Dimension | Unit | Collections of Current Units |Simple Dimensions List | Compound Dimensions List | Unit Abbreviations List

Units System

Use the units system to specify a different unit of measure for the value of a quantity of a given dimension. Quantities are displayed in text fields and reports, and may be input or output using STK/Connect or the ObjectModel.

Dimension

In STK, dimension means a named group of units for the same measure.

For example, both Distance and SmallDistance are dimensions defined by the software. While many of units available for Distance are also available for SmallDistance, both dimensions have been provided so that you can choose different CurrentUnit settings for each, so that numerical values are appropriately sized.

The software tends to declare a quantity as SmallDistance to represent values that would be typical of vehicle size or smaller, while it declares a quantity as Distance to represent values appropriate for reporting vehicle translational motion. Typically, one uses a larger distance like Kilometers (km) for Distance and a smaller distance like Meters (m) for SmallDistance.

The same unit may appear in different dimensions (e.g., Meters (m), Feet (ft), and several other units are common to Distance and SmallDistance).

Dimensions in STK fall into two categories: simple dimensions and compound dimensions, which are described below.

Dimension Description
Simple Dimension Refers to a dimension where you can select a unit. It does not imply that the dimension is fundamental.

For example, Force is considered a simple dimension because you can choose the units to measure force values; e.g., Newtons (N), Pounds (lbf) etc. Force is not a fundamental unit as it depends on three different fundamental units in the form Mass*Distance/Time^2.

Date is technically not a dimension, but it is treated as one within the software where the units represent different time scales and formats.
Compound Dimension Refers to a dimension built upon a set of simple dimensions. To choose units for the compound dimension, choose a unit from each of its constituents.

For example, Rate is built as Distance/Time whereas SlowRate is built as SmallDistance/Time. Rate allows one to choose its units as Au/sec, but SlowRate does not allow such a choice because it does not allow a choice of Astronomical Units (Au) from SmallDistance.

Unit

In STK, unit means both a specific numerical measure of a value and a specific format of a specific numerical measure of a value.

For example, the Angle dimension contains Degrees (deg) and Radians (rad) as units with numerical measures but also includes the unit Deg:Min:Sec (DMS) which is formatted text breaking out the degree measure of the angle into whole minutes of the angle and seconds of the angle where 1 deg = 60 mins = 3600 secs.

As another example, the Power dimension contains both Watts (W) and dBW (dBW) [i.e., decibel Watts] as units where Watts are a numerical measure and dBW is computed using a log10 function via Power_in_dBW = 10 log10(Power_in_W).

A listing of unit abbreviations, and the dimensions that use them, can be found here.

Collections of Current Units

There are several independent collections of current units in STK. Setting a current unit for a dimension in one collection does not affect the other collections.

  • Scenario
    • The Scenario's current units collection is used by text fields in the GUI to display quantities. See the Scenario->Units page.
    • Use the unit selector () to change the unit of measure for the quantity displayed in the text field.
  • Connect
    • Connect only supports current units for a very limited set of dimensions.
    • See the help page for the connect command Units_Set.
  • Report Manager
    • The Report manager reports data using Report Styles.
    • Quantities in Report Styles can be set to use the current units in collection held by Reporting or can be set to report using a specific unit.
    • To change the units for a report style, click the Units... button on the Report Style window.
    • To change the units in a report, select Report Units () from the report's tool bar.
  • ConnectReport
    • Connect provides a special current units collection to override the units, but not the content type or ordering, in a report style.
    • See the help page for the connect command Units_Set where it discusses ConnectReportUnitsFlag and ConnectReportUnitsFlag.
  • Object Model
    • The object model's current units collection is accessed thru the UnitPreferences property of IAgStkObjectRoot.
    • See the STK Programming help page for IAgUnitPrefsDimCollection.