[OpenLayers-Users] Best approach for sky map

[Phil Scadden]

On 27/02/2014 7:36 a.m., bnorman wrote:
>
> I would like to use openlayers to display a map of the sky using 
> custom imagery. I plan to use geoserver on the back end.
>
> Ideally, I would like:
>
>   * Display units of right ascension (in hours 0 to 24 hours),
>     declination (-90 to 90 degrees)
>   * Seamless scrolling across the right ascension boundary (0/24 hours)
>   * Seamless scrolling across the poles
>   * Use of image tiles (ultimately converted from FITS files) in
>     quadrilateralized spherical cube (QSC) or HEALPIX projection. Both
>     of these are available in PROJ4. I'm not sure how to store these
>     tiles, because those projections don't necessarily work with GEOTIFF.
>   * Vector overlays (star maps, etc).
>

If you settled for scrolling across the RA boundary but not the 
scrolling across the poles, it would make life simpler. I am not sure 
how you would do both without modifying OL code. The projections also 
look a little challenging. The forward projection from RA,D -> x,y is 
straightforward enough but as users pan the map, you are have to do the 
reverse projection all the time and with an interrupted projection, that 
sounds "interesting". The absolute key to this is going to the 
processing that inverse projection.

I'm interested. I have battled away at OL on the dateline issues and at 
Geoserver on the same thing. As far as I can see, they both have 
fundamental concept of "Extent" rectangle with maps the mapframe 
rectangle in screen coordinates to projection coordinates. There is 
assumption that
RH>LH,  and inequality equation for top/bottom is constant. Various 
checks in the code cope with the 180 line. Inhouse software used for 
geophysical mapping deals with various cases of the Extent rectangle 
defined by the inequality relations between left/right top/bottom. These 
different cases generated different "working coordinates" for the Extent 
used to the drawing maths, but panning etc carefully adjusts the Extent 
rectangle to working on sphere rather than flat earth assumption. It 
would interesting to see what would be involved in working that into OL. 
This is something that I think you need.

I would rather like to be able to pan seamlessly down from NZ to the 
Ross dependency and across the pole. This would be same issue that you 
are dealing with.

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