Sensor Azimuth-Elevation Mask

To apply an azimuth-elevation mask to a sensor, go to the Basic > Sensor AzEl Mask page of a sensor's Properties window and select the MaskFile option under Use. For Mask File, click the ellipsis and select an azimuth-elevation mask file (.aem) or a body mask file(*.bmsk).

An azimuth-elevation mask file identifies areas of exclusion, and a body mask file identifies areas of inclusion and exclusion for the relative position vector from the sensor to a target of interest, expressed using azimuth and elevation angles. These angles are measured by specifying a pole axis and reference axis in the frame of some reference axes. When the mask file itself does not specify the reference axes, STK assumes the axes are the sensor parent's body axes. The azimuth angle is measured in the plane perpendicular to the pole axis from a reference axis in that plane to the projection of the relative position vector into the plane. The elevation angle is measured from the plane to the relative position vector.

When using a body mask file, the pole axis is the +Z axis and the reference axis is the +X axis. Azimuth is measured positively using the right-hand rule about the +Z axis, and elevation is measured positively toward the +Z axis from the X-Y plane.

When using an azimuth-elevation mask file, the pole axis is set by the Primary Boresight Axis. If you specify the pole axis as the X or Y axis, the elevation is measured positively toward the +X or +Y axis, and the azimuth is measured from the +Y axis or +Z axis, respectively, where the azimuth is positive using the right-hand rule for the pole axis. If you specify the pole axis as the Z axis, then the reference axis is the +X axis, and azimuth is measured positively using the right-hand rule about the +Z axis, but special rules apply for measuring elevation:

• If either the mask file specifies the reference axes or the sensor's parent is a vehicle (i.e., Aircraft, GroundVehicle, LaunchVehicle, Missile, Satellite, Ship), then elevation is measured positively toward the +Z axis.
• For all other cases, the elevation is measured positively toward the -Z axis. This applies to a facility, place, or target.

In the body axes of a Facility/Place/Target, the +X axis points toward local north while the +Z axis points downward into the ground (along detic nadir). Thus, the measuring of elevation as positive toward the -Z axis (i.e., toward detic zenith) in this case is in keeping with common conventions.

If you enter negative values for boresight elevation in an AEM file, you should bear in mind the following: The Az/El mask defines an area of exclusion, where the exclusion region contains elevations smaller than the elevation values specified in the mask. Thus, if you define an elevation value of -85 deg for a sensor on a satellite with the intent of defining a 5-degree inclusion region along the -Z axis, the result, instead, will be a 5-degree exclusion region in that direction.

Use Mask for Access Constraint option

Select the "Use Mask for Access Constraint" check box to make available the Sensor Az-El Mask constraint on the Constraints->Basic properties page. You can use this option only if you apply a mask file to the sensor.