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Setting Up a Linear Corridor Feature

Updated October 18, 2017


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

Now you will read in a proposed center line and later use it to create an area of interest.

  1. Home | Insert File button.
    • Browse for file <Terrain>\LiDAR\ ProposedAlignment.SHP.
    • Press Open button.
    • The Import options dialogue box below appears.

Figure 1: Import Options Dialogue Box

  • Press OK, Softree Warning stating “Incoming coordinate system and unit are undefined. OK to continue without conversion?”. Check box “Do not show this message again”.
  • Press Continue to load the proposed center line shown below. The reason for this is the coordinate system and units in empty.terx are correct.

Figure 2: Softree Warning Message

  1. Now that the road center line has been brought in, we can bring in the LIDAR data. This example only contains approximately 700,000 points to save download and file read time. In the following steps, we will read in the data at full resolution in the area of interest (AOI) and skip some points outside this area. In addition, we will follow some important guidelines to prevent slow draw times and memory overload.

Figure 3: Proposed Road Center Line

  1. Home | Insert File button.
    • Select All Supported Files from dropdown list and highlight both .txt files included with this example. <Terrain>\LiDAR\

Figure 4: Inserting Multiple LiDAR files

  1. Select ASCII Lidar (x,y,z) if prompted with a Select Option dialog. Press OK.

Note: Using Home | Insert File button unlike File | Open that allows multiple files at once and does not clear existing features from your Terrain.

You will now be presented with the import options (in case you want to make last minute changes).

  1. Click the Test tab then Next Record button a few times to see what the file looks like.

Note that the X, Y, Z fields are showing the correct values (figure below). This indicates that the options sets in the Structure tab are working correctly.

Figure 5: The Test Tab After Pressing the Next Record Button a Few Times

Note: Memory Usage / Display Speed Guidelines

Other Import Options have been setup to avoid using more memory than necessary and to make the resulting Terrain display manageable. The following rules are necessary when importing large data sets:

a) Do not attach comments or other attributes to every point.

b) Do not allow very large numbers of points in features.

c) Do not make every point into a separate feature.

d) Do not attach symbols to every point.

e) Do not turn on labels (such as Elevation) that will display at every point.

If you use the standard LiDAR import options these guidelines will be taken care of for you.

  1. Click on the Structure tab. Notice that there are no Attributes defined in the Column Assignment section (Rule A).

Figure 6: The Structure Tab Defines the Location of the X,Y,Z Coordinates

  1. Structure tab | Features… Check Limit size of Features, Set Max points per feature: 1024. Press OK to close.

Figure 7: Feature Size is Limited to 1024 points

  1. Code tab | Set the following fields:
    • Type: Polyline
    • Feature Creation: Connect All
    • Connected: No (dropdown).
    • Also note that no symbol is defined (rule D above). In some cases, it makes sense to turn off the Displayed property, to speed draw time later.

Figure 8: Point Code Properties Suitable For Large Data Set Import

Thinning Data on Import

There are now 3 different point-thinning options available in the Terrain module. This example will detail thinning at the time of import. When possible, it is recommended to use the two other methods (detailed later in this chapter), as they both result in more accurate surface representations.

  1. Click on the Selection tab to show the options below:

Figure 9: Selection Options

  1. Press Add... to open the Filtering Region options as shown below.

Figure 10: Filtering Options

  1. Select Corridor (shown above). Then press Select…
  2. This dialog allows you to specify features (rectangles, corridors or polygons) to filter around. Double-click on the alignment feature “ProposedAlignment-0”. Press OK.
  3. Set the corridor width to 200. Press OK.

Refer to figure below:

Figure 11: Defining a Corridor with a Linear Feature

  1. Select Default in the list and set the Point Resolution to 9:

Figure 12: These Setup Options will Skip Most Points Outside of Corridor-1

  1. Press the OK button to read the data.

It will take a couple of minutes to import about 69,000 points out of the 680,000 available.

Figure 13: Full Point Density Along a Corridor, Reduced Density Outside

Thinning Data After Import

With Version 8, there are three new methods of thinning (simplification). The first two of these result in a more accurate surface representation than the thinning options on import:

  • Basic Grid Simplification (fast): This thinning method is based off a defined grid size. One point per grid is retained. The Calculate button in Point counts can be used to quickly determine the % reduction of points.
  • Closest Point Removal (slow): This thinning method utilizes both a minimum distance and a defined sample grid size. Multiple points per grid can be retained if they are further than the minimum distance. In the figure below, the minimum radius is represented in the first grid cell by the green circles. Neighboring points within the cell that fall in the radius are removed. This method is considerably slower than the basic grid. We recommend setting a radius smaller than the grid size.
  • Remove all points: This thinning method removes all points. It is useful for removing wanted points that fall outside areas of interest (Excluded regions).

Figure 14: Thinning Methods

We will start by opening the previous design with shape file and LiDAR already imported, but in full resolution.

  1. File | Open <Terrain>\LiDAR\Thinning After.terx

Figure 15: Thinning After.terx

  1. Terrain Modeling | Simplify. This will open the Simplify Surface Point Data dialog.

Basic Grid Simplification (fast)

We will first explore basic grid simplification.

  1. Ensure the Method is set to Basic Grid Simplification (Fast). Set the Sample Grid Spacing set at 20.00.
  2. Under Excluded Regions, press Add.
  3. Select Corridor (similar to how we thinned on import in the previous example). Then press Select…
  4. This dialog allows you to specify features (rectangles, corridors or polygons) to filter around. Double-click on the alignment feature “ProposedAlignment-0”. Press OK.
  5. Set the corridor width to 200. Press OK.
  6. Press Calculate.

Your dialog should now look like the figure below. Under Point Counts you will see that our settings will result in a 74.1% reduction, but the area within the corridor will remain in full resolution.

Figure 16: Basic Grid Simplification

  1. Press OK to proceed with the thinning.
  2. Press OK when prompted with the warning message: “Warning there is not enough space to UNDO this operation. Do you wish to continue?”

Figure 17: Basic Grid Thinning Results

The total point count of our surface has been reduced to 149,376 from the original 576,152.

  1. File | New. Do not save changes.

Closest Point Removal (slow)

We will now see the impact Closest Point removal.

  1. File | Open <Terrain>\LiDAR\Thinning After.terx
  2. Terrain Modeling | Simplify button. Ensure the Method is set to Closest Point Removal (Slow). Set the Sample Grid Spacing set at 20.00. Set the Minimum Distance at 10.
  3. Under Excluded Regions | Add… | Select Corridor | press Select…
  4. Double-click alignment feature “ProposedAlignment-0”| Press OK.
  5. Set the corridor width to 200. Press OK.

Your dialog should now look like:

Figure 18: Closest Point Removal Setup in Dialog

  1. Press OK to proceed. Press OK when prompted with the warning. The screen now displays the thinned points.

Note: Unlike the fast method, the Closest Point removal method cannot estimate point counts from within the dialog. Press OK to proceed with the thinning.

Figure 19: Basic Grid Thinning Results

The total point count of our surface has been reduced to 155,398 from the original 576,152.

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