-19
FS 38-14-17
BS 179-59-57
DC corner angle says 218-14-20
BS 000-00-00
FS 142-27-11
FS 322-27-15
BS 179-59-58
DC corner angle says 142-27-14
BS 000-00-00
FS 210-03-20
FS 30-03-20
BS 180-00-03
DC corner angle says 210-03-18
In the first example, 19" > 17". DC added 2.5" to
17".
In the second example, 11" < 15". DC added 3" to 11".
In the third example, 0" = 0". DC subtracted 1.5" from 20".
Looks like the DC is adding the mean to the smaller of the FS angles. Why? What about the third example? Why subtract the mean?

second angle: 142?§27'11" - 0?§00'00 = 142.27'11"
reverse: 322?§27'15" - 179?§59'58" = 142?§27'17"
mean = (142?§27'11" + 142?§27'17")/2 = 142?§27'14"

same with the first and third...FSreverse on the first angle passes 360 so it is 360 + 38?§14'17" The DC is meaning the two angles and the two angles are FS - BS

edit: and that is how we would have done it in the day of theodolites and paper field notes.

To explain what Lee said, in your second set, the first angle you measured was 142-27-11.

The second angle you measured was 217-32-43 {(179-59-58+360) minus 322-27-15]

Adding the two measured angles (142-27-11 + 217-32-43 = 359-57-56) results in a mis-closure of 6 seconds.

Your DC simply added half the mis-closure to each measured angle.
Ist angle 142-27-11 + 0-00-03 = 142-27-14 (exactly what your DC is showing you)

If your angle closure is over 360, it will subtract half the mis-closure from each measured angle.

I guess I'm a slow typist... the other guys beat me to it.

I agree with your Data Collector.

Field Dog, post: 439061, member: 9186 wrote: Thanks for replying! I'm trying to figure out how the DC is doing the math.

Data Collectors, may mean the angle to 1/2 second but report it differently. There are three typical defaults:
1/ always round up
2/ always round down
3/ always round to the even second (engineer's method)

1 and 2 always cause a bias in a long traverse. Method 3 tends to even things out in the long run.

I would say you have to do at least a dozen sets before what it does becomes clear. Just observe 4 different sets on each of your 3 angles. You can also set up at B, do ABC, CBA, ABD, DBA, CBD, ABC, CAB etc.

Paul in PA, PE, PLS

It looks like it is rounding odd.5 up and even.5 down.

I checked in my head and agreed with the other posters math above.

Back when I used a T-2, we would put in a small angle 10 or 20 seconds over 0 (ie 0-00-18) . and when we came back with the reverse backsight, we would have 180-00-## making it easier to subtract. However, that made it easy for a good instrument man to know what the correct return would be to make it flat.

Thank you all for replying!

I think that the problem is easier to understand if you book the angle in the traditional form:

[PRE] F Lt F Rt Mean Reduced
BS 000-00-00 179-59-57 58.5 000-00-00.0
FS 218-14-19 038-14-17 18.0 218-14-19.5
[/PRE]

DC corner angle says 218-14-20 CZECH

[PRE] F Lt F Rt Mean Reduced
BS 000-00-00 179-59-58 59.0 000-00-00.0
FS 142-27-11 322-27-15 13.0 218-14-14.0
[/PRE]

DC corner angle says 142-27-14 CZECH

[PRE] F Lt F Rt Mean Reduced
BS 000-00-00 180-00-03 01.5 000-00-00.0
FS 210-03-20 030-03-20 20.0 218-14-18.5[/PRE]

DC corner angle says 210-03-18 CZECH

"However, that made it easy for a good instrument man to know what the correct return would be to make it flat."

A good instrument man would never lie about the reading, however tempting.

2xcntr, post: 439101, member: 584 wrote: "However, that made it easy for a good instrument man to know what the correct return would be to make it flat."

A good instrument man would never lie about the reading, however tempting.

With T2/T3 I quit setting anything specific on BS a long time ago. First BS reading is whatever random angle happens to be there. Subsequent sets I advance the plate by approx amounts. If I have to subtract 25", or average 58" and 02" might as well be 315-22-25, or 315-26-58. Especially with HMS +/- calculator.

I have made a 20' mistake - for all 6 sets.

2xcntr, post: 439101, member: 584 wrote: "However, that made it easy for a good instrument man to know what the correct return would be to make it flat."

A good instrument man would never lie about the reading, however tempting.

Yes...my use of the term "good" was "bad". Lying to make one angle look good can pollute the whole network. It's kind of akin to an earlier discussion about survey plats that match the record to a "T". Makes you want to not believe any of it.

I guess I'm an old timer here. I cut my teeth as an IM on an old K & E 30" transit that didn't even have an optical plummet. Three sets direct, three reversed, N minus 2 times 180 (if I remember correctly) gave you the error of closure. By the time that data collection became common I was already in the office but routinely print out the raw data and review it when needed. Heck, I'm still using the HP 11C calculator I bought in the 80's. LOL!

What I see in our old transit notes are not sets, they are 4 deflection angles accumulated on the plate D&R alternatively. The notes look nothing like McMillan's specimen. Old timers took notes bottom up. It's easier to calc bearings from deflection angles than angles right.