Several different Orientation Methods are available for specifying the direction in which the sensor or antenna is pointing, with respect to the reference frame. The options available and the data that you must provide depend on the Orientation Method you select. Each method defines orientation of a sensor or antenna with respect to another coordinate frame, which is called a reference frame here. The reference frame is fixed in the sensor's or antenna's parent object (e.g. vehicle or facility). Note that the orientation of the sensor or antenna with respect to other coordinate frames, e.g. central body inertial or central body fixed, will depend on the attitude of its parent object. For example, the default attitude for an Earth orbiting satellite is "Nadir alignment with ECF velocity constraint", which points the satellite's Z axis toward the Earth. Hence, it is reasonable to set the nominal boresight direction of a satellite-based sensor or antenna to be along the Z axis. On the other hand, setting the nominal boresight along the Z axis of a facility is not convenient as it will also be pointed toward the Earth. A better nominal direction in this case will be along the negative Z axis. The reference frame is selected for various STK objects in such a way that using nominal boresight direction along the reference Z axis is reasonable. For a vehicle, the reference frame coincides with the vehicle body frame, which is the frame defined by the vehicle attitude. For a facility, the reference frame is offset from the facility body frame by a 180 deg rotation about the body X-axis.
NOTE: The reference frame mentioned above is introduced only to simplify definitions of sensor and antenna orientation. Reference frames are not actual frames within STK.
The following figures illustrate the form of the four orientation methods. Once you have entered data in a particular method, the other methods' data are automatically updated.
In the four orientation methods made available by STK, nominal sensor or antenna boresight pointing is represented by the following values:
Azimuth = 0 deg
Elevation = 90 deg
About Boresight = Rotate
qx = 0
qy = 0
qz = 0
qs = 1
Euler A = 0 deg
Euler B = 0 deg
Euler C = 0 deg
Sequence = 313
Yaw = 0 deg
Pitch = 0 deg
Roll = 0 deg
Sequence = YPR
The sensor's or antenna's Z axis always coincides with its boresight direction and is unambiguously defined by the azimuth and elevation. However, orientation of the other two axes with respect to the parent's reference frame is determined by the About Boresight option. You can set About Boresight to:
Indicates rotation about the sensor's or antenna's Z axis by the azimuth angle, followed by rotation about the new Y axis by 90 degrees minus the elevation angle. Users familiar with Euler angle sequences will recognize this as a 323 rotation sequence where the first rotation is by the azimuth angle, the second rotation is 90 degrees minus the elevation angle, and the third rotation angle is zero.
When About Boresight is set to Rotate, the complete orientation of the sensor or antenna fixed frame is explained as follows:
The X-axis--also referred to as the "Up vector"--completes the right-handed sensor or antenna frame. It is also evident from the following figures that for the default orientation of elevation = 90 deg and azimuth = 0 deg, the sensor or antenna frame coincides with the parent reference frame:
As illustrated above, attitude definitions for sensors and antennas attached to facilities differ from those used by sensors and antennas attached to vehicles. While boresight azimuth is defined in the facility body frame the same way as it is defined in the vehicle body frame, the elevation (which represents the angle between the XY plane and the boresight as it does in the vehicle body frame) is measured towards the negative Z axis of the facility body frame. This discrepancy impacts the default sensor or antenna elevation angle so that a default elevation angle of 90 deg and azimuth of 0 deg points along the local vertical as the Z axis of the facility body frame points along the nadir. As in the case of a vehicle-based sensor or antenna, the y axis of a facility-based sensor or antenna is located along the intersection of the XY plane and the plane perpendicular to the sensor or antenna boresight, but the angle between the XY plane and the facility's Y axis is azimuth - 180 deg. The X-axis--or "Up vector"--completes the right-handed sensor or antenna frame.
For example, the direction cosine matrix between the sensor or antenna frame and the vehicle body frame with the About Boresight set to Rotate is defined in terms of Az and El as:
Therefore, for a sensor or antenna pointing along the vehicle axes, the corresponding Azimuth and Elevation values are:
| Boresight Direction | Azimuth (deg) | Elevation (deg) |
| +X | 0 | 0 |
| -X | 180 | 0 |
| +Y | 90 | 0 |
| -Y | -90 | 0 |
| +Z | 0 | 90 |
| -Z | 0 | -90 |
The direction cosine matrix between the sensor or antenna frame and the facility body frame with the About Boresight set to Rotate is defined in terms of Az and El as:
Indicates rotation about the Y axis followed by rotation about the new X-axis. This is equivalent to a 213 Euler angle sequence where the third rotation angle is zero. The Hold option produces the same boresight as the Rotate option, which is defined by the azimuth and elevation angles as described above. However, the other two axes, x and y, are obtained via the 213 sequence of Euler rotations with the last Euler angle set to zero. In other words, the Euler rotations are sought first about Y, and then about x such that they produce the z axis along the boresight direction prescribed by the azimuth and elevation.
For example, the direction cosine matrix between the sensor or antenna frame and the vehicle body frame with About Boresight set to Hold is defined in terms of the following two angles:
which can be determined as functions of azimuth and elevation as follows:
For example, the direction cosine matrix between the sensor or antenna frame and the facility body frame with About Boresight set to Hold is defined in terms of the following two angles:
The About Boresight Level option is available only for targeted tracking sensors and is designed to minimize rotation of sensor pattern on the ground. Level indicates boresight is aligned with the line of sight to the target, while the sensor's x-axis is constrained to be in the plane parallel to the meridian plane passing through the target.
The Euler Angles Method uses a 3-rotation sequence about a local axis starting from the parent reference frame and rotating to the sensor or antenna frame where the initial sensor or antenna boresight is along the reference Z-axis as shown in the figure above. The sequence of 3 rotations is defined about either the X, Y or Z axis where X=1, Y=2, Z=3. Hence, a ZXZ sequence is defined as 313.
The overall transformation is a combination of three single-axis rotations about moving axes. Each of these rotations is defined in the following table:
Rotation About X-axis by angle  |
Rotation About Y-axis by angle |
Rotation About Z-axis by angle |
 |
 |
 |
STK provides all possible sequences for combinations of the ijk sequence: 121, 123, 131, 132, 212, 213, 231, 232, 312, 313, 321 and 323.
To determine the direction cosine matrix between the sensor or antenna frame and the reference frame, the transpose of the above equations would be required as:
The Quaternion Method is based on a unit rotation vector and its corresponding angle through which the parent reference frame is rotated in order to align it with the sensor or antenna frame.
The Quaternion is defined as:
where
is the unit rotation vector [e1, e2, e3] expressed in the spacecraft frame about which the spacecraft frame is rotated, and 
is the angle through which the parent reference frame is rotated until it is aligned with the sensor or antenna frame.
Specify the vector and scalar components of the Quaternion describing the rotation from the parent object's reference frame to the sensor or antenna body frame. qx, qy and qz are the vector components and qs is the scalar component. The quaternion must have unit length.