I'm dealing with a highway ROW plan from the 1950's, and the calcs aren't coming out well. The parameters from the plan are as follows:
ingoing tan: N 32 deg 4' E 749.98
outgoing tan: S 80 deg 16' 45" E 749.98 brgs are magnetic, so I'd think that they were measured.
Ang = 66 deg 24' 15" (subtracted value is 67 deg 39' 15")
LC = 1328.07, of course, used for stationing
R = 1146.28
The curve was changed at that time, so it had to be staked out on the ground.
I'm inclined to hold the brgs and LC, since they were measured, but:
1: How did they calc that stuff in 1955? I wasn't precocious enough to be doing circular curves back then. Angles are, of course, easy to subtract and that's where'd I'd have started.
2: That leads to: which value(s) did they blow, and why?
Well, it appears to be a 5å¡ Chord Definition (Railroad) curve, which might indicate that "they" were using "tables" such as in Searles & Ives. If so, then the Length of Curve (from the tables) will be different than one would get using (Delta * Radius * Pi) / 180. If in fact "they" were using a "compass" then there is a chance that the "observed" Bearings Fore & Aft out of the PI (assuming that they occupied it) were later corrected for the local variation coming IN from the "other end" of the Lines. I dunno, stuff like this can be a real PITA, but you can generally dope it out by running different scenarios.
Loyal
I'm going out to shoot centerline now, but the magnetic bearings ended up on the plan.
Do you think they used the other tables if they ran out of the other "paper" on the job and had to use them? 🙂
After shooting the centerlines (and making allowances for the nearby rock face on the outside of the curve that they may have had to adjust to), I came back and noticed that the R = 1146.28 was repeated on the next curve over.
The odds on that happening were slim to none, while the odds of a transcription error were more likely. The other curve calcs worked out well. The computed radius was 1124.73, but the actual road fit well with 1170.3. So well, it was likely laid out by an engineer/surveyor.
Of course, it could have been slightly altered in a post-1955 repair project and never mentioned.
