Report Units of Measure
You can change units of measure for a report style or a displayed report.
To change or view the units for selected content in a report style, select Content in the Report Properties browser, choose a particular section, line, or data provider under Report Contents, and click Units....
To change or view the units for a displayed report, right-click the report and select Report Units.... To display all unit dimensions in the Units window, select Show All Dimensions.
You can change all applicable units of measure for the data selected. Choose one of the following to set the units for the report:
- Use default units of measure. Select Use Defaults.
- Change the Units of Measure. Clear Use Defaults and select a new unit value.
- Set new default units of measure. Select a new unit value for one or more selected dimensions and select Set as Default. The units of measure set here are used as the default units for all data displayed. Changes made in the Units window do NOT affect the units set at the scenario level nor do they permanently change the units for the report style.
For more information, see Time Standards and Comments on Selected Units of Measure.
Time Standards
International Atomic Time (TAI) is a physical time scale affected by the Earth's gravitational and rotational potential, and deduced from a weighted average of various international frequency standards. Relative weighting is based on the historical stability of the individual standards. TAI is maintained by the Bureau International des Poids et Mesures (BIPM) and is the basis of other time scales.
Global Positioning System Time (GPS) is the background (reference) time scale of that satellite-based navigation system; ideally, it is steered to lag TAI by nineteen (19) seconds, so GPS Time = TAI - 19 seconds.
Universal Time (UT1) is the angular measure of Earth rotation inferred from observations. Earth-rotation angle provides a sequentially increasing continuum that is everlasting and widely apparent, and serves as the astronomical basis of civil time of day. The angular rate of modern-day UT1 has been defined to closely follow Newcomb's convention for mean solar time, based on the mean motion of the Sun deduced from 19th-century observations.
Coordinated Universal Time (UTC) is a broadcast time standard providing both astronomical time of day and atomic-time interval. UTC is kept within +/-0.9 s of UT1 by the introduction of leap seconds and is therefore a legally recognized proxy for Universal Time in most countries. UTC is always offset from TAI by an integer number of seconds and is thus a carrier of precision frequency and time interval for broadcast standards based on the SI second.
Zulu time is synonymous with UTC.
Greenwich Mean Time (GMT), generally a synonym for Universal Time and UTC, is used in STK as a synonym for Coordinated Universal Time (UTC).
Local Time is civil time maintained with an offset considering the observer's longitude as defined by the computer hosting STK. In STK, local time is a synonym for Zone Time, which generally maintains hourly offsets from UTC, and is realized based on the computer system clock configuration.
The local time offset from UTC changes between local Standard Time (LST) and local Daylight or Summer Time (LDT) as determined by the computer hosting STK. In the United States through 2006, local time changed from Standard Time to Daylight Time at 02:00 LST to 03:00 LDT on the first Sunday in April, and returned at 02:00 LDT to 01:00 LST on the last Sunday in October. Effective 2007, local time changed from standard time to daylight time at 02:00 LST to 03:00 LDT on the second Sunday in March and returns at 02:00 LDT to 01:00 LST on the first Sunday in November. Some areas of the US do not recognize daylight or summer time.
STK determines local time and handles daylight time as follows:
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In Microsoft Windows, local time conversions to UTC time now use the time zone rules stored as part of the Windows operating system, in its registry. When STK is computing a local time, it applies the Windows time zone rules to determine the local-to-UTC conversion, including the offset for Daylight Saving Time in effect at that time.
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For Linux, STK does not determine if daylight savings time should be applied based on the epoch requested. Instead, it will use the computer's UTC offset (including the Daylight Savings Time offset) when STK was started and apply that constant offset between local and UTC to all date calculations for all times. If your scenario is outside your current local time, where the local-to-UTC offset is different during the scenario times than the offset determined at STK startup, the local time might be off for some or all of your calculations.
Terrestrial Time (TT) is a theoretically ideal time at the Earth geoid. A practical realization is TT = TAI + 32.184 seconds. The quantity ΔT, where ΔT = TT - UT1, is the difference between this ideal time scale and the rotation of the Earth. TT is also known as Terrestrial Dynamical Time (TDT) when considered as a coordinate time for geocentric orbits. TT is the successor of pre-relativistic Ephemeris Time (ET).
Barycentric Dynamical Time (TDB) is intended to serve as the independent argument of barycentric ephemerides and equations of motion. It is defined as being linearly related to Barycentric Coordinate Time (TCB), where TCB is further related to TT through a complex sequence of relativistic transformations. The linear relationship between TDB and TCB is chosen such that the rate of TDB closely matches TT for the time span covered by the JPL Development Ephemerides. TDB is sometimes designated as Barycentric Ephemeris Time (Teph) when used as the time scale of the JPL ephemerides.
Comments on Selected Units of Measure
| Dimension | Unit | Comment |
|---|---|---|
| DateFormat | EpSec, EpMin, EpHr, EpDay, EpYr |
Epoch Seconds, Epoch Minutes, Epoch Hours, Epoch Days, and Epoch Years Epoch is calculated as time elapsed relative to the scenario epoch. |
| LCLG, UTCG |
Gregorian Local / UTC This is the Local / Coordinated Universal Time date and time displayed in Gregorian format, for example 1 Jul 2007 12:00:00.000. |
|
| LCLJ, UTCJ |
Julian Local / UTC This is Local / UTC date and time displayed in day of year format (182/07 12:00:00.000). The leading two digits of the year are assumed to be 19 for YY values of 60-99 or greater and 20 for YY values of 00-59. |
|
| LTZG |
Local Time Zone Gregorian If no offset is provided, then this is interpreted as a local time. On a GUI, it would be converted into the form with the correct offset for that time zone. If you provide an offset (+ or - hh:mm), STK applies it as a constant offset from UTC for the whole scenario. You do not have to use an offset matching the current time zone, but STK still displays time in current local time zone representation. An example with the offset included is 25 Jan 2021 12:01:00.000-05:00. |
|
| UTCJFOUR |
Julian4 UTC This is UTC date and time displayed in day-of-year format, with four digits representing the year (182/2007 12:00:00.000). |
|
| JDate |
Julian Date JDate equals 2451544.5 plus the number of elapsed UTC days since the epoch of AD January 1, 2000, at 0 hours of the Gregorian calendar (2454283.000000). The addition of 2451544.5 correlates the zero epoch at noon of November 24, 4713 BC. UTC date conversions with this format may not appear accurate before 1972 because UTC days were not defined using leap seconds. Also, time during a leap second may display incorrectly due to an incorrect assumption regarding the length of UTC day when using this format. |
|
| JDateOff |
Julian Date Offset This is computed as the Julian Date minus the user-specified offset. Modified Julian Dates can be represented by specifying an offset of 2,400,000.5. |
|
| MisElap |
Mission Elapsed Time This is the time elapsed relative to a user-specified epoch. Enter the epoch in text field. The elapsed time is presented in terms of days, hours, minutes, and seconds (100/12:30:05.00). If you use this option, it is best to enter the dates in the Time Period and Animation pages before changing the DateFormat to Mission Elapsed. This is because Mission Elapsed Time is measured relative to the existing scenario epoch. |
|
| GMT |
Greenwich Mean Time The same as UTC date and time, displayed as the day of year, integer seconds into the day and the year (182/43200 2007). This format has limited precision and a confusing nomenclature, and is therefore not recommended for general use. |
|
| ModJDate |
Modified Julian Date This is the UTC date and time defined by a fixed offset from the Julian date. Sets the beginning of days at 0 hours instead of 12 hours, and it reduces the number of digits in day numbering. The modified Julian date is obtained by subtracting 2,400,000.5 from the Julian date. |
|
| JED |
Julian Ephemeris Date This is a measure of elapsed TDT days, starting from noon on November 24, 4713 BC, of the Gregorian calendar, in the TT time scale. TT (formerly ET) coincides with UT around AD 1902 and was ahead of UT by ~64s in AD 2000. A TT day is 86400 SI seconds in duration. |
|
| TDTG |
Gregorian TDT This is Terrestrial Time (formerly known as Terrestrial Dynamical Time) displayed in Gregorian calendar format. |
|
| TDBG |
Gregorian TDB This is a Barycentric Dynamical Time displayed in Gregorian format. |
|
| TAIG |
Gregorian TAI This is International Atomic Time displayed in a Gregorian calendar format. |
|
| TAIJ |
Julian TAI This is International Atomic Time displayed in a Julian day-of-year format. |
|
| GPSG |
Gregorian GPS This is GPS time displayed in Gregorian calendar format. |
|
| GPS |
GPS time GPS time is natively expressed as elapsed time since the GPS epoch of 6 January 1980 00:00:00:00 UTC. The elapsed time is presented in terms of weeks and seconds into the week (1434:43214.000). |
|
| GPSZ |
GPS Z count This is GPS time expressed as elapsed time since the GPS epoch of 6 January 1980 00:00:00:00 UTC. The elapsed time is presented in terms of Z counts (1.5 second increments) (578217609.333). This differs from normal GPS convention, where the Z count is represented as the number of whole weeks since the GPS epochs and the number of 1.5 second increments into the week. |
|
| EarthEpTU |
Earth canonical time This is the time elapsed since the scenario epoch measured in Earth canonical time units, where one time unit equals |
|
| SunEpTu |
Sun canonical time This is the time elapsed since the scenario epoch measured in Sun canonical time units, where one time unit equals |
|
| DD/MM/YYYY |
This is UTC date and time displayed with the indicated format using hours, minutes, and seconds to represent the time of day (01/07/2007 12:00:00.000). |
|
| YYDDD |
This is UTC date displayed in SGP4 Epoch date format using the last two digits of the current year, the whole day of the year, and the fractional day of the year (07182.50000000). The leading two digits of the year are assumed to be 19 for YY values of 60-99 or greater and 20 for YY values of 00-59. |
|
| YYYY/MM/DD |
This is UTC date and time displayed with the indicated format using hours, minutes, and seconds to represent the time of day (2007/07/01 12:00:00.000). |
|
| YYYY:MM:DD |
This is UTC date and time displayed with the indicated format using hours, minutes, and seconds to represent the time of day (2007:07:01:12:00:00.000). |
|
| YYYYDDD |
This is UTC date displayed using the year, the whole day of the year, and the fractional day of the year (2007182.50000000). |
|
| YYYYMMDD |
This is UTC date and time displayed with the indicated format and the fractional day of the month (20070701. 50000000). |
|
| ISO-YD | This is UTC date and time formatted as YYYY-DDDThh:mm:ss.sss, where YYYY is the 4 digit year, DDD is the three-digit day of the year, hh is the two-digit hour, mm is the two-digit minute, and ss.sss is a floating point representation of seconds into the minute, where the precision is specified via the time precision setting. | |
| ISO-YMD | This is UTC date and time formatted as YYYY-MM-DDThh:mm:ss.sss, where YYYY is the four-digit year, MM is the two-digit month, DD is the two-digit day of the month, hh is the two-digit hour, mm is the two-digit minute, and ss.sss is a floating point representation of seconds into the minute, where the precision is specified via the time precision setting. | |
| ISO-LTZ |
ISO Local Time Zone This is LTZG date and time formatted as YYYY-MM-DDThh:mm:ss.sss+hh:mm, where YYYY is the four-digit year, MM is the two-digit month, DD is the two-digit day of the month, hh is the two-digit hour, mm is the two-digit minute, and ss.sss is a floating point representation of seconds into the minute, where the precision is specified via the time precision setting. The end +hh:mm captures the optional offset input, where "+" really means "+ or -". An example with the offset included is 2021-01-25T12:00:00.000-05:00. |
|
| Mass | Pounds | One pound mass is the quantity of matter that would weigh one pound at sea level. |
| SmallDistance | All | This dimension supplies units that are used to describe the smallest STK distances. |
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