Aladin Lite beta version, fixing astrometry offsets

[Thomas Boch]

Dear all,

We are releasing a beta version of Aladin Lite, which fixes some offsets 
which were visible on regions with
strongly distorted HiPS tiles.
This improvement was needed and awaited by several projects -- it will 
of course benefit all Aladin Lite users

You can see the new version in action on these 2 test pages:
- http://cds.unistra.fr/~boch/AL/test-reduce-deformations.html  : the 
view is centered on M81. If you disable the offset-correction by 
deselecting the checkbox, you will see how this region was rendered 
before the improvement.

- http://cds.unistra.fr/~boch/AL/test-reduce-deformations2.html  : the 
polyline shows the Cassiopeia constellation.When disabling the 
correction, you will notice the offset between the stars position and 
the underlying image HiPS.

If you have a tool which makes use of Aladin Lite, you are encouraged to 
test this new version and provide feedback. Javascript and CSS files are 
available at 
http://aladin.u-strasbg.fr/AladinLite/api/v2/beta/aladin.min.js and 
http://aladin.u-strasbg.fr/AladinLite/api/v2/beta/aladin.min.css

The correction updates the ways HiPS are drawn in Aladin Lite, which now 
uses the same algorithm as Aladin Desktop. HiPS by themselves stay 
untouched. The new code does not seem to slow down the global rendering, 
at least on the platforms I tested (Ubuntu + MacOS with latest versions 
of Chrome and Firefox). Your tests are welcome to check if this remains 
true on other setups.

I will present a few slides about this improvement at next week Interop 
(Apps 2 session, on Thursday afternoon).

Cheers,
Thomas