Rotate qpoe image around an axis perpendicular to the image, normally about the origin (0,0). The angle of rotation is specified in degrees counter-clockwise. The sample shows rotation of the qpoe image by 20 degrees.
cl> xray xr> ximages xi> qprotate input qpoe file name: xdata$snr.qp region descriptor: <cr> angle through which to rotate (0.): 20 output qpoe file name: xnr.rot.qp event definition (large): <cr>
The output qp file is generated with the same dimensions as the input, even when a region is applied. If no region is used, the translation may result in the loss of part of the image and a list of discarded events will appear. Note that QPEX warnings can be safely ignored.
One practical application of qprotate is to align qpoe images in which the satellite had different roll angles. Two qpoe images can be aligned by rotating each of them by the negative of their roll angles. The roll angle, if present in the header, will be found in the parameter XS-DANG. This can be found by running qphedit, in the ximages package. For example, to find the roll angle of xdata$snr.qp, type:
xr> ximages xi> qphedit xdata$snr.qp XS-DANG The task will output the line:
Then qprotate can be run on the qpoe file using +51.3059 as the angle. Applying the same process to another qpoe image will cause the support structure of the instrumentation to line up. Note that the roll angle is not available in all cases. When it is not, the parameter XS-DANG will generally have the value 0.0.