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.

 

 

 

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.