Rotate the reference direction in a pair of Q and U images


This application creates a new pair of Q and U images from a supplied pair of Q and U images, by changing the polarimetric reference direction. The required direction can either be inherited from another NDF (see parameter LIKE) or specified as a specified axis within a specified coordinate Frame (see parameters AXIS and FRAME). It is assumed that the supplied Q and U images are aligned in pixel coordinates, and have the same reference direction.


polrotref qin uin qout uout like angle


Parameter AXIS is used only if a null value is supplied for parameter LIKE, in which case AXIS is the index of the axis within the coordinate frame specified by parameter FRAME that is to be used as the reference direction in the output NDFs. The first axis has index 1. [2]
A string specifying the co-ordinate Frame to which parameter AXIS refers. If a null parameter value is supplied, then the current Frame within the NDF specified by parameter QIN is used. The string can be one of the following:
  • A domain name such as SKY, SPECTRUM, 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). Using an SCS value is equivalent to specifying "SKY" for this parameter and then setting the System attribute (to "FK5", "Galactic", etc.) using KAPPA command WCSATTRIB. ["PIXEL"]

LIKE = NDF (Read)
A 2D Q or U NDF that defines the new reference direction. The supplied NDF should have a Frame with Domain "POLANAL" in its WCS component. The supplied Q and U images are modified so that they use the same reference direction as the supplied NDF. If null (!) is supplied, the rotation is defined by parametrer AXIS. [!]
QIN = NDF (Read)
The 2D input Q image. The WCS component of this NDF must contain a POLANAL Frame.
QOUT = NDF (Write)
The 2D output Q image.
UIN = NDF (Read)
The 2D input U image. The WCS component of this NDF must contain a POLANAL Frame.
UOUT = NDF (Write)
The 2D output U image.