Spline type strangeness

[ammobake]

So earlier today I was working in Civil3D experimenting to see if there was an easy way to "draw in" a finished ground profile as a spline or polyline and convert it (in the current profile view) to represent the "finished ground" on a road project when I found some interesting stuff I thought I would share.

 

In web searching I found some 3rd party software that can indeed convert a polyline to a new profile in civil3d but I didn't want to go that route.

 

I came across an autodesk forums post about this...

https://forums.autodesk.com/t5/civil-3d-forum/converting-line-polyline-amp-spline-into-a-profile-in-civil-3d/td-p/8221390

 

the answer was that in the "profile creation tools" dialog box there is an option to convert a line or "quadratic spline" to a profile in the view you have selected.  BUT it does not work for polylines - only lines or quadratic splines.

 

Thinking I had this under control, I drew a spline where I wanted finished ground to be for the project and tried to convert it in the profile creation tools.  BUT the command kept failing and I couldn't figure out why.

 

I tried flattening my spline trying to see if that would help, etc..  Wouldn't work.  That's when I came across a really interesting system variable called "SPLINETYPE" that I haven't dealt with in 15 years of CAD Drafting.

 

Apparently there are 2 different spline types in CAD (version 2016 and higher) each with their own built-in programming to control curvature.

 

SPLINETYPE(5) = Quadratic B-spline

SPLINETYPE(6) = Cubic B-spline

 

The main difference is that a cubic spline can be manipulated to twist in space - meaning that a cubic spline can potentially contain data reaching into the 3-dimensional Z or -Z directions.  A quadratic spline is just a flat parabola much like a polyline always stays at one elevation on Z (just depending on where you start the polyline).

 

In my case the default was type (6) which civil3d didn't like.  So Civil3d was specifically wanting a quadratic spline type in order to convert that line to a finished ground profile. 

In thinking about this, it does make a lot more sense now.

 

The program can only use a line or quadratic spline because they can be in-line with the profile view (flat) and then be converted as such.  Since a 2D or 3D polyline can be at a different Z dimension and a cubic spline (default?) can contain information reaching into the 3 dimensional space, the program wants a line or spline that is completely flat and in-line with the profile view you are seeing in Civil3D.

 

Learn something every day I guess.  Happy Friday everyone.

 

-ChriS