Sensor Pointing File Format (*.sp)

A sensor pointing file is an ASCII text file that is formatted for compatibility with STK and ends in a .sp extension. Sensor pointing files contain attitude data which describes a rotation from the parent body coordinate frame to the sensor body frame. Using sensor pointing files can be useful when you need to import external sensor attitude information into STK to model certain unique circumstances. Sensor pointing is a Basic property of all sensors in STK. The attitude data in any properly formatted Sensor Pointing file can be imported into STK using the External option on the Sensor pointing page of any sensor's Basic properties.

Keywords

Each sensor pointing file, regardless of the type of attitude data in the file, contains some common elements called keywords. Keywords, and their associated values, must precede the specification of the file format and the actual data points.

Keywords used in sensor pointing files are NOT case-sensitive; the capitalization used in this document is for readability.

Keyword	Required	Description
stk.v.<major release number>.<minor release number>	Yes	The version of STK software for which the file is formatted to be used. Files can be created in, and imported to, STK software versions consistent with the file version stamp or higher. The version stamp must be the first line in the Sensor Pointing file. Example: stk.v.6.0 A file created in and stamped with this version could be imported into STK software version 6.0 through the most recent version.
BEGIN Attitude END Attitude	Yes	Sets off the beginning and end of the actual attitude data. All other keyword phrases and data point specification (except the version stamp) will be inside these two keyword phrases. Refer to any of the sample files included in the File Format section for examples.
NumberOfAttitudePoints	Yes	The maximum number of attitude points to read. Example: If you enter: NumberOfAttitudePoints 1000 1000 attitude points would be read.
Sequence	No.	Prior to the `AttitudeTimeAzElAngles` keyword and its data points, you must include a Sequence keyword phrase specifying the order of rotation about the axes. There are only 2 valid sequence values for Azimuth-Elevation angles: 323 and 213. The last rotation is always 0. A 323 sequence (default) is equivalent to using the Rotate About Boresight option for Fixed sensor pointing. A 213 sequence is equivalent to using Hold About Boresight option for Fixed sensor pointing. Default will be supplied. Example: If you enter: Sequence 323 In this case, the sensor will rotate about the boresight. Refer to the help topic on Sensor Orientation Methods for more information on rotation sequence options.
ScenarioEpoch	No	When specified in the file, the reference epoch time for the time values of the attitude data in the file. Specify the value using Gregorian UTC time (`dd mmm yyyy hh:mm:ss.s`). When not specified, the time values of the attitude data in the file are referenced to the STK Scenario Epoch when the file is loaded. A subsequent change to the STK Scenario Epoch will not affect already loaded data. To use the new STK Scenario Epoch as the reference, you must reload the attitude file. The Scenario Epoch keyword and value have no effect on the STK Scenario Epoch, only on the time values of the attitude data in the file. Example: ScenarioEpoch 1 Jan 2003 00:00:00.0 In this case, a time of `5.5` for a particular attitude point would correspond to a time of `1 Jan 2003 00:00:05.5`.
RepeatPattern	No	Attitude data will be used in a cyclical manner. The input data should represent a closed pattern, with the first and last data points being the same.
AttitudeDeviations Rapid	No	Indicates that each time step may have fast and unpredictable pointing changes. It is used to accurately compute Access intervals when constraints depend on sensor pointing. Using the `AttitudeDeviations` keyword may result in decreased performance; therefore, this keyword should only be used when rapid deviations are expected.

File Formats

While the sections above outline the basic format for a Sensor Pointing file, the sections below outline the four formats used to specify actual data points in the Sensor Pointing file.

The first three formats used to specify attitude data for pointing a sensor are identical to those used in the Attitude file format. The links below will redirect you to the help for those formats. The last format, AttitudeTimeAzElAngles, is described below.

Refer to the help topic on Sensor Orientation Methods for more information on specifying attitude data using any of the four formats outlined here.

The following conventions must be observed when specifying data points in any format:

Each line contains only one data point.
The values on each line must be separated by at least one space.
The lines must be listed in ascending order in time but do not have to be evenly spaced in time.
You cannot have multiple points at the same time.
There must be at least as many points as specified by the NumberOfAttitudePoints keyword.
If the attitude is very dynamic (e.g., spinning or slewing rapidly), you should specify more points during the period of rapid motion. For spinning spacecraft you should have at least 3 or 4 points per revolution in order to create an accurate representation of the spinning motion within the Attitude file.

AttitudeTimeAzElAngles Format

The AttitudeTimeAzElAngles keyword phrase is used to indicate that sensor attitude data is provided in time-ordered azimuth and elevation angles. These angles are defined according to the sensor's frame of reference.

Individual data points following the AttitudeTimeAzElAngles keyword look like this:

<TimeInSeconds> <Azimuth> <Elevation>

where,

`<TimeInSeconds>`	The time value of the point in seconds (in the format `xxxx.xxx`) relative to the epoch as defined by the `ScenarioEpoch` keyword.
`<Azimuth>`	The azimuth angle entered in degrees.
`<Elevation>`	The elevation angle in degrees.

Prior to the AttitudeTimeAzElAngles keyword and its data points, you must include a Sequence keyword phrase specifying the order of rotation about the axes.