I have to scan a 1/4 mile section of toll road, and was given as-built plans. Part of the scope is to recover existing control. The plans show copperweld pins set at some of the PC, PI, PT, and at some random POT's. There is a table with coordinates (NAD83 (1986) I believe) of the PC's, PI's, PT's, TS's, SC's,?ÿ CS's, and ST's. So I need to compute coordinates of the reference pins to try and recover some. The sketch shows the survey & construction baseline (centerline of the highway) with angle and distance to pins. The one that is in the section I am working on is at a PI. But, it is referenced off of the PI station on the curve, not the PI on the tangents. So how does one backsight along a curve??ÿ
In a separate note, it says that the stationing on the BM is the same as the PI station. So it is on the line from the radius point through the PI. But I can't figure out where they get an angle of 263?ø00'00". By definition it is 270?ø from the curve. If I use the PC back (which is how it is drawn), I get an angle of 265?ø17'17", if I use the PT ahead, I get an angle of 92?ø00'00" (i.e. 268?ø00'00" left angle). Curve radius is 11459.16 feet (0?ø30'00" degree of curve), no spiral.?ÿ
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What am I missing??ÿ
As-builts are stamped by an engineer, not a surveyor...maybe that is my answer.?ÿ
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What's the rest of the curve data?
I would say the station just references the P.I. of the baseline and not a station value of the benchmark.?ÿ It would be 263?ø from the back tangent to the mark and the reference copperwelds are 264?ø from the benchmark to the P.I.
The plan stamp is rubber. I've seen lot's of 8's mistaken for 3's.?ÿ The chance that it is 90?ø to the curve is slim based on experience. We often have had better luck finding the reference points using a cloth tape for swinging a dist. tie then checking the data.?ÿ
Thanks for this, this is FS study material Gold!
the PC's, PI's, PT's, TS's, SC's,?ÿ CS's, and ST's.
What do TS SC CS & ST stand for, please?
Amen, Brother Ott.?ÿ I avoid spirals like I avoid uni-sex restrooms with no locks on the doors.
I agree.
John, I think you have to go find it and find out where it really is. Base your calcs on what you have should get you pretty close.
@one-cup-o-joe yeah, pretty sure I can find it. Problem is I need to compute coordinates to tie in to.?ÿ
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This agency always has reference mons like that dating back to the 1940's. Not sure why they don't just list the coordinates of the mons, they only list the coordinates of the centerline stations
I just cogo'd out some 1970s highways plans full of spiral curves about a month ago, and if I don't see anymore of that for another decade or two... I won't complain.?ÿ Hah
