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While the shift file looks nearly identical to the prior run, 
this is because the axis-dependent rotation 
and scale values are averaged together in the shiftfile. 
To determine the actual values, it is necessary to inspect the logfile.

j9irw5kaq  SCALE_X: 1.000008792  SCALE_Y: 1.00000757  ROT_X: 0.002818152  ROT_Y: 359.998708  SKEW: 359.9958898
j9irw4b1q  SCALE_X: 0.999986877  SCALE_Y: 1.00003072  ROT_X: 0.004877188  ROT_Y: 0.00405990  SKEW:  -0.0008173   

The above script is related to the axis explanation of fitgeometry=general of drizzlepac.tweakreg.TweakReg. (and this is from DrizzlePac tutorial)

How are there two different rotation with respect to "x axis" and "y axis"?

In two-dimensional space, there is just one rotation with x-axis and y-axis separately, NOT two rotations.

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  • $\begingroup$ Screenshots of text are strongly discouraged in Stack Exchange, especially when you can just copy/paste the actual text. If you add four spaces in the beginning of the line your code-like items will display as a code block (equal spaced font) like this. Thanks! $\endgroup$
    – uhoh
    Aug 6, 2022 at 12:03
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    $\begingroup$ Two possibilities: 1. The ROT_X and ROT_Y values differ by less than the errors, and so are not actually different; 2. A real difference could be an indication of a distortion, which cannot be accurately represented by a uniform rotation. $\endgroup$ Aug 6, 2022 at 14:30
  • $\begingroup$ @ago Thank you for good comment. I edited it. $\endgroup$
    – BAO
    Aug 7, 2022 at 0:32
  • $\begingroup$ @PeterErwin Thank you, but what's the meaning of uniform rotation of "possibilities 2"? Can we rotate the x-axis and y-axis separately? $\endgroup$
    – BAO
    Aug 7, 2022 at 0:35

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