User manual

 Finally, Aladin also know how to deal with an astrometrical calibration if the image
was loaded from a list that is in accordance to the Virtual Observatory Standard: SIA
(Simple Image Access, see 8.2 – supported data types).
Tip: In both first cases, the FITS header can be seen with the menu Edit => FITS
header.
An image can have several astrometrical calibrations, especially if you generated them
manually. To change from one astrometrical solution to the other, you need to display
the plane properties and to change the selection.
On the other hand, it the image does not have an astrometrical calibration, Aladin can
still generate views but will not be able to overlay sources or graphical additions with
celestial coordinates. Moving the mouse on such an image will simply write “No
astrometrical reduction” in the location band. It will however be possible to add graphical
overlays done manually (drawing by hand, marks, …) These overlays will have no other
coordinates than the XY coordinates in the image.
Creating/modifying the astrometrical calibration
Aladin enables you to create manually an astrometrical solution for an image that has
not got one. To do so, you need to select this image plane in the stack (click on its name)
and then use the menu “Image => Astrometrical Calibration …”.
The calibration window will first ask you to give a name for your new calibration.
Then, it will offer 3 methods to create/modify a calibration:
 By parameters;
 By matching stars;
 By WCS header.
Calibration by parameters
The first board displays basic parameters for
the astrometrical solution, i.e. a celestial
position and the corresponding pixel
coordinates in the image, the pixel angular
size, the projection method, a rotation angle
with respect to the north and at last, the
direction for which the right ascension
increases
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