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Several years ago, in my final semester at East Tennessee State University, I had some free hours so I took Calculus III for laughs. There were times that I paid a lot of attention and learned a lot under Jeff Knisley, there were also a lot of times that I was distracted by the computer at my desk, the internet is such a means of escape. Regardless of my study habits at that time I did walk away with a better understanding of surfaces and I still find myself looking back at my notes. Although those notes have holes where my attention was elsewhere, lucky though you can find the course material available to everyone at http://math.etsu.edu/multicalc/ Give it a look, it is worth your time.

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.

That last post got me to thinking, “What happened to Randall Rath?” Why didn’t we do a better job with VB Design and CAD Vault? The core members, of which I was one, could have done better, but we were complacent with the fact that Randall and Ralph would always take care of us. Randall and Ralph gave us so much and asked only that we gave a little in return. We failed both of them and ourselves.

Outside of the Southwest Espresso User Group meeting in Phoenix a few years back this was my first user conference. I came here expecting to be blown away like Randall Rath blew my mind every time I saw him speak. I expected to meet people who would make me take a long look at the quality and procedures that I employ in daily practice. I wanted to be presented skills and methods beyond which I can develop on my own. I wanted to be presented ideas and questions that made me stare at the ceiling, like Randall did in the Little Rock VBA class. I wanted to be shown things that weren’t in the manual or the help files. I wanted to be showed how to make Carlson’s Civil and Machine packages perform to levels beyond which they are advertised to, like how Randall made AutoCAD sing every time I saw him write any code for it. I’ve been disappointed. I find my skill level to probably be on par with the instructors that I’ve had. Short of small time saving tricks I feel like I’m left a bit disappointed.

Not that this User Group Conference didn’t have it’s up sides. I did walk away with more than I arrived with. Maybe I was expecting too much. Maybe the people at Carlson have done their job to well. Maybe the greatness of their software has become mundane to me over the years in which I have used it. I don’t doubt for a minute that there was a lot of people present who walked away satisfied, maybe I was just wanting something unrealistic. Maybe the Carlson manuals are too good, maybe they do express the completeness of the software’s capabilities. All in all though, this was their first event and if they have another I’ll be there.

Now a bit more detailed picking…

Overall I am really concerned with the trivial nature by which the presenters threw data together on the screen and said this is a finished model. I’ve been down that path, when you start blindly triangulating data and pushing it to a machine you get errors.

In the “Surfaces” class in which I sat the presenter made a point of saying “…contours should be treated as output, not as input.” I agree with this statement on the surface, when solid design data is present, I feel as the contours are there to give an instant visual representation of the site and that the contours should only be used as a means of ‘checking’ one’s self. On the other hand though, when contours and spot elevations are the only data present I feel that they can not be ignored.

In one presentation, the presenter showed a drawing consisting of spot elevations along the curb and contours though out the site, no other design data. The presenter then proceeded to show off Carlson’s very savvy text to elevation commands, and built the model from this data. When asked if this was a valid machine model the presenter replied in the affirmative. I never saw him put the contour data in the data set used to create the model, may be he did and I missed it but I was left thinking “What if that data reflected a vertical curve in the parking lot?” Not that he lied when saying it was a valid model, it was, No doubt about it, but was it correct?

Now I plan to read through the conference CD and see what nuggets of information might lay in wait.

Let this post be a preliminary post of the Carlson User Conference, Day One, construction tract. Perhaps I’ll post a more detailed review later.

At the onset of today’s introduction it was revealed, as I posted earlier, that Carlson is moving to support the Intellicad platform while maintain support for the AutoCAD and AutoCAD Map products. Furthermore, Intellicad will ship with the Carlson packages and can be installed side by side with the traditional Carlson AutoCAD Add-on. The only minor catch is that the setup routine will have to be executed twice; however another license will not be required.

Secondly, it was stated that this conference was going to be about learning and not about marketing and sales but I’ve found most of the presenters boasting about their products. This is fine; they have some nice routines and deserve the right to be proud and really are not trying to sell them.

For Session I, I set in on the Surfaces class which stated “We will show varying types appropriate for creating surfaces…” Which I had hoped was more than Points, Lines, 2D Polylines at Elevation and 3D Polylines but I was disappointed. I wanted to ask what was in the header of their ‘.tin’ files but I let the urge pass, I’ll figure it out when I get the time.

The 3D Models Data Prep: Residential & Commercial classes mainly overlapped and mainly covered the text to elevation and polyline editing commands. I was hoping that a technique superior to generically triangulating this data would be presented, but was disappointed again.

Overall I’d rank day one as fair. Personally, the most informative thing today was the text to elevation and Polyline editing commands. Also the brief SiteNet demonstration by Bruce Carlson in today’s final session was very informative; to be the President of the company Bruce has a very detailed knowledge of how his product works.

Tomorrow I am looking forward to the RoadNet, SiteNet and Machine Control sessions.

Bruce Carlson just announced that the new Carlson Civil Package will ship with Intellicad 6.4 while still supporting AutoCAD.

Seems I have gotten ahead of myself, I have started posting about things like DTMs and TINs and I have not attempted to explain what they are. For starters, a DTM is a Digital Terrain Model and a TIN is a Triangulated Irregular Network. For the most part, I often use the terms interchangeably but there is a minute difference. Both terms represent a surface, a composition of plane segments that represent and model the shape of the earth. Both compositions contain points, connected by line segments, line segments that define edges of triangles. Adjoining triangles share both vertices and edges; the vertex of one triangle cannot lie in the interior of another triangle.

The difference lies in the orientation of the points; a DTM is most often affiliated with designed surfaces while a TIN is often associated with field collected data, hence the irregular-ness.

Occasionally I encounter a set of grading plans with nothing but contour lines as a guide to building a site. Seldom, if ever, does contour lines provide sufficient data to properly establish an accurate DTM from which to work. Allow me a chance to illustrate:

Looks simple and straightforward does it not, put a little more thought into it. A section from a not so arbitrary, direction wise anyway, baseline yields this section :

What are the odds that the design engineer actually intended to break the –2% slope to –2.8%? Or is it more likely that the -2% was intended to strike the 2:1 slope? In this example the later is the true statement.  Then why does it show the change in grade? Simple, the contour interval is set at 1-foot, so with a 2% slope there are only two contour lines generated every one hundred feet. Anything that happens inside this interval is not propery represented by contour lines. Just one example why the design engineer should always include alignments and typical sections.

An area in which I place a great deal of thought these days is in machine control systems. Particularly those systems that are used as grade control for earth moving equipment, such as for dozers, excavators and road graders. This systems function using

1. Some type of positioning systems (usually GPS or Robotics)

2. Device interface (with or without hydraulic interfaces)

While this is an over simplification of the systems it serves the purpose of this introductory post, as the focus of this post is not on the systems themselves but rather the data, models, they consume.

The system with which I work daily is a product of Carlson Software. The machine mounted software is title Carlson Grade. Hats off to Carlson on their current product line-up, they are made right. All of the data files produced on one product are directly movable to their other software. So files created on the desktop platform are usable with their data collectors and their machine control systems. Nice.

 I have heard various arguments about what should be contained in a final and complete Digital Terrain Model. Some may argue that break lines and spot elevations need to remain in the final file. I don’t agree, neither does Carlson. I am of the opinion that the final DTM file should only contain defined planes and surfaces, no breaklines and no spot elevations. The edges of the plane segments should follow the breaklines, no need in storing redundant data.  

Carlson has two dtm files structures. The older of the two has the file extension .flt and it is a txt file containing triangle edge data. The newer and faster format has the file extension .tin and is a binary file containing vertices and triangle data.

I spend a lot of time interpreting civil site plans prepared by others and then building DTMs or TINs from them. As time goes on I hope to post a few tricks and approaches that I have found useful.