Linear and Radial Line of Sight in ArcMap - Dunnett

Linear and Radial Line of Sight in ArcMap Introduction This TI is unofficial and should be used as a guide only. There is an assumption that the user has a general knowledge of how ArcGIS works and the concepts behind line of sight theory. This TI was compiled using the ArcGIS help file, world wide web and creator knowledge, if any errors are discovered correct them as needed. General Knowledge Line of sight (LOS) in ArcGIS is a graphic between two points that depicts where the observer can and can not see. ArcGIS uses several symbols for clarity (see figure 1): Red line – non-visible area Green line – visible area Black dot – observer location Red dot – target location Blue dot – obstruction point

ArcGIS offers two types of LOS: linear line of sight (LLOS) and radial line of sight (RLOS). Both types work off of a DTED or a surface raster data set. For this TI the process will be explained using the Military Analyst Toolbar. If it is not readily available on the ArcMap toolbar. This analysis must be done in data view. It is important to remember that the accuracy of the elevation data and the addition of vegetation and man-made features to the bare earth will affect the field of view of the observer, a field check must be completed to compliment the LLOS and RLOS analysis.

Linear and Radial Line of Sight in ArcMAP Cpl Melissa Dunnett

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Linear Line of Sight (LLOS) LLOS is a LOS between two points, the observer and the target. Once each is identified using the Military Analyst, a graphic line is drawn depicting which areas are visible, which are not and any obstruction points in between. LLOS Instructions1. Ensure that ArcMap is opened with the DTED or raster data set required and that Military Analyst is available to be used. (For this TI LLOS.mxd containing a hillshade and dem has been provided, see figure 2)

Figure 2: Step One, Start Position Screen Shot


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2. To compile a LLOS click on the Military Analyst drop down menu and select the Linear Line of Sight option. (see figure 3) Ensure the correct layer is select in the Military Analyst toolbar, for this tutorial it will be “hillshd2”.

Figure 3: Step Two, Select Linear Line of Sight

3. The Linear Line of Sight window will open up (see figure 4). Ensure the correct input surface is selected in the top drop down menu, for this tutorial it should read “hillshd2”. Click on the top red push pin to begin to select co ordinates for the start position, hereon referred to as observer. An new window menu will open in the ArcMap window between the table of contents and the data view window, this will be referred to as the Coordinate window(see figure 5).

Figure 4: Linear Line of Sight Window with Start Position Push Pin Highlighted

Figure 5: Start Point Coordinates Window

4. There are two methods to select a start point position.

Method One: The mouse can be moved over the map, when it is directly over the desired position left click to choose that position. When the mouse is over the map it will change into crosshairs. Once the left mouse button is clicked the coordinates are recorded in the LLOS window. Once this is complete, the offset can be applied manually in the Linear Line of Sight window, below the Start Point Parameters. See figure 6 for visual clarification.


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Figure 6: Choosing Start Position Using Mouse/Cross Hairs

Method Two: The coordinates can be directly inputted into the Coordinates window.

They can be entered in as Lat/Long, DMS, UTM or MGRS. Once the coordinates have been entered, ensure the correct Datum is selected (it is recommended that the Draw Point Graphic/Feature and Center Display on Coordinates boxes are also selected) click on the convert button. The coordinates will be updated in the LLOS window. Once this is complete, the offset can be applied manually in the Linear Line of Sight window, below the Start Point Parameters. See figure 7 for visual clarification.

Check desired boxes

Click convert

Enter Datum

Enter Coordinates

Figure 7: Choosing Start Position By Manually Entering 5. To select the endpoint parameters, simply click on the bottom red push pin and follow the same steps as for the start point parameters.


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6. Once both the start point and the endpoint parameters are both selected the apply button on the LLOS window will become selectable. Click apply.

Figure 8: Step 6, Click Apply


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7. Once apply is clicked, the application will run its process. A LLOS profile will open up (see figure 9). After viewing this, close or reduce the window to view the data window, which will now display the LLOS graphic (see figure 10). Also, notice the data that has been created in the table of contents.

Figure 9: LLOS Surface Profile

Figure 10: LLOS Graphic, New Table of Contents 8. In the table of contents a Linear Visibility will be displayed. It is numbered so that multiple LLOS can be created. Note: Green line (F) is visible to the observer and Red line (T) is not visible.


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Radial Line of Sight (RLOS) RLOS is a LOS radiating from one point outward in a predetermined radius, it includes all points within the radius and the observer’s field of view. Multiple observers can also be used to determine which areas in the intersecting area are either visible to both or not visible to both. RLOS Instructions 1. Ensure that ArcMap is opened with the DTED or raster data set required and that Military Analyst is available to be used. (For this TI RLOS.mxd has been provided, see figure 11)

Figure 11: Step One, Start Position Screen Shot


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2. To compile a RLOS click on the Military Analyst drop down menu and select the Radial Line of Sight option. (see figure 12) Ensure the correct layer is selected in the Military Analyst drop down menu, for this tutorial it will be “hillshd2”.

Figure 12: Step Two, Click on Radial Line of Sight

3. The Radial Line of Sight window will open up. (see figure 13). Ensure that the correct input file is located in the top drop down box. For this tutorial, it will read “dem2”.

Figure 13: Step Three, Radial Line of Sight Window


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4. To set the coordinate parameters for the Radial Visibility is similar to the LLOS. Click on the red push pin to begin to select the coordinates for the observer. A new window menu will open in the ArcMap window between the table of contents and the data view window, this will be referred to as the Coordinate window (see figure 14).

Method One: The mouse can be moved over the map, when it is directly over the desired position left click to choose that position. When the mouse is over the map it will change into crosshairs. Once the left mouse button is clicked the coordinates are recorded in the RLOS window.

Figure 14: Step Four, Setting Coordinates Using Mouse/Cross Hairs

Method Two: The coordinates can be directly inputted into the Coordinates window. They can be entered in as Lat/Long, DMS, UTM or MGRS. Once the coordinates have been entered, ensure the correct Datum is selected (it is recommended that the Draw Point Graphic/Feature and Center Display on Coordinates boxes are also selected) click on the convert button. The coordinates will be updated in the RLOS window. (see figure 15 for visual clarification)

Click convert

Check desired boxes

Enter Datum

Enter Coordinates

Figure 15: Method Two, Manually Entering Coordinates 5. Next the offsets, ranges and elevation will have to be set. These parameters are defined below. Center offset: the height the observer is above the ground surface in meters. In the observer point shapefile attribute table it is known as OFFSETA. This simulates the view from a tower, building, or simply a person standing. Terrain offset: must be a positive value, used to simulate tree heights. It is OFFSETB in the observer point shapefile attribute table. Distance Range: this is the radial distance of the line of sight from the center/observer. The range can begin at the observer or a specified distance from it. Default is 0-10km. Azimuth Range: this is the horizontal angle limits of the observer’s field of view, measured in degrees. The default of 0-360 degrees will create a viewshed of a complete circle, any angle less than 360 degrees will create a partial circle. The first azimuth range value is AZIMUTH1 in the observer attribute table while the second is AZIMUTH2. Elevation Range: this is the vertical angle limits of the observer above and below the horizon, default values are -90 to 90 degrees (straight up and down). The first value in the elevation range is VERT1 in the observer attribute table, while the second is VERT2. Observer Elevation: this sets the observer’s elevation to something other than the surface elevation, it is the SPOT attribute in the observer attribute table. Manually enter in the desired values for each of the above mentioned boxes.


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6. For multiple observers, click on the multiple observers box. (see figure 16)

Figure 16: Step 6, Click Multiple Observers Button

7. The multiple observers menu will open. Input all data as per single user then click the add observer button (see figure 17). The observer will be added to the table below. Input data for second observer and click add observer button, continue until all observers have been added.

First observer data

Add observer button

Figure 17: Multiple Observer Options


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Note: If an observer needs to be removed, select it and click on the remove observer button (see figure 18)

Selected observer to be removed

Remove observer button

Figure 18: Removing an observer 8. Once all data/observers have been entered, the apply button will be active, click on it to begin the process. 9. Close off the Radial Line of Sight window. The observer (or observers if multiple ones were used) will be displayed as a red dot and the line of sight will appear as light red bordered polygons (see figure 19)

Figure 19: Observer and radial line of sight


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10. To better view the data, left click on the visibility property in the table of contents and select the properties menu. (see figure 20)

Click on Properties

Right click on the Visibility title

Figure 20: Changing the graphic colours 11. In layer properties, select the symbology tab. Select categories, unique values. Then click on the add all values button. (see figure 21)

Click add all values

Categories, unique values

Select symbology

t b

Figure 21: Visibilty Symbology


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12. Two values will be added to the symbology: 0 for not visible areas and 1 for areas visible to one observer. If multiple observers were used additional values may appear, 2 for areas visible to two observers, 3 for areas visible to three observers… etc. Change colours if desired and hit OK button to apply changes to map data. (see figure 22)

Click OK to apply symbology

changes

0=not visible 1= visible to one observer

Figure 22: All Values of Visibility Displayed 13. The final outcome should look similar to figures 23 and 24.

Figure 23: Outcome for single observer


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Figure 24: Outcome for multiple observers


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Linear and Radial Line of Sight in ArcMap - Dunnett