Sensor Placement and Coverage
If you check Options, Menus tab, Show labs:
- Go to Files, GIS Labs, Sensor coverage
This gives you a DEM and the NLCD
for a location on the Arizona border, in the region where DHS
had a large demonstration project called
P28 which was part of the
Secure Border Initiative (SBInet).
||The diagonal green line is the border which we want to cover with
sensors, represented by a thin shapefile.
The locations of 6 sensors
and their Viewsheds are also shown.
We will calculate the
sensor coverage by
the percentage of the border shapefile that is in the the visible
portion of the viewsheds for the sensors.
You will use sensors with
the following characteristics, set on the
window. The size of the towers matches news reports, but the
characteristics of the sensors (radar, infrared and other according to the news
reports) are hypothetical.
- Range 500-10,000 meter. Sensors cannot operate close to the tower.
- Height 30 m above the
Target height 2 m above the
Horizontal field of view:
60˚. The coverage starts with the
left boundary, and goes to the right boundary. Note that the left and right
boundaries are adjusted to get this width, and the sensors are aimed to the
SW because of the orientation of the border. This could be adjusted.
- Vertical field of view:
20˚. Note that the Max and min
inclination are adjusted, and the aiming point is at -5˚ since the
towers are tall and will be placed on high terrain.
By default, the
program will save the viewsheds in
c:\mapdata\temp, which will be cleaned out
when you close the program. You might want
to change that location, with the Path button on
the bottom of the form, to the directory you are
using for the lab. The program can
regenerate the fans if you save the sensor
locations, but you can can save some time by
saving the viewsheds in a safe location.
New DEM and
load the DEM and NLCD. Locate the international border.
You can note this as an artefact in the DEM, or overlay the state or
county borders on
the map. You can also look at the NLCD, and note the change in coverage at
the border. You probably want a grayscale reflectance
shapefiles, to create an area
shapefile for the international
border. You are creating a small area that covers
the border so that you can determine the effectiveness of sensor placement.
Insure that the shape file plots with a solid fill pattern (Symbol and color selection). Fan coverage
computations will do an intersection of this region with the fan coverage.
map view (best resolution view of
the data, and best chance to get optimal sensor placement)
Go to the
tab on the Options form, and pick Reasonable for "Verify
graphical selection", and
"Graphical blowup" for the Verify option.
Graphical selection might not be very precise, and could place sensors in
holes from which they might not see very much. If you know
coordinates, perhaps from a GPS field survey, you could pick the option to type them in from the keyboard.
fan/viewshed. Place at least 10 sensors to attempt
to cover the border. Insure that you correctly:
Set the parameters given
above for each
sensor in the Viewshed parameters
window. This is especially important for the first
sensor, since the settings will be remembered for the others. Set the
horizontal viewport with the left and right boundaries, and the vertical
viewport with the min and max inclinations, and minimum and maximum ranges.
If you fans are not showing check:
- That the vertical viewport is reasonable. If you place sensors on
tall platforms on hilltops, they might have to be aimed downward.
- That the Opacity of the fans is not set to 0.
Map Overlays Adjust the order of overlays, plotting the Sensor fans
after the Database with the border.
opacity, set with the slider on the Sensor panel; Pick a midrange
opacity for the fans, which will let you see the terrain behind the
After you have entered the sensors,
- Right click on the map and pick "Edit fans",
which brings up a fan edit window
which gives some analysis options.
- Save the sensor locations with Report, DBF on the
fan edit window.
The default location will be cleared when you close the program.
- Restore the sensor locations with File, Load Weapons with
the map window active. This allows the locations and any
changes to be saved between times you run the program.
The key options:
Compute fan coverage
gives the location and characteristics of the sensors, and the coverage
computations of the target shapefile.
- Pick sensors: turns individual sensors on and off.
last revision 4/18/2017