To transform a star's catalog quantities for a change of epoch and/or equator and equinox.

Namespace: ASCOM.Astrometry.NOVAS
Assembly: ASCOM.Astrometry (in ASCOM.Astrometry.dll) Version: 6.0.0.0 (6.1.1.2619)

Syntax

C#
public short TransformCat(
	TransformationOption3 TransformOption,
	double DateInCat,
	CatEntry3 InCat,
	double DateNewCat,
	string NewCatId,
	ref CatEntry3 NewCat
)
Visual Basic
Public Function TransformCat ( _
	TransformOption As TransformationOption3, _
	DateInCat As Double, _
	InCat As CatEntry3, _
	DateNewCat As Double, _
	NewCatId As String, _
	ByRef NewCat As CatEntry3 _
) As Short
Visual C++
public:
virtual short TransformCat(
	TransformationOption3 TransformOption, 
	double DateInCat, 
	CatEntry3 InCat, 
	double DateNewCat, 
	String^ NewCatId, 
	CatEntry3% NewCat
) sealed

Parameters

TransformOption
Type: ASCOM.Astrometry..::..TransformationOption3
Transformation option
DateInCat
Type: System..::..Double
TT Julian date, or year, of input catalog data.
InCat
Type: ASCOM.Astrometry..::..CatEntry3
An entry from the input catalog, with units as given in the struct definition
DateNewCat
Type: System..::..Double
TT Julian date, or year, of transformed catalog data.
NewCatId
Type: System..::..String
Three-character abbreviated name of the transformed catalog.
NewCat
Type: ASCOM.Astrometry..::..CatEntry3%
The transformed catalog entry, with units as given in the struct definition

Return Value

 = 0 ... Everything OK.
 = 1 ... Invalid value of an input date for option 2 or 3 (see Note 1 below).
 = 2 ... Catalogue ID exceeds three characters
 

Remarks

Also used to rotate catalog quantities on the dynamical equator and equinox of J2000.0 to the ICRS or vice versa.

1. 'DateInCat' and 'DateNewCat' may be specified either as a Julian date (e.g., 2433282.5) or a Julian year and fraction (e.g., 1950.0). Values less than 10000 are assumed to be years. For 'TransformOption' = 2 or 'TransformOption' = 3, either 'DateInCat' or 'DateNewCat' must be 2451545.0 or 2000.0 (J2000.0). For 'TransformOption' = 4 and 'TransformOption' = 5, 'DateInCat' and 'DateNewCat' are ignored.

2. 'TransformOption' = 1 updates the star's data to account for the star's space motion between the first and second dates, within a fixed reference frame. 'TransformOption' = 2 applies a rotation of the reference frame corresponding to precession between the first and second dates, but leaves the star fixed in space. 'TransformOption' = 3 provides both transformations. 'TransformOption' = 4 and 'TransformOption' = 5 provide a a fixed rotation about very small angles (<0.1 arcsecond) to take data from the dynamical system of J2000.0 to the ICRS ('TransformOption' = 4) or vice versa ('TransformOption' = 5).

3. For 'TransformOption' = 1, input data can be in any fixed reference system. for 'TransformOption' = 2 or 'TransformOption' = 3, this function assumes the input data is in the dynamical system and produces output in the dynamical system. for 'TransformOption' = 4, the input data must be on the dynamical equator and equinox of J2000.0. for 'TransformOption' = 5, the input data must be in the ICRS.

4. This function cannot be properly used to bring data from old star catalogs into the modern system, because old catalogs were compiled using a set of constants that are incompatible with modern values. In particular, it should not be used for catalogs whose positions and proper motions were derived by assuming a precession constant significantly different from the value implicit in function 'precession'.

See Also