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SKY-MAP.ORG / WIKISKY • View topic - Finding the projection

Finding the projection

Finding the projection

Postby tablegnome » Wed Mar 09, 2011 6:07 am

Hi
This is one of the best places i've found to get nice pictures of the sky.
My only problem is that once i zoom in i have no idea of the projection used.
The full sky map i guess is an aitoff projection (or possibly hammer)
I assume the zoomed in version is an azimuthal equidistant projection but i cant find a way of finding the parameters.
tablegnome
 
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Re: Finding the projection

Postby admin » Fri Mar 11, 2011 2:00 pm

tablegnome wrote:Hi
This is one of the best places i've found to get nice pictures of the sky.
My only problem is that once i zoom in i have no idea of the projection used.
The full sky map i guess is an aitoff projection (or possibly hammer)
I assume the zoomed in version is an azimuthal equidistant projection but i cant find a way of finding the parameters.


That's correct - full sky is in aitoff, and zoom-ins are in azimuthal equidistant projection.
The center for azimutal projection when you just open new location or zoom-in/out is chosen to be closest to center of view with rounding by 20 degrees (for image drawing caching optimization).
You can see what center is currently used by checking parameters of any tile, i.e.
Code: Select all
http://wikisky.org/imgcut?survey=DSS2&img_id=all&angle=1.25&ra=1.33333333333333&de=40&x_shift=-1408&y_shift=384

Here the center is RA=1.333h, Dec=40 deg.
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