If a "Sky Co-ordinate System" specification is supplied (using parameter FRAMEIN) for a celestial co-ordinate system, then an epoch value is needed to qualify it. This is the epoch at which the supplied sky positions were determined. It should be given as a decimal years value, with or without decimal places ("1996.8" for example). Such values are interpreted as a Besselian epoch if less than 1984.0 and as a Julian epoch otherwise. [Dynamic]

If a "Sky Co-ordinate System" specification is supplied (using parameter FRAMEOUT) for a celestial co-ordinate system, then an epoch value is needed to qualify it. This is the epoch at which the supplied sky positions were determined. It should be given as a decimal years value, with or without decimal places ("1996.8" for example). Such values are interpreted as a Besselian epoch if less than 1984.0 and as a Julian epoch otherwise. [Dynamic]

These parameters supply the values of "sub-expressions" used in the expressions XFOR and YFOR. These parameters should be used when repeated expressions are present in complex transformations. Sub-expressions may contain references to other sub-expressions and constants (PA-PZ). An example of using sub-expressions is:

If TRTYPE="STRUCT" is chosen then this parameter’s value controls whether the forward or inverse mapping in the transform structure is used. [TRUE]

If TRTYPE="WCS" then the transformation is a mapping from the frame specified by this parameter to that specified by the FRAMEOUT parameter. The value of this parameter can be one of the following:

• A domain name such as SKY, AXIS, PIXEL, etc.
• An integer value giving the index of the required Frame within the WCS component.
• A "Sky Co-ordinate System" (SCS) value such as EQUAT(J2000) (see section "Sky Co-ordinate Systems" in SUN/95).

A domain name is usually the most suitable choice. [PIXEL]

If TRTYPE="WCS" then the transformation is a mapping from the frame specified by the FRAMEIN parameter to that specified by this parameter. The value of this parameter can be one of the following:

• A domain name such as SKY, AXIS, PIXEL, etc.
• An integer value giving the index of the required Frame within the WCS component.
• A "Sky Co-ordinate System" (SCS) value such as EQUAT(J2000) (see section "Sky Co-ordinate Systems" in SUN/95).
• Null (!), indicating the Current frame.

[!]

If NDFNAMES is TRUE and the transformation is to be specified using a WCS component (TRTYPE="WCS"), then this parameter controls whether or not the WCS component should be located in each of the NDFs. If set FALSE, the WCSFILE parameter will be used.

If NDFNAMES is TRUE and the transformation is to be specified using a TRANSFORM structure (TRTYPE="STRUCT") then this parameter controls whether or not the structure should be located in the CCDPACK extension of each of the images. If set FALSE, the TRANSFORM parameter will be used.

If this option is chosen then the WCS component or transform structure in EACH image will be applied to the associated position list. So for instance if you have a set of registered images and positions these may be transformed all at once to and from the reference coordinate system. [TRUE]

This parameter is used to access the names of the lists which contain the positions and, if NDFNAMES is TRUE, the names of the associated images. If NDFNAMES is TRUE the names of the position lists are assumed to be stored in the extension of the images (in the CCDPACK extension item CURRENT_LIST) and the names of the images themselves should be given in response (and may include wildcards).

If NDFNAMES is FALSE then the actual names of the position lists should be given. These may not use wildcards but may be specified using indirection (other CCDPACK position list processing routines will write the names of their results files into a file suitable for use in this manner) the indirection character is "$$^".

Name of the CCDPACK logfile. If a null (!) value is given for this parameter then no logfile will be written, regardless of the value of the LOGTO parameter.

If the logging system has been initialised using CCDSETUP then the value specified there will be used. Otherwise, the default is "CCDPACK.LOG". [CCDPACK.LOG]

Every CCDPACK application has the ability to log its output for future reference as well as for display on the terminal. This parameter controls this process, and may be set to any unique abbreviation of the following:

• TERMINAL – Send output to the terminal only

• LOGFILE – Send output to the logfile only (see the LOGFILE parameter)

• BOTH – Send output to both the terminal and the logfile

• NEITHER – Produce no output at all

If the logging system has been initialised using CCDSETUP then the value specified there will be used. Otherwise, the default is "BOTH". [BOTH]

Only used if NDFNAMES is FALSE. This specifies the name of a file to contain a listing of the names of the output lists. This file may then be used to pass the names onto another CCDPACK application using indirection. [TRANLIST.LIS]

If TRUE then the routine will assume that the names of the position lists are stored in the NDF CCDPACK extensions under the item "CURRENT_LIST". The names will be present in the extension if the positions were located using a CCDPACK application (such as FINDOBJ). Using this facility allows the transparent propagation of position lists through processing chains.

If a global value for this parameter has been set using CCDSETUP then that value will be used. [TRUE]

A list of names specifying the result files. The names of the lists may use modifications of the input names (image names if available otherwise the names of the position lists). So if you want to call the output lists the same name as the input images except to add a type use:

If no image names are given (NDFNAMES is FALSE) then if you want to change the extension of the files (from ".CENT" to ".TRAN" in this case) use:

Or alternatively you can use an explicit list of names. These may use indirection elements as well as names separated by commas.

These parameters supply the values of constants used in the expressions XFOR and YFOR. Using parameters allows the substitution of repeated constants (with extended precisions?) using one reference. It allows easy modification of parameterised expressions (expressions say with an adjustable centre) provided the application has not been used to apply a new transform using expressions. The parameter PI has a default value of 3.14159265359D0. An example of using parameters is:

This maps (X,Y) to (R,THETA) about a specified centre.

The form of the transformation which is to be applied to the positions in the input lists. This can take the values

• COEFF

• EXPRES

• WCS

• STRUCT

or unique abbreviations of.

COEFF means that a linear transformation of the form:

is to be applied to the data. In this case a prompt for the values of the coefficients A-F is made.

EXPRES indicates that you want to supply algebraic-like expressions to transform the data. In this case the parameters XFOR and YFOR are used to obtain the expressions. Things like:

are allowed. The expression functions must be in terms of X and Y. For a full set of possible functions see SUN/61 (TRANSFORM).

WCS means that the transformation will be taken from the WCS component of an image. In this case the name of the image containing the WCS component should be supplied (this will be picked up automatically through the association of an image and a position list if NDFNAMES and INEXT are both TRUE). The transformation will be that between the frames defined by the FRAMEIN and FRAMEOUT parameters.

STRUCT signifies that a transform structure (probably created by REGISTER or CCDEDIT) is to be applied to the data. In this case the name of the object containing the structure should be supplied (this will be picked up automatically through the association of an image and a position list if NDFNAMES and INEXT are both TRUE) and whether to use the forward or inverse mappings (the FORWARD parameter). [COEFF]

If TRTYPE="COEFF" is chosen then the values of this parameter are the 6 coefficients of a linear transformation of the type:

The default is the identity transformation. [0,1,0,0,0,1] [PA,PB,PC,PD,PE,PF]

If TYPE="STRUCT" and INEXT=FALSE then this parameter is used to access the HDS object which contains the transform structure. The standard place to store a transform structure (in CCDPACK) is

• NDF_NAME.MORE.CCDPACK.TRANSFORM

Only one structure can be used at a time.

If TRTYPE="WCS" and INEXT is false, then this parameter gives the name of the image containing the WCS component which is to be used for the transformation.

If TRTYPE="EXPRES" is chosen then this parameter specifies the transformation that maps to the new X coordinate. The expression can contain constants, arithmetic operators ($+$,-,/,$\ast$,$\ast$$\ast$) and the functions described in SUN/61 (SIN,COS,TAN, etc.).

As an inverse mapping is not required in this application there is no need to use the X’=func(X,Y) form only func(X,Y) is required, however, the variables must be given as "X" and "Y".

If TRTYPE="EXPRES" is chosen then this parameter specifies the transformation that maps to the new Y coordinate. The expression can contain constants, arithmetic operators ($+$,-,/,$\ast$,$\ast$$\ast$) and the functions described in SUN/61 (SIN,COS,TAN, etc.).

As an inverse mapping is not required in this application there is no need to use the Y’=func(X,Y) form only func(X,Y) is required, however, the variables must be given as "X" and "Y".