Pierre Fernique, Thomas Boch,Anaïs Oberto, François Bonnarel
Centre de Données astronomiques de Strasbourg

P.Fernique – T.Boch – A.Oberto – F.Bonnarel – ADASS 2009/Sapporo

21e century tools

P.Fernique – T.Boch – A.Oberto – F.Bonnarel – ADASS 2009/Sapporo

Browsing the sky...
2001

Virtual Sky http://www.virtualsky.org

2006

Wikisky/sky-map http://sky-map.org

2006

World wind http://worldwind.arc.nasa.gov

2007

Google sky http://earth.google.com

2008

WWT http://www.worldwidetelescope.org

2008

VIRGOhttp://archive.eso.org

2009

Aladin http://aladin.u-strasbg.fr=> 21st century tools

P.Fernique – T.Boch – A.Oberto – F.Bonnarel – ADASS 2009/Sapporo

The 4 main issues
1)The size of data ( server-side, via internet, client-side)2)The client display performances
3)The data base structure (storage and retrieval)4)The sky projection/distorsion

1) Data size...
●

DSS2: 1 arcsec/pixel resolution survey●=> 500 billions pixels => 1 TB in 16 bits/pixel=> 70 GB in JPEG
●Resampling whole DSS2 takes now 2 monthsof elapsed time for computation on a basicmachine●A few MB in a few seconds via internet« Traditional » surveys seem not so big today !
P.Fernique – T.Boch – A.Oberto – F.Bonnarel – ADASS 2009/Sapporo2) Client display performances...
●

Current graphics cards require ~1ms for projecting
1million pixels (bilinear method)=> 20 ms for redrawing an all sky view
with one thousand (64x64) mosaic images=>You can drag&drop the sky with the mouse=> Thanks to computer games
P.Fernique – T.Boch – A.Oberto – F.Bonnarel – ADASS 2009/Sapporo

3 & 4) How to « divide » the sky ?
●Server database => get a good spatial index●Client => get an efficient display (poles ?, pixelvalue ?...)
Aladin choice

P.Fernique – T.Boch – A.Oberto – F.Bonnarel – ADASS 2009/Sapporo

Our goal
Offer an All sky mode providing the samefunctionalities that the classical « image » mode(catalog overlays, survey comparison, all projections, constrast
adjustement, pixel manipulation, local data...)Halphaall sky

IRAS-IRIS
100 all sky

P.Fernique – T.Boch – A.Oberto – F.Bonnarel – ADASS 2009/Sapporo

HEALPix●Sky splitted in 12 diamonds divided in 4 subdiamonds recursively
Norder01:
6:
89:
12:
18:
29pixels
1248
:
49152
:
7864323145728:
201326592:
8,25E+011:
3,46E+018

16bits JPEG Pix res Missions
24B
58,63°
96B
29,32°:
96KB
6KB 54,97' COBE:
1,5MB 100KB 13,74' WMAP
6MB 400KB 6,87' PLANCK:
384MB 25MB 51,53'' IRAS, ROSAT:
1,5TB 100GB 0,255'' DSS, 2MASS, SDSS:6HB 410PB 124mas Healpix 64 bits limit

P.Fernique – T.Boch – A.Oberto – F.Bonnarel – ADASS 2009/SapporoWhy did Aladin choose HEALpix ?
●Regular hierachical sky division (easy server
implementation – no pole problem)●Pixel equal area => fast pixel algorithms●Immediate conversion (pixel number to coordinates)with no recursion => constant time
double[] pix2ang(long nside, long ipix)●

FITS format for recording HEALPix allsky map =>direct usage for current mission data such as Planck●

HEALPIX libraries in FORTRAN, C, C++, IDL, Java (inour case N. Kuropatkin code)

P.Fernique – T.Boch – A.Oberto – F.Bonnarel – ADASS 2009/Sapporo

On server side...
●Actually no data base, just directories and files(1024x1024 square « tiles » in FITS or JPEG=> 786432 files for DSS/order18, 768 files for IRIS/order3)●

From a HTTP server or directly on the clientmachine●

Full and compressed pixels supported

P.Fernique – T.Boch – A.Oberto – F.Bonnarel – ADASS 2009/Sapporo

On client side...
●●Retrieving Healpix diamonds
corresponding to the current
user view and resolution●Immediate Healpix computation for determining which healpix
pixels are in a sky region for a given depth order,●Filepath/url immediately built from survey/order/pixelNumber
triplet => no «localisation» query required)

Drawing each diamond for fully covering the 4
projected polygon corners (according to the user-definedprojection – Sinus, Tangential, Arc, Aitoff, ZET, Stereographic,Cartesian...)P.Fernique – T.Boch – A.Oberto – F.Bonnarel – ADASS 2009/Sapporo

Local full sky file feature●HEALPix FITS map fileautomatically recognized by Aladin●Directory tree (= virtual « Database ») built locally at first loading
and kept for next usage=> ex : WMAP - 50MB process in 12s

P.Fernique – T.Boch – A.Oberto – F.Bonnarel – ADASS 2009/Sapporo

2 mn demo...
P.Fernique – T.Boch – A.Oberto – F.Bonnarel – ADASS 2009/Sapporo