Again article does not have anything to do with dogs, unless you are referring to the author.

Review from last month:

1. Obtain CAD drawing with contour lines
2. Check the contours for correct elevations
3. Convert the contours to points connected by breaklines along the contour line
4. Check the TIN to see if properly linked
5. Check for FLAT TRIANGLES
6. Fix flat triangles with software settings or use breaklines to correct

Listed above are the general steps usually taken to begin the process of convert contours from a project to a 3D Model.

If you get to the point where you have done all of the general settings and you still have issues with the shape of the model, which in most cases you will.  Then you must get even more involved with extra points or breaklines or both.  The process can be very tedious, but the results are a more accurate surface to use on the project.  This can affect several issues regarding the project such as volumes, and profiles.

In Figure 1, it is pointed out that there are still some problems with the stream bed.  This issue can be fixed by adding some strategically place points and breaklines to further control the surface.

In this case let’s add a breakline that continues up the stream bottom, but also drop off a point so that a break line can be added that runs up the second stream bed.

In Figure 2, you will notice that breaklines with extra points have been added to the centerline of the stream beds.  This was not too scientific; I used the elevation of the nose of each contour.  Then I interpolated points along the breaklines to help build a smooth model.

So, now in Figure 3, we see the effects of adding the breaklines with the interpolated points.  The stream bed much more resembles the smooth flow condition that you would find in the field or the intent of a design.  The process is relatively simple, just repetitive.  Going over the entire site and checking the shape of the surface is all a part of the quality process to insure accuracy to the best of your ability.

Another way of analyzing the surface that is different than the use of the 3D views would be to use contours.  In Figure 4, you will notice a couple of things. 

The first would be the density of the contours.  I set the contour interval to .1 foot rather than 2 foot.  I believe this helps you eye to see the relief now that you are looking at a flat, non-3D visual.  For some people it is hard to see the surface changes by just looking at contours (a couple of beers might help). 

The second issue is the blank spots where no contours exist.  This is where the FLAT TRIANGLES exist.  So each time you make a change to the surface to improve its shape, re-contour and check out the results.

Now as you see in Figure 5, the contours show the affects of the breaklines that were added.  The problem of FLAT TRIANGLEs has been resolved.  Once you have finished you would reset the contouring routine to something more realistic like 1’ or 2’ contours for a finished plot.

So, I recommend using every tool your software offers to explore, develop, analyze, and quality control surface that you build for data preparation.  Don’t just run a routine that converts contours to a 3D model and assume that the surface is correct and you can proceed to the next task.  A tremendous amount of finessing occurs to make model correct. 

Building an accurate 3D model is as much of an art as it is engineering.  The design plans in many cases are closer to recommendations for the project as opposed to complete detailed surface definition.  Quite often the spot elevations conflict with the contour lines.  Especially when you are dealing with proposed design.

Remember you are not the designing engineer.  It is not your prerogative to fix major errors in a set of plans or redesign the project so it works.  The best scenario is to have a communication link with the design engineer to determine the actual intent.  If you don’t start the conversation with ‘these plans suck’, you might get some help. 

So until next time, happy modeling.

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