Using the AzEl Mask Tool

STK Pro, STK Premium (Air), STK Premium (Space), or STK Enterprise
You can obtain the necessary licenses for this tutorial by contacting AGI Support at support@agi.com or 1-800-924-7244.

The results of the tutorial may vary depending on the user settings and data enabled (online operations, terrain server, dynamic Earth data, etc.). It is acceptable to have different results.

Capabilities covered

This lesson covers the following STK Capabilities:

  • STK Pro

Problem statement

Engineers and operators need a quick way to determine if structures or vehicles affect visibility between sites, vehicles, or satellites. This gives insight about communications, imaging, radar, and general situational awareness. A ship is deploying a satellite tracking sensor. You need to determine how much of the sensor is blocked by the ship's superstructure.

Solution

Use STK and the AzEl Mask tool to determine if the ship's superstructure interferes with the sensor's access times to the satellite.

What you will learn

Upon completion of this tutorial, you will understand the following:

  • The AzEl Mask tool.
  • The sensor AzEl Mask constraint.
  • How to visualize the sensor AzEl Mask constraint in the 3D Graphics window.

Creating a new scenario

First, you must create a new STK scenario; then build from there.

  1. Launch STK ().
  2. Click Create a Scenario in the Welcome to STK dialog.
  3. Enter the following in the STK: New Scenario Wizard:
    4. Option Value
    Name AzElMaskTool
    Location Default
    Start 24 Jul 2024 16:00:00.000 UTCG
    Stop + 1 day
  4. Click OK to accept your settings.
  5. Click Save () when the scenario loads. A folder with the same name as your scenario is created for you.
  6. Verify the scenario name and location in the Save As dialog.
  7. Click Save.

Save () often during this lesson!

Disabling Terrain Server

Terrain will not be used in your analysis, so you can turn off the Terrain Server.

  1. Right-click on AzElMaskTool () in the Object Browser.
  2. Select Properties () in the shortcut menu.
  3. Select the Basic - Terrain page in the Properties Browser.
  4. Clear the Use terrain server for analysis checkbox.
  5. Click OK to accept the changes and close the Properties Browser.

Inserting a Satellite object

A Satellite object models the properties and behavior of a vehicle in orbit around a central body.

  1. Select Satellite () in the Insert STK Objects tool ().
  2. Select the Orbit Wizard () method.
  3. Click Insert. . ..

Using the Orbit Wizard

The Orbit Wizard is a satellite-level tool designed to assist you in creating any one of several standard orbits, or designing your own satellite orbit.

  1. Enter TestSat in the Satellite Name: field.
  2. Enter 750 km in the Altitude: field of the Definition frame.
  3. Click OK to propagate the satellite and to close the Orbit Wizard.

Inserting a Ship object

A Ship object models the properties and behavior of a ship.

  1. Insert a Ship () object using the Define Properties () method.
  2. Select the Basic - Route page in the Properties Browser.

    Note that the default propagator is GreatArc. The Great Arc Propagator defines the route of a vehicle that follows a point-by-point path along, over, or below the surface of the Earth at a given altitude or depth.

Selecting the altitude reference

Ground vehicles, aircraft, and ships can reference their altitude from mean sea level, terrain data, or WGS84.

  1. Open the Reference: dropdown menu in the Altitude Reference frame.
  2. Select WGS84.

    The WGS84 model uses the coefficients from EGM96 with the shape model of WGS84.

Selecting the route calculation method

STK uses a Route Calculation Method in calculating the route between each waypoint.

  1. Open the Route Calculation Method: dropdown menu.
  2. Select Specify Time.

    The Specify Time method uses the Time properties of each waypoint.

Defining the waypoints

The waypoints that comprise the great arc route are contained in a table that displays each point, along with all of its properties, in sequence.

  1. Click Insert Point.
  2. Set the following parameters:
    LatitudeLongitude
    31.0 deg-70.5 deg
  3. Click Insert Point.

    The Latitude and Longitude will be duplicated for the second waypoint.

  4. Enter 25 Jul 2024 16:00:00.000 UTCG in the Time field for the second waypoint.
  5. Click OK to accept your changes and to close the Properties Browser.
  6. Right-click on Ship1 () in the Object Browser.
  7. Select Rename in the shortcut menu.
  8. Rename Ship1 () to TestShip.

Inserting a Sensor object

A Sensor object models the field of view and other properties of a sensing device attached to another STK object.

  1. Insert a Sensor () object using the Insert Default () method.
  2. Select TestShip () in the Select Object dialog.
  3. Click OK.
  4. Rename Sensor1 () to SatTracker.

Viewing TestShip in the 3D Graphics window

Zooming to TestShip () in the 3D Graphics window will allow you to view changes to SatTracker ().

  1. Bring the 3D Graphics window to the front.
  2. Right-click on TestShip () in the Object Browser.
  3. Select Zoom To in the shortcut menu.

    4. TestShip and attached tracking sensor

    SatTracker () is attached to TestShip's () center point. To model SatTracker () ;correctly, you need to move it to the location on TestShip () where it is actually located.

Positioning the sensor on the model

The location of the sensor is defined using a fixed displacement vector with respect to the parent object’s body frame. The displacement can be defined using either Cartesian or Spherical coordinates, which are in the sensor's parent body frame.

  1. Open SatTracker’s () Properties ().
  2. Select the Basic - Location page in the Properties Browser.
  3. Open the Location Type: dropdown menu.
  4. Select Fixed.
  5. Set the following Fixed Location parameters:
    6. Option Value
    X 25 m
    Y -3.5 m
    Z 21.3 m
  6. Click Apply.
  7. Bring the 3D Graphics window to the front to view the new location of SatTracker ().

    8. New sensor location

    You can also select 3D Model as the Location Type and use the ship model's attach points or the sensor's 3D Graphics Vertex Offset properties to position the sensor.

    When you position the sensor origin, make certain that it is outside the shell of the model; otherwise the AzEl Mask tool will not work.

Using a Complex Conic sensor type

Complex Conic sensor patterns are defined by the inner and outer half angles and minimum and maximum clock angles of the sensor's cone.

  1. Return to SatTracker's () Properties ().
  2. Select the Basic - Definition page.
  3. Open the Sensor Type: dropdown menu.
  4. Select Complex Conic.
  5. Enter 180 deg in the Outer: field of the Half Angles frame.
  6. Click OK to accept your changes and to close the Properties Browser.

Creating an access report from SatTracker to TestSat

Create an access report from SatTracker () to TestSat () without taking the ship's 3D graphics model into consideration.

  1. Right-click on SatTracker () in the Object Browser.
  2. Select Access... () in the shortcut menu.
  3. Select TestSat () in the Associated Objects list when the Access tool opens.
  4. Click .
  5. Click Access. . . in the Reports frame.
  6. Note the Total Duration (approximately 6,789 seconds).
  7. Close the access report and the Access tool.

Creating an AzEl Mask

Use the AzEl Mask tool to create a static body mask file (.bmsk) that can be used in access computations and visualization. Body mask files are used to restrict visibility to a sensor.

Opening the AzEl Mask tool

  1. Maximize your 3D Graphics window.
  2. Select SatTracker () in the Object Browser.
  3. Open the Sensor menu.
  4. Select AzEl Mask....

    The Az/El Mask View window allows you to see the obscuring objects in the six views used in generating the contours. The views will be shown in successive fashion when the Compute. . . button is clicked.

    The AzEl Mask dialog enables you to identify obscuring objects and define the instant in time at which obscuration contours are computed.

Setting up the AzEl Mask tool

Start by setting up the AzEl Mask tool prior to creating a .bmsk file. You will set TestShip () as the obscuring object and the window dimension to 500.

  1. Move the AzEl Mask dialog (AzElMask for SatTracker) to the right so that it isn't on top of the Az/El Mask View window.
  2. Select TestShip () in the Obscuring Objects list.
  3. Enter 500 in the Set the Window Dim: field.
  4. Click Apply.

    5. Larger window sizes produce more accurate masks which require more access computation time. A mask file cannot be generated if the window dimensions are too small or larger than the STK workspace. If the Window Dim: value of 500 places this window outside of your STK workspace, decrease the value until it's inside the STK workspace.

Creating a body mask file

You can now create a static body mask file to use for visualization and analysis.

  1. Click Compute. . ..
  2. Ensure your .bmsk file (use the default file name) will be saved in your scenario folder in the Select Body Mask File dialog.
  3. Click Save.
  4. Close the AzEl Mask dialog and the Az/El Mask View window and when the computation is complete.

Constraining the sensor with the AzEl Mask

You can use the body mask file (.bmsk) as a Sensor object's access constraint.

  1. Open SatTracker's () Properties ().
  2. Select the Basic - Sensor AzEl Mask page.
  3. Open the Use: dropdown menu.
  4. Select MaskFile.
  5. Click the Mask File: ellipsis ().
  6. Browse to your scenario folder if required when the Select File dialog opens.
  7. Select SatTracker.bmsk in the list.
  8. Click Open.
  9. Select Use Mask for Access Constraint.
  10. Click Apply.

Visualizing the sensor AzEl Mask constraint

2D Projection Graphics for sensors control the display of sensor projection graphics in the 2D and 3D Graphics windows. In order to visualize the constraints that the Sensor object is using, you have to define which constraints can be used to modify the field of view of the sensor.

  1. Select the 2D Graphics - Projection page.
  2. Select Use Constraints in the Field of View frame.
  3. Select SensorAzElMask in the list.
  4. Click Apply.

Defining the 3D Graphics Projection properties

3D Graphics Properties for Sensors - Projection is used to control the display of a sensor's cone into space as well as the sensor's extension into space. Extension distances define the length of a sensor's projection. For a constant space projection, enter the projection length in the Space Projection field. In this case, the distance is computed so that the projection of the outermost point on the contour along the bore sight is equal to the distance entered. This is a visualization property, not an analytical property.

  1. Select the 3D Graphics - Projection page.
  2. Enter 30 m in the Space Projection: field in the Extension Distances frame.
  3. Click OK to accept your changes and to close the Properties Browser.

Visualizing the body mask in the 3D Graphics window

You can now view the body mask in the 3D Graphics window.

  1. Bring the 3D Graphics window to the front.
  2. Zoom to TestShip ().
  3. Use your mouse to zoom out until you can the whole ship and some of the body mask.

    4. TestShip body mask

    You can see that SatTracker's () field-of-view is experiencing blockage from TestShip's () superstructure.

Creating a new access report from SatTracker to TestSat

Create a new access report, taking into account the affects of the body mask file.

  1. Right-click on SatTracker () in the Object Browser.
  2. Select Access... () in the shortcut menu.
  3. Select TestSat () in the Associated Objects list when the Access tool opens.
  4. Click Access. . . in the Reports frame.
  5. Note the Total Duration (approximately 5,926 seconds).

    Without taking the ship's superstructure into account, the original total access duration was approximately 6,789 seconds. It is apparent the superstructure reduces the amount of time that you can track the satellite.

  6. Close the access report and the Access tool.

Saving your work

  1. Close any open reports, properties and tools.
  2. Save () your work.

Summary

You modeled a ship deploying a sensor that tracks satellites and performed the following:

  • Used a sensor object to create the field of view.
  • Propagated a single satellite.
  • Generated an access report between the sensor and the satellite to create a benchmark access time.
  • Used the AzEl Mask tool to determine if the ship's superstructure blocked the sensor's field of view.
  • Generated another access report which determined that the superstructure affects your overall access time.