I’ve been playing with some ideas, code and Carlson Civil Suite today and I’ve stumbled across an interesting issue with Carlson’s contour routine.
Given this equation for a hyperbolic paraboloid, For more information on this surface
And porting some code to VBA so everyone can follow along
Option Explicit
Public Sub Parabolid()
Dim x As Double
Dim y As Double
Dim z As Double
Dim a As Double
Dim b As Double
Dim pt As AcadPoint
Dim coords(2) As Double
Dim result As Double
a = 1
b = 1
For x = -10 To 10 Step 0.1
For y = -10 To 10 Step 0.1
z = x ^ 2 / a ^ 2 - y ^ 2 / b ^ 2
coords(0) = x: coords(1) = y: coords(2) = z
ThisDrawing.ModelSpace.AddPoint (coords)
Next y
Next x
End Sub
And then triangulating and contouring with these options
Produces a couple of visible errors
After a trial run with the “Reduce Vertices” option turned off the results appear correct, or at least visually correct, I’ve not verified them.
So I’m left wondering why the reduce vertices option produced asymmetrical results.
How many times have you pieced together the spot elevation data on a set of plans, triangulated it and then contoured it only to find isolated areas where the triangulation routine did not quite get it right? I sometimes contour at ridiculous contour intervals searching for any small anomalies that won’t show up on a one or two foot interval but will show up in your parking lot while grading. So I like preparing DTMs and then contouring at an interval of 0.10 or 0.25 feet. This gives me the ability to pick out any hiccups that have resulted in the triangulation routine. Then I can use Carlson’s Surface Manager to manually add or delete any points, to swap edges or to even delete triangles. I was a bit shocked that this excellent tool wasn’t mentioned in any of the sessions that I attend at the recent Carlson User Conference. It works like this:
Once you have a tin file, you start the Surface Manager like this
Or you can click the corresponding icon on the Carlson Surface tool bar, either of which will yield
From here you first, Add a surface then highlight it and press Set Current. You may use the Properties button to launch a modified Triangulate and Contour dialog to setup how your surface will be treated on the screen. Pay special attention to the “Draw Slope Arrows” option, it can be a lot of help.
Now using these menu options, Add Point, Remove Point, Remove Triangle, Set Point Elevation, Swap TIN Edge and Add Breakline, you can tweak away at your tin, dynamically!
There isn’t a toolbar provided for these options but one is easily enough made, and if you pay attention to the command line you can pick-up a few other neat tricks.