Vector File Format (*.vd)

This is the version of STK software associated with the file formatting. You can create files in this format and import them into any STK software version at this level or higher.

The version stamp must be the first line in the file.

Example:

stk.v.11.0

You can set this value to determine the level of message(s) you receive from STK as it attempts to read the file. The value options are:

• Errors - You only receive the reported error messages.
• Warnings - You receive error messages plus reporting on other information (e.g., unrecognized keywords).
• Verbose - You receive all that is in Warnings plus a success message if STK reads and accepts the complete file.

AGI recommends using this. When specified, it indicates the maximum number of vector data points to read from the file. When not specified, all vector data points in the file will be used.

Prior to STK 11.5, this keyword was required.

Example:

NumberOfVectorDataPoints 6

then STK would read up to six vector data points.

The default is the actual scenario epoch in the STK scenario.

• Lagrange (Default)
• Hermite - This option takes advantage of velocity information, if available, in order to achieve smoother vector interpolation. It is especially useful when using tables containing very irregularly spaced data points or data that can be susceptible to ringing and aliasing effects if derivative information is not considered during interpolation. Hermitian interpolation assumes that the rate component of the vector is its derivative. Do not use Hermitian interpolation when rate data is not available as part of the vector table.

Default is Lagrange.

Example:

InterpolationMethod Hermite

The value is one less than the number of points used in the interpolation. For the Lagrange interpolation method, this is also the interpolation order. For the Hermitian interpolation method, the interpolation order is:
(2 x InterpolationSamplesM1) + 1.

The default value is 5.

Example:

InterpolationSamplesM1 5

The default is the central body for the vehicle, and Earth is the default for the vehicle.

Example:

CentralBody Earth

The manner in which Cartesian velocity is computed from the Cartesian position generated from the position data in the file if rate information is not provided directly by the file. The default value is DerivativeOfInterpolatingPolynominal. Other values are: 

• ForwardDifference

• BackwardDifference

• CentralDifference

AGI recommends specifying these, which are the reference axes in which the vector data components are expressed.

You can use any of the pre-defined reference axes. For a complete list of VGT central body frames, go to the Vector Geometry tool in STK's Analysis Workbench capability and select a specific primary or secondary body, or an object on a particular central body. All supported VGT components, including reference frames, will appear for your selection.

You can also define a new set of axes using the Vector Geometry Tool (VGT). You can then specify the name of your new axes and the name of the STK object to which it corresponds. VGT-created axes must use the keyword CoordinateAxes AWB. For example, CoordinateAxes AWB NorthEastDown Aircraft/AircraftName.

CoordinateAxes AWB replaces CoordinateAxes Custom as the required keyword for VGT-created axes. STK still supports the CoordinateAxes Custom keyword, for backward compatibility.

The default is Inertial, which is ICRF for the Earth and Sun.

Examples:

CoordinateAxes TrueOfEpoch
CoordinateAxes AWB TopoCentric Facility/MyLaunchSite TopoCentric

The name of the STK object is optional if the object that is importing the vector data is the object on which axes are defined.

Specify the epoch time for the coordinate axes in Gregorian UTC time (dd mmm yyyy hh:mm:ss.s).

These are required with coordinate axes that reference an epoch:

• MeanOfEpoch
• TrueOfEpoch
• TEMEOfEpoch
• AlignmentAtEpoch

Example:

CoordinateAxesEpoch 1 Jun 2003 12:00:00.0

Specify the unit of the tabulated data in the file. The unit must be valid for the specified DimensionName.

Use this only if you provide a DimensionName.

You can only specify a unit that is valid for tabulated data with numeric values.

Example:

For DimensionName Angle:

• Invalid DimensionUnit: Deg:Min:Sec
• Valid DimensionUnits: Degrees, Radians, Arc Minutes, etc.

The TimeFormat keyword is the time format abbreviation, such as EpSec for Epoch Seconds or JDate for Julian Date. For time format abbreviations, see DateTime Formats.

This defines the date format of time tags. If set, each line of data in the file begins with a time in this date format followed by the rest of the data.

Spaces are valid whenever the format admits them (e.g., 1 Jan 2007 12:00:00.000).

Quotes around time strings are invalid.

Examples:

TimeFormat DD/MM/YYYY

TimeFormat GPSZ

These keywords mark the beginning and end of the TrendingControl section. STK will sample the data in this section when determining trends for event detection. For example, a drastic change in motion may indicate an event (especially if the change is brief).

The TrendingControl section can include either the TrendingControlTimes subsection or the TrendingControlStep.

Keyword History

The TrendingControl keywords were introduced in STK 11.6.0.

You can include TrendingControlTimes section in the file if the TrendingControlStep keyword is not used.

This section contains a list of times (one per line) that should be sampled for determining trends for event detection.

If a TimeFormat keyword precedes this section, then this section must adhere to the format. Otherwise, the times are in seconds since the ScenarioEpoch specified in the file.

Keyword History

The TrendingControlTimes keywords were introduced in STK 11.6.0.

You can include the TrendingControlStep keyword in the file if the TrendingControlTimes section is not used.

The keyword specifies the step size, in seconds, that STK will use when sampling times in the file. STK will select samples as far apart as possible without exceeding the step size. Controlling the step size is most useful when the sample times in a file are dense. STK will sample at a lower density than the file's data, but the points will still be close enough to detect drastic changes in motion.

Keyword History

The TrendingControlStep keyword was introduced in STK 11.6.0.