> GAIA completely understands the WCS in these images but does not
> attempt to rotate the image in order to put North at the top. If the
> issue is simply 90 degree rotations or flips you can click on the
> little flip/rotate arrows at the top of the GAIA display.
>
> I'm surprised that DS9 resamples the image in order to always display
> North up.
DS9 doesn't always display North up - by default ds9 behaves the same as
gaia in this regard, but it does have a feature that with a single click
it will it display the image north up, east left, whatever arbitrary
rotation angle or flip is required to do so.
This is actually an incredibly useful feature, especially when observing
at telescopes such as Gemini where PIs are able to and often do set
arbitrary (ie non 90-degree based) instrument position angles for both
imaging and spectroscopy.
Also it's very useful when you want to visually compare data taken in
different orientations without explicitly resampling the data file.
Space based data (eg HST, Chandra, Spitzer) is often at arbitrary roll
angles, and this feature makes quick assessment of "do I see that blob
in the other data" questions a lot easier if you don't have to do the
de-rotation mentally... :-)
To some extent Gaia does 'resample' in order to display different zoom
levels - I know that's a lot simpler transformation, but it's not like
there's currently a hard 1:1 mapping from data pixels to display pixels.
This feature being one of the few reasons I do find myself using ds9
sometimes, I would be really happy to see Gaia support a feature like
this.
Also, for what it's worth, we at Gemini are currently deciding what
display tools we'll support for observing and data reduction in the
future. I'd very much like Gaia to be a serious contender in this, but I
do think the majority opinion will be that an option to display
north-up, east-left with a single click and arbitrary rotation angles
has to be a hard requirement.
Cheers,
Paul.
> To regrid an image to align it with it's coordinate system you can use
> KAPPA REGRID and provide a null mapping (where null means "!"). This
> works for arbitrary rotation angles.
>
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