Unfortunately, my Dietzgen transit is not fitted with a 3-1/2" x 8 threaded base. It is somewhat smaller (perhaps a 3"?) But I still had Dad look over my shoulder as we read the vernier scale outside. Transits are incredibly simple. Vernier scales are really amazing - but I can imagine under the adverse outdoor conditions surveyors find themselves that it would be easy to misread.
On the other hand, I set up my new Kern DKM1, and even through the dim scale (it needs some TLC) I could read it incredibly fast and accurately. No doubt the Theodolite represented a huge improvement for surveyors, even if they did perform basically the same function as transits. Plus the vertical and horizontal circles could be read in one place instead of two AND you were also reading both sides of the circle in one place instead of two. Amazing technology.
I have a question regarding stadia. Was it common to use stadia when chaining for blunder checking? I recall Dad telling me about a time, as a young party chief, he was sent to redo a busted traverse. The surveyor was convinced that the problem was angular (he didn't trust the 1' transit that was used - and wanted it to be done again with his new 1" DKM2). Dad and his rod man turned each station and found every angle turned from that old transit was within 15" of the angle turned by the theodolite. (Dad attributes it to young eyes and a really good gun). So that left distances. Ultimately they found that a chained distance was transposed along one of the lines causing a 9 foot error (67 instead of 76 or something). It seems like this could happen fairly easily. But with these old instruments equipped with stadia wires, it seems like it could have been identified fairly easily. For those of you who chained, was it standard practice to check distances by stadia?
The Crandall Rule for adjusting traverses was developed by Prof. Clifford Crandall of Princeton University specifically for Transit/Stadia surveys. That's why the longer the distance, the more the error is adjusted in that/those courses.
We have it good now. TDS Ranger-I rough aim the backsight and push "take reading", the instrument automatically does a D&R then I rough aim the foresight and push "take reading" and it automatically does a D&R and continues until it has 4 sets.
Some places are hard to stand (steep and slippery).
Imagine doing that manually with a transit but not disturbing it. Backsight, flop, scramble around to the other side, turn the deflection angle, read the vernier while trying not to slide down the hill, scramble around to read the vertical angle, release the lower motion, scramble around, flop and sight the BS, etc. Our old field notes generally indicate they doubled on a 30" transit.
I have used my Dietzgen transit just for practice but that's on my level front lawn with no pressure to get the job done.
I don't remember ever checking distances with stadia after chaining it. I can see it would be a good idea.
We did have checks often. Sometimes 'double-chaining' where one guy whould hold the "foot" end and the other the decimal-foot end, then they would switch ends. Also, with tree guys, the crew chief might look down at the same foot, for a double-check. I got used to using a hand-level to make sure we were chaining level, later working with outher surveyors, I found that was not extremely common practice. Most said they could "just tell". Unfortunately, their "eye" and my hand level did not always agree. Often times the lead chainman might pace as he moved forward. That might have been a check. We always ran the traverse calculations in the field if we could to make sure we had closure.
I can remember doing a topography using stadia hairs reading an angle and distance to a rod. When it's steep enough, you had to run an extra calculation to figure out the slope-distance you 'would have' read had the stadia interval been perpendicular to the gun scope (instead of plumb).
Sorry....reminiscing a little bit.
It is possible they took more care to select transit stations.
Their traverse (40 years ago) on one line I'm working on meadered a lot more than ours. We are staying as close to the line as possible since it is so thick due to harvest within the last 20 years. This creates instrument stations that would be very difficult to turn manually.
reminisce away. that's kind of what I was looking for, although I appreciate Dave's and Cliff's thoughts as well. From what I have read that extra calculation was using cos^2 to determine the horizontal distance instead of cos. There were actually slide rules with this scale for just the purpose if I understand correctly.
> For those of you who chained, was it standard practice to check distances by stadia?
I came into the game at the end of the chaining era, so I did relatively little chaining of lines longer than 500' or so, and probably never went more than 1/2 mile at a time. However, taking stadia readings would require that the chaining crew carry a stadia rod along with them, which would slow down the operation. I never saw or heard of it being done.
I agree - carrying the rod to read stadia would have been extra load to carry. I have done a lot of chaining in my earlier days and never saw anyone using stadia to catch chaining blunders.
Transit has two horizontal plates that allow for accumulation of angles, theodolites has one, directional, and started out also using a veneer. They have been around a very long time, long before the manufacture of internal reading instruments was even possible.
jud
You can accumulate angles on many internal reading theodolite models. I don't think you can do it on a T-2 but you certainly can on a T-1 or T-16.
I realize U.S. jargon is a Transit is an open vernier type instrument and a Theodolite is an internal reading instrument but in reality they are both Theodolites and if the telescope can be flopped or transited then they are both transits.
A theodolite is any instrument designed to measure angles.
I'd never heard of it either, but I'm sure I'm not the first to have thought about it. My next question was going to be if there had ever been a range pole that was graduated to use stadia for such a purpose - then you aren't carrying anything extra...
the distinction always seemed kind of nebulous to me - except for the external vs. internal reading. But I realize that's more by use of the term than a technical one.
I don't know all of the theodolites that had two moving plates, but I started out using wild. Wild T-1's had two plates and allowed for accumulation of angles, T-2's had a fixed plate and you had to do "directional" angles. I haven't seen a theodolite with an external vernier, I thought they always had internal ones. (or maybe I misunderstood)
Dad has an old Topcon TL6DE theodolite. It accumulated angles with a lower and upper motion as well. My Kern DKM1, however is an odd duck. You can turn the circle, so as to zero up on a backsight or set an azimuth, but it does not have a lower and upper motion, just the upper.
Nor I, but did do a bunch of stockpile volumes and topography using stadia. When doing river cross sections for the USACE, data used for first flood mapping, we used a stadia board as a rod, estimating to hundredths got some surprisingly good loop closures. Used the stadia board because we were checking chained distances, as well as a differential leveling rod, Could read it clearly for longer distances.
jud
That is similar to the T2. Maybe since they have a 1" least count it was considered not necessary to accumulate angles on the plate.
The T2 has a knob for setting an angle on the plate but it isn't very fine motion.
> I have a question regarding stadia. Was it common to use stadia when chaining for blunder checking?
Nope, a rod was too much to carry.
We did read and call out the forward foot and back foot at times... and cut foot checks too
Used Stadia for lots of topo, you just had to make the slope correction twice to correct the distance... we did lots of hand calcs, and they were usually reviewed and checked a second time in the office.
Used a Beaman arc on an Alidade for a while, never used a self reducing instrument.
jud
My Dad told me the company he worked for had an instrument which automatically reduced stadia slope distances to horizontal.
Jud's comment is only the second time I've heard of it.
So there really was such a thing? Dad liked to pull people's legs, if you know what I mean.
> So there really was such a thing?
Yep. The Wild RDS is an example, though I've never seen one in the wild (so to speak).