User manual

manipulated like any other image in Aladin. The average will be used for regions that
overlap.
Cube or “animated sequence "
A data cube is displayed in Aladin as an animated sequence, i.e. image after image. The
logo in the stack is seen by a double line at its bottom as a symbol of the depth of the
cube. How to manage a cube is described in the section on “the view” in 5.1.2.
Tip: It is possible to add a new image to an existing data cube. To do so, you need to
click and drag the plane logo for the new image on the view where the cube is displayed.
After a short break, needed to resample the new image, the scrolling through the cube
will start again with an additional image.
5.11 Resampling images
Menu: Image => Resampling…
Principle
Even if it displays the same region on the sky, each image often has its own astrometrical
solution. This means that each specific pixel does not point necessarily at the same place
on the sky. To compare two images, pixel by pixel, it is often needed to resample one of
the two with respect to the other, called “reference image”. Basically, Aladin will go
through all the pixel locations in the reference image, deduce its coordinates on the sky,
and by using the astrometrical solution from the second image, at for each celestial
location previously found, it will deduce the pixel value, either the closest to the position
found, or a bilinear approximation of the 4 closest pixels. At the end of the process, you
will get two images on the same pixel “grid” for a unique astrometrical solution.
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