Line of Sight Tool

The Line of Sight tool provides a visual indication of whether specific locations in the 3D World can be seen from a selected position. The tool displays a visual marker for the existence of a line of sight from a single observer position to multiple positions in the world.

This feature takes into account the observer’s viewpoint, direction of sight and distance of sight, to portray which locations can be viewed from the viewpoint, and which locations cannot be viewed. The observer and target positions can be set at any altitude above the terrain.

Using the Line of Sight Analysis Tool

To use the Line of Sight Analysis tool:

1. On the Analysis tab, in the Line of Sight group, click Line of Sight.

2. In the Line of Sight Analysis property sheet, enter the following parameters:

a. In the Analysis section, in the Sampling Interval field, enter the desired value for the sample resolution of your measurement. This value represents the distance between terrain samples for the measurement along each line. A smaller sample size is more accurate but slower to calculate.

b. In the Observer section, in the Height field, enter the desired value for the altitude of the observer.

Note: The X and Y observer position fields in the Observer section are derived from the point you select in the 3D Window (see below). They only become enabled after you place the Observer point, so you can modify the values as required in the property sheet.

c. In the Targets section, in the Height field, enter the desired value for the altitude of the target point or points.

3. Once you have set the necessary parameters, click the cursor to define your viewpoint for the observer.

4. Click in the 3D Window to place the target points. You must place at least one point in the 3D Window.

5. Right-click to finish the operation. At this point, TerraExplorer Pro begins to calculate the line of sight. This process can take a few seconds.

6. Once the Line of Sight Analysis has been completed, you can edit the parameters and recalculate, or close the property sheet to finish the operation.

Once completed, a single line, or group of lines, marked on the terrain appear between the viewpoint and the endpoint. Target points that are visible from the observer viewpoint are colored green, whereas points that are not visible from the observer viewpoint are colored red.

Note: To perform another line of sight measurement, you must first close the property sheet either by clicking Close on the property sheet, or by clicking again the Line of Sight command on the Analysis tab.

Line of Sight Property Sheet Parameters

Object Parameter	Activity
Observer All the fields in this section except Height are only enabled after the Observer viewpoint is selected in the 3D Window.
X	Enter the X-coordinate for the observer position. Change this value to move the observer position.
Y	Enter the Y-coordinate for the observer position. Change this value to move the observer position.
MGRS	The coordinates of the observer position in Military Grid Reference System (MGRS) coordinates. This field is only available if Show MGRS Coordinates was selected in the Options dialog. See “View” in the “Using TerraExplorer Options” chapter for more information.
Height	Enter the desired value for the observer altitude.
Targets All the fields in this section except Height are only enabled after the Target points are selected in the 3D Window.
Selected Point	Select which target point’s position you want to edit.
Target X	The X-coordinate for the target position.
Target Y	The Y-coordinate for the target position.
Target MGRS	The coordinates of the target position in Military Grid Reference System (MGRS) coordinates. This field is only available if Show MGRS Coordinates was selected in the Options dialog. See “View” in the “Using TerraExplorer Options” chapter for more information.
Target Height	Enter the desired value for the altitude of the target point (or points).
Analysis
Sampling Interval	Enter the desired value for the resolution of the measurement. This value represents the distance between sample points along each line. The smaller the sample interval, the more accurate the measurement, but the longer it takes to calculate.
Recalculate	Click this button to perform the calculation again with the updated parameters.
Appearance
Name	Type the description or name of the Line of Sight. This text appears in the Project Tree as the name of the object.
Activation Action	Select the action to perform when the object is selected from the Project Tree.
Timespan
Start Time	Click Edit and select the date and time when the Line of Sight should first become visible.
End Time	Click Edit and select the date and time when the Line of Sight should stop being visible.
Visibility
Default Viewing Distance	Determines the viewing distance of the camera from the Line of Sight observer position. This distance is used as a stop mark for any “Fly-to” or “View Object” operation. It is also used when editing the object from the Project Tree. When this value is set to the default of -1, TerraExplorer calculates and sets the ideal viewing distance based on its size.
Max. Visibility Distance	Sets the maximal distance from the camera above which the Line of Sight disappears.
Min. Visibility Distance	Sets the minimal distance from the camera below which the Line of Sight disappears.
General
Show in Viewer	Determines if the Line of Sight appears in the Project Tree when the file is viewed with the TerraExplorer Basic viewer.
Message	The message associated with the object. The number displayed is the number of the message. To create a new message, or update an existing message, open the Create Message dialog by clicking in this field and selecting Edit. See “Using the Create Message Dialog” in the “Working with Objects” chapter for more information.
Tooltip	Type a tool tip to appear when the mouse cursor is placed over the Line of Sight in the 3D Window.