Keywords | {MethodOption} | Data Column Formats
Great Arc Propagator File Format (*.pg or *.ga)
A great arc propagator file, also known as a waypoint file, is an ASCII text file that is formatted for compatibility with STK and ends in a .pg or .ga extension. Great arc propagator files define the path of an aircraft, ship, or ground vehicle. You can use a great arc propagator file to provide STK with route data that models certain unique circumstances for a vehicle. The great arc propagator file consists of a list of waypoints, which STK will connect with great arc paths.
Keywords
A great arc propagator file contains some common elements called keywords. In order for a great arc file to be formatted properly, it must contain the following keywords. (Keywords and their associated values must precede the specification of the actual data points.) See sample file.
Keywords used in great arc files are not case-sensitive; the capitalization used in this file is for readability.
| Keyword | Required | Description |
|---|---|---|
| stk.v.<major release number>.0 | Yes | The version of STK software for which the file is formatted. Files can be created in, and imported to, STK software versions either consistent with the file version stamp or a later version.
Example: stk.v.4.0You can import a file created in and stamped with version 4.0 into STK software version 4.0 or later. |
| BEGIN GreatArc END GreatArc |
Yes | Sets off the beginning and end of the great arc route definition. Refer to any of the {MethodOption} sample files below for more examples. |
| Method | Yes |
Specifies the method used to compute the great arc path. If you specify the Method keyword, you must also specify the Method DetVelFromTimeMethod DetVelFromTime creates a route where the time of waypoint arrival is specified and the rate information is computed. Refer to any of the |
| TimeOfFirstWaypoint | Yes | Specifies the start time for the vehicle route in Gregorian UTC time (dd mmm yyyy hh:mm:ss.sss, for example: 1 Nov 2004 12:00:00.000). This entry must precede the waypoint entries. Refer to any of the {MethodOption} sample files below for examples. |
| ArcGranularity | Yes |
Specifies the maximum angle between successive ephemeris points. Example:ArcGranularity 0.01745Specifying an ArcGranularity of 0.01745 radians generates ephemeris points with separation angles of no more than 1 degree. |
| AltRef | Yes |
Specifies that altitude can be referenced to one of the following:
AltRef WGS84AltRef WGS84 indicates that the altitude will reference the central body's reference ellipsoid. |
| NumberOfWaypoints | Yes |
Specifies the number of waypoints. This entry must precede the specification for the waypoints. Example:NumberOfWaypoints 5NumberOfWaypoints 5 indicates that the data for five waypoints are specified inside the BEGIN Waypoints and END Waypoints keyword block. |
| BEGIN Waypoints END Waypoints |
Yes | Sets off the beginning and end of the waypoints. |
{MethodOption}
You can use three {MethodOption}s in conjunction with the Method keyword to indicate the method to be used to calculate the great arc route.
| {MethodOption} | Description |
|---|---|
| DetVelFromTime |
Specifies a trajectory where the time of waypoint arrival is specified and the rate information is computed. Acceleration is assumed to be zero. The acceleration data column is a required placeholder for this method. The rate data column is also a required placeholder for this method. The rate value is recalculated by STK. Refer to a sample file of a great arc file using the DetVelFromTime {MethodOption}. |
| DetTimeFromVelAcc |
Specifies a trajectory where the waypoints must contain accurate rate and acceleration information; the time information is then computed during the ephemeris generation. The time column is a required placeholder for this method. Time values are recalculated by STK. Refer to a sample file of a great arc file using the DetTimeFromVelAcc {MethodOption}. |
DetTimeAccFromVel (Default) |
Specifies a trajectory where the rate information is specified and the time and acceleration information are computed to ensure a smooth rate across waypoints. Both time and acceleration data columns are required placeholders for this {MethodOption}. Time and Acceleration values are recalculated by STK. Refer to a sample file of a great arc file using the DetTimeAccFromVel {MethodOption}. |
Data Column Formats
Each line of a Great Arc file requires data columns 1 through 6 and these columns must be in the order that they are listed in the table below. Each of the six required columns must have a value. Depending on the {MethodOption}, not all columns represent required input data. These columns are referred to as placeholders and the values for the placeholders are recalculated by STK based on the {MethodOption} used.
The turn radius can be added as the seventh column to any of the three {MethodOption}s.
The following table does not include STK internal data that is saved with an STK-generated waypoint.
| Column | Data Format | Description |
|---|---|---|
| 1 | ttttt.ttt | Time of waypoint in epoch seconds. This column is a required placeholder for both the DetTimeFromVelAcc and DetTimeAccFromVel {MethodOption}s. |
| 2 | lat | Latitude of waypoint in degrees. |
| 3 | lon | Longitude of waypoint in degrees. |
| 4 | alt | Altitude of waypoint in meters |
| 5 | rate | Velocity from this waypoint to the next in meters per second. This column is a required placeholder for the DetVelFromTime {MethodOption}. |
| 6 | accel | Acceleration from this waypoint to the next in meters per second2. This column is a required placeholder for both the DetVelFromTime and DetTimeAccFromVel {MethodOption}s. |
| 7 | turn radius | Curvature of the arc between this waypoint and the next in meters. Optional. |
Data units in great arc files are STK default units and cannot be changed. You must enter altitude in meters, time in seconds, and angles in degrees. Each number is converted inside the application to the user-specified scenario units.
For example, if you enter an altitude of 10000.00 (10000 meters) in your external great arc file, and the scenario distance unit is kilometers (km), you will see 10 km in the Altitude option on the Route page when you load the great arc file.