A particular orientation is specified in an HST Phase II proposal using yet another coordinate system: U2,U3. These axes are opposite to V2 and V3, so, for example, U3 = -V3. The angle ORIENT
, used in a Phase II proposal to specify a particular spacecraft orientation, is the position angle of U3 measured from North towards East. The direction of the V3 axis with respect to North is PA_APER
- y and so
The IRAF task rotate in the package images.geom takes an image and rotates it counter-clockwise by a specified angle. To orient an image so that its y axis becomes North, the angle to specify is PA_APER
. The x axis will then point approximately 5º North of East. Orientations can be checked by using the Visual Target Tuner
(VTT) in the APT
.
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