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Creating a DTM from a Contour Map Example

Updated November 13, 2019

This article applies to:
  • Terrain 3D
  • Terrain Forestry
  • RoadEng Civil
  • RoadEng Forestry

It is often useful to create a digital terrain model (DTM) from an existing contour map instead from raw survey data. To check the DTM, we can generate contours and compare them to the original. In most cases, areas where the generated contours differ from the input contours can be resolved by making the some or all of the input contours into breaklines. However, some cases will require additional breaklines. The following example illustrates the problem.

Capture_72.PNG Capture_70.PNG

                Figure 1: Original  Contours                                Figure 2: Generated Contours

Original input contours are shown above as dotted lines in the figure above. When a TIN model and contours are generated the result is shown in the figure below.

The generated contours do not correctly match those from the map. This is caused by flat triangles forming across the nose.


                                                              Figure 3: Flat Triangles 

To correct the problem a breakline is created in the direction of the 'nose' as shown below. Creating this breakline is done after a terrain model has been created as follows.

   1. With the Plan View window active select menu View | Active Window (Plan) Options. Make     sure that Snap to Point is set.

  When Snap to Point/Line is set and an elevation feature is created the elevation will ‘picked   up’ when a point is snapped.

   2. Slelect menu Edit | New Feature. Check Displayed, Connected, Elevations, Modeled, and     Breakline and press the Mouse button.  


Figure 4: Edit | New Feature Dialog

   3. Using the mouse, create the breakline with points located at the original contours as     shown in the figure below.

  4. When the terrain model is regenerated the contours should closely match the original       contours.

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            Figure 5: Breakline Added                              Figure 6: Contours Generated a with the                                                                                                              Breakline Feature