I've been working thru this curve - but can't check it. I have 4 other rr maps showing the same rr Dc, delta, PC and PT but it doesn't appear to work to me. Idears???
Rankin:
Appears to be some bad data. Calc'd curve length doesn't check P.T. Station by 8 footies. 40+72.2 map = 40+80.2 calc'd from Central Angle and degree of curve using Delta*100/3. This is the same answer I get with my cogo program curve solutions.
I get a difference in arc length of 0.14 foot if I use the arc definition of the curve. Using the chord definition gives an 8' +/- difference.
Dont forget, most are spiral curves
delta 37 09 works out within reason
Check The Tangent Bearings
Using a RR curve and the curve length I get a Delta of 36°53' not 37°07'.
Using the old curve tables someone may have +/- the 7' (minutes) not -/+ it.
Paul in PA
I think you're going the wrong way with that solution :-/
Assuming the length of curve (actually being the sum of the lengths of the chords) is 1,229' per the stationing, the Dc would calc to 3d01'12"...really not that bad.
Also Check The Short Chords
There is a short chord at each end, when calculating the curve length.
Paul in PA
At the risk of stating the obvious, you have a bit of a problem.
IF this railroad was built after 1875, AND IF it crossed Public Domain Lands, THEN I would suggest getting the GLO Right-of-Way Filing Maps from the BLM (if you haven't already).
The ICC Valuation Maps can also be useful (if you don't already have them).
Inasmuch as Railroads are an Engineering proposition FIRST, and a land acquisition proposition second, I would try and get my hands on the ORIGINAL (and revised if appropriate) Engineering Drawings of the Railroad in question (often not an easy feat).
IF (as it appears) there is a typographic or even computational error on the documents that you do have, then there's a pretty good chance that you can isolate it IF you can find the right document(s).
You can often figure these kinds of things out by looking several curves each way (up and down the line), looking for another anomalous data set. Then you can work back to your curve of interest.
Some of these problems can ONLY be resolved on the ground, after LOTS of survey work. In the final analysis, that's where the rubber meets the road anyway.
Loyal
Some good advice from Loyal.
One of the things to really consider is that most of these old railroad ROWs have senior rights, and can trump anything else you try to do. And the last thing you want is to enter into one of these (potentially) nasty lawsuits, if you can avoid it in any way possible.
Ditto what Loyal said, just as a matter of due diligence.
I don't get much opportunity to deal with railroad curves, so my comments are strictly academic. But as I nosed around a bit, I found some documents suggesting that RR stationing is/was generally figured on chord lengths rather than arc lengths. I know what follows is a logical stretch, but it's an interesting coincidence if nothing else: if the curve is calculated using the arc definition, but the stationing is calculated using 100-foot chords, the curve data given works perfectly.
> ... I know what follows is a logical stretch, but it's an interesting coincidence if nothing else: if the curve is calculated using the arc definition, but the stationing is calculated using 100-foot chords, the curve data given works perfectly.
That's good analysis Jim!
"if nothing else: if the curve is calculated using the arc definition, but the stationing is calculated using 100-foot chords, the curve data given works perfectly."
I don't think so. You're looking at 8 footies here. As far as I can determine, railroads used the chord definition of a curve, and in the 1800's when the line was constructed, they would have used the norm, a chord based set of curve tables and formulas. Calcing the curve out from the P.C. to the next full station, 6229+00 and then on 100' chords to the last full station, 6240+00, the last chord distance to the P.T. is 80.2' = 6240+80.2 for the P.T. station, not 6240+72.2 as depicted on the drawing.
Might I offer the principle of 'Ockham's razor'. Let the simplest explanation prevail. Having worked for UP 25 years ago I know, at that time, tables were still being used - occasionally. But Jims answer is the most probable.
> if the curve is calculated using the arc definition, but the stationing is calculated using 100-foot chords, the curve data given works perfectly.
Jim, I'm not sure how that works out :-S . Arc definition with that degree of curvature & delta still equates to an arc (PC to PT) length of 1237.22'. Unless I'm missing something, I still don't see how the listed PC-PT stationing fit that curve, whether chord or arc definition.
This is considered a "flat curve", 3°, and a chord for a chord (RR) defined curve is 100': for an arc defined curve (Hwy) is 99.99'. There is not a significant difference in chord lengths to make up the 8' difference in Stationing at the P.T. Calc this curve from the P.C. to the P.I. (Tangent = 641.27'), then to the P.T. (Tangent = 641.27'), then calc from the P.C. using distance-distance intersections, 57' chord and radius 1910.08' to station 6229+00, then continuing using 100' chords and 1910.08' radius from Station 6229+00 to Station 6240+00 and then inverse from Station 6240+00 to the P.T you get 80.2'. The rounded arc lengths for the chord defined curve is 1237.2'± and a hwy defined curve is 1237.2'±.
The curve data depicted on the drawing is bogus and has an erroneous parameter.
> Jim, I'm not sure how that works out
It doesn't. In the cold light of day, I find that I did what I'm always chiding my 8th-grade son for doing: not neatly showing my work, then inadvertently grabbing an incorrect figure to carry forward in a calculation. Simply stated: I goofed. Public embarrassment shall be my punishment.
Cautionary note to Paul Plutae and Mapman: Don't believe everything you read!
In the immortal words of Maxwell Smart: Sorry about that, Chief.
Jim
No worries mate!
If everyone that ever posted a booboo on this site was banned, there wouldn't be anybody here!
Loyal