TECHNICAL TIP ~ InRoads DTM Conflicts, Part 3



The InRoads surface contains 3D data, or Features, and the resulting triangle network formed by that 3D framework. This concept should be rock solid in your mind. (As well as the 6 basic InRoads Point Types that are used to form InRoads surface models.)

A problem in a surface would be the occurrence of "something" that would either alter the actual 3D data (Features) inappropriately, unknowingly, or unexpectedly, or that would cause the resulting triangle network to form in such a way as to incorrectly represent the existing or proposed surface model. Therefore, a valid problem would ultimately be any situation that could take place where the triangle network was incorrectly forming based on the 3D data that composed it.

How can this happen?

The simplicity of it is that it happens because the feature data in a surface (existing or proposed) has introduced a "conflict" at one or more X, Y (Northing / Easting) locations. This was discussed in the earlier section. Now, here is the root of the problem from a software perspective. If the existing or proposed surface has features in it that present conflicts with other features, InRoads will do something about it whether you want it to or not. This was designed this way by the software developers so that InRoads could accomplish its triangle formation task when it encounters these problems. In the past the software would just 'lock-up' when it hit these problems, so this automated 'repair' is a better option in the grand scheme of things (more on this later).

So what exactly constitutes a problem in the Surface? Here's my technical definition: It's when InRoads has to interpret a situation where the 3D surface data produces a conflict, and that programmatic interpretation results in an incorrect formation of the triangle relationships, thereby producing an invalid representation or an incorrect simulation of the existing condition or design intent.

Keep in mind that this category of surface problem is not taking into account that the actual "design" of the site may be poorly defined by the 3D data. This is an entire separate topic called ... "how to build surfaces with InRoads". And actually sounds like a good topic for the future because most surface 'errors' could be avoided with better attention to detail and higher quality surface data inputs.

Okay, let's look at some real-world examples of instances of surface problems that can crop up from either an existing or design surface perspective. Please don't get hung up on the fact that these surface 'problems' are due to the quality of the data because this is often the case. The focus here is on the fact that InRoads will see these instances as a 'problem' with the surface.


  1. A concrete pad exists behind the sidewalk and this information is being collected by Survey. A conflict could exist when the shot taken at the corner of the concrete pad creates an overlapping breakline with the breakline that represents the back of the sidewalk.
  2. A curb and gutter is being collected by survey and the gutter line (flowline) conflicts with the face of curb.
  3. The start of an edge of pavement has a conflict with the end of the pavement edge when survey collected the first edge of pavement one day and restarted the edge of pavement another day.
  4. The edge of a road that is cutting down the side of a detention pond has a conflict at with the bottom of the pond edge.
  5. The top of a retain wall has a conflict with the toe of the retaining wall.
  6. A road edge from a secondary road, developed from the road cross slope, conflicts with the edge of pavement of the main road where they intersect.

There are many, many examples of design or collection scenarios that could describe conflicts that could be found in a surface model.


Upcoming - ZI Issue 84: How do I locate a Surface problem?

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