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2D and 3D Features

Updated October 18, 2017


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

Stream Survey Example

A 3D feature has elevation (Z) values explicitly defined at each point (X, Y). A 2D feature, on the other hand, does not contain elevation data.

There two kinds of 3D feature:

  • 3D modelled (3D): Points contain elevation values that are used by Terrain to create the DTM surface (for example ground survey points).

  • 3D not modelled (3d): Elevations are defined but not used in the surface model (for example the bridge deck points).

There are also two kinds of 2D features:

  • 2D draped (2D): The feature points can pick up the elevation of the DTM surface. If there is no surface under a point it will have an undefined elevation (-9999). A draped feature will create a profile (or cross section) of the surface wherever it is placed.

  • 2D not draped (2d): Elevations are always undefined (-9999).

The concept of 2D versus 3D features is simple but has several subtleties with important consequences. The next example investigates the properties of 2D and 3D features.

To follow the example the Mapping and Drafting, Surface Generation and Contouring, Profile Window, and Profile Drafting and Design function groups must be enabled.

  1. File | Open. <Terrain>\Profile\topograph.terx

This is the same example used in the previous exercise, see first figure in the “creating a profile” exercise above.

  1. Select the thick blue feature (Stream-2) by clicking on it with the selection cursor .

  2. The name and type of the current selected feature is displayed in the lower right corner of the screen: Stream-2 (3D~). This indicates that the current feature is 3D modelled; it is incorporated into the surface. The ~ symbol indicates the feature is a breakline. (See Digital Terrain Modeling for information about breaklines).

  3. Open the Feature Property Panel.

  4. The Feature Properties panel allows you to modify all properties (including the feature Name). Notice that both the Elevations and Modelled checkboxes are selected.

Figure 1: Feature Properties Panel

Now we will create a draped feature for cross section display.

Note: A draped feature has only X and Y coordinates the elevation Z of the feature comes from the existing terrain.

  1. Plan | New Feature. This opens a feature properties dialogue box.

Note: If there is a feature selected, the feature created with Right-click | New Feature… will inherit the current feature properties.

  1. Change the Name to Cross Section.

  2. Uncheck the Elevations check box (this also clears the Breakline property).

  3. Press the Create using Mouse button to close the dialogue box and begin creating points with the mouse.

  4. Draw a feature with two points somewhat perpendicular to the stream (similar to that shown in the figure below).

  5. Right-click mouse and choose mode Select with Mouse.

Figure 2: 2D Feature Across the Stream

  1. With the cross section feature selected, View | New Window | Profile button to view a fence section of the feature.

Figure 3: 2D Draped Feature Cross Section Depicts the Ground Elevation

Notice that the Profile window shows the ground surface between the two end points. These new points are called TIN points and they show the elevation of the underlying DTM. They are automatically inserted in 2D draped features wherever a triangle side is crossed.

Note: TIN points cannot be edited. They can, however, be labeled if you set the TIN Points check box in the Profile window options.

Stream Survey Example Continued

It is possible to drape a feature on multiple DTM surfaces. To do this, one or more Digital Terrain Models (DTM's) must have been created in separate terrain files. These files can be then displayed as background terrains in the Plan and Profile Windows.

For this example, two DTM’s have been prepared, overburden.terx and overburden1.terx (separating two overburden layers). These surfaces will be set as background terrains and the profile will be draped on them.

To add background files:

  1. Profile | Profile Options (also available in the right-click context menu) to open the Profile Window Options dialogue box.

  2. Ensure Background is enabled and press the button to open the Background Display Files dialogue box (figure below). Press Add… and choose <Terrain>\Profile\overburden.terx and press OK.

  3. Repeat for <Terrain>\Profile\overburden1.terx.

Figure 4: Adding Background Files

  1. You should still be in the Background Display Files dialogue box. The next two steps set the color and hatching for each layer.

  2. Select file overburden.terx and press the Properties button.

  3. Within the Background Display Properties dialog, select Profile Feature Format button and set the color to green and hatch type to dots 2.

Figure 5: Configuring Background Surface Format.

  1. Press OK twice to return to the Background Display Files dialog.

  2. Repeat for overburden1.terx (choose your own color and hatch type).

  3. Press OK until you have returned to the main screen.

Your Profile Window should now appear similar to the figure below.

Figure 6: Profile Window with Multiple Layers

  1. File |New. Do not save the changes.

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