Degree of curve or degree of curvature is a measure of curvature used in civil engineering for its easy use in layout surveying.
A n-degree curve turns n degrees over some agreed-upon distance. The usual distance is of chord, but of arc is also common, and other lengths—such as 100 metres where SI is favoured, or a shorter length for sharper curves.
The is a station, used to define length along an alignment. Annotated as 1+00, 2+00 etc.
Typically roads are defined in arcs, and since rail routes have very large radii, the are laid out in chords, as the difference to the arc is inconsequential.
Beware though, the degree of curvature, as typically defined in civil literature, is for a 100' chord.
Note the variation in usage among these samples.
- http://www.fairview-industries.com/standardmodule/circurve.htm *http://ceprofs.tamu.edu/rbruner/curves/circularcrvs.htm