Hi there,
I am a civil engineer who uses Rhino and Grasshopper as my favourite tool in my everyday work life.
Something has been frustrating me lately, and I’ve come here to see if any of you geniuses has a solution.
When describing the geometry of roads or rail roads, the industry standard is to have separate descriptions for plan data and elevation data. Se example below (please excuse the Swedish, I hope it makes sense):
Straight lines, arcs, and sometimes clothoids are combined to create the geometry.
In 2D this is all fine and dandy, it’s easy to just use this information to make perfect NURBS curves to describe the geometry.
However, when you want to combine these to sets of data into one 3D curve it gets tricky. Intersection points between curve segments do not coincide between plan data and elevation data. The typical way to do this is to calculate the coordinates for discrete parameters with even spacing, and then make a polyline or interpolated curve between the points.
This has implications. If you choose to make a polyline, accuracy is lost. Bridges etc. often need accuracy down to the millimeter. If you choose to make an interpolated curve, things get computationally heavy. Making huge sweeps or lofts based on interpolated curves is not practical.
Is there a way to make 3D NURBS curves with a perfect mathematical definition as described above?
Meaning for example an arc leading in to a line segment in plan view, with an arc in elevation?
Please feel free to ask for further explanation if this does not make sense.
