Hi Everyone:
How do you deal with RR curve (chord definition) alignments in C3D? Is there a way to set it up to station utilizing a chord definition in C3D, or do you have to use station equations?
Thanks!
Paul
When I create roadway centerlines I use this procedure:
1. Create the tangents and PI
2. Under the Lines/Curves menu pick Create Curves and use either Curve on two lines (Leaves Tangents intact) or Curve between two lines (Trims Tangents at Curve)
3. Pick tangents.
4. Progam prompts for criteria, pick degree
5. At this point you have two options, just enter a angle in ddd.mmss which uses chord definition, or you can switch it to arc definition, then enter the degree of curve. (follow the prompts on the command line)
after making my linework I define the alignment from them.
Hope this is what you're looking for.
Wendell, If you had a nickel for every time a question pops up about this software, you'd have a nice bit of change by now.
Reminds me of the Big Lebowsky movie "you're entering a wold of pain". Sorry for the hijack.
Anyway, good luck with your question man, and the next ones too!
:beer:
I see at least as many questions here about Carlson... I suppose the big difference is that when there's a question about Carlson, you might see someone from Carlson answer the question. I don't know if anyone from Autodesk even knows this forum exists...
As far as the railroad stationing, if you're talking about that funky stationing that follows 100' chords instead of the actual arc of the curve, then no, there's no built-in way to handle that. You have to resort to "tricks".
I have about 200 plus rail design build proj
The 100 ft coord is the means to describe the interior delta angle
nothing more (its really a measure of the tightness of the curve during trackside Chats)
for example a 13 deg curve is when the 100 ft coord makes a
interior delta angle of the 100 ftcoord of 13deg 00 min oo sec
Stationing is along the arc not the coord
Possibly in the old days of crude survey and drafting the
Cord MAY have been used as the arc length +-+-+
due to long winded calcs
Peter K
Here is the situation. I haven't had a chance to look at it myself, which is why I asked a more general question to get some ideas on what it could be, but my understanding is the following:
One of our guys has been given a railroad alignment. The coordinates look fine. The spiral curves look fine. When he lists the curves using the Arc and Chord definitions in Civil 3d, it tells him that the arc (which hasn't been changed between lists) is 0.03' different, and that difference seems to change based on the size of the curve.
Something sounds fishy to me, since the arc lengths should not change (just the degree of curve). Either C3D's data, our data, or our interpretation of the C3D data is screwy.
If you have a perfect circular curve that is tangent at both ends, it has a unique definition by arc methods, and can be approximately described in RR chord definitions. If your software works that way, you should get a constant arc length. But you need to know what is being held constant when you switch between definitions. Degree of curvature and stationing are only the most obvious differences.
The traditional RR curve layout methods involves approximations from the beginning. If you use the traditional layout methods, you accumulate some discrepancies at the 0.0x foot level that come out as non-tangency or non-circularity, depending on what you hold fixed. If you change the station at PC from X+00 to X+25 to X+50 to X+75 and follow the traditional RR layout techniques, you even get slightly different curves.
Do you want to be tangent at PC and PT and have chords of a perfect circular arc? You have to fudge the layout method to achieve that, because the first and last angle to be turned, and/or first and last chord distances, will not be what the usual layout method uses.
Railroad curves are stationed by chords, not arcs. Refer to Route Location & Design, 5th Edition, page 72, by Hickerson.
Paul - I'm not sure if this is how it words in C3D, but in LDT 2007 a chord definition listing of a curve will give you "arc length" followed by "true arc". The "arc length" is the chorded length of curve and the "true arc" is, well, the true arc length of curve, which will be longer than the listed "arc length".
[msg=54075]Example[/msg]
Thanks Mike - that looks like what I'm looking for.
Everyone - thanks for your help and insight - I appreciate it!
As Mr. Dowdell states, railroad curves are stationed along the CHORD. If you have a polyline in AUTOCAD that is 1000 feet long and begins at 0+00, your end station will most definitely NOT be 10+00.00. The radii of a 1° chord definition and a 1° arc definition curve are different. If your software does not support chord definition, you may have to set coordinate points at every station to define an alignment.
