Native support for MOC operations in the Java HEALPix package

[Martin Reinecke]

Hi again,

I did some further experiments with the HEALPix MOC implementation and
noticed that the MOC sizes (i.e. the number of pixel intervals in a MOC)
can be reduced by roughly 20% on average if one uses a
Peano-Hilbert-ordering of the pixels on the sphere instead of the more
conventional NEST ordering.
Support for this kind of ordering has been in the HEALPix C++ package
for many years now, and porting it to the Java package was a matter of
half an hour.

Would there be interest in such a kind of MOC?

Once generated, the MOC objects would behave in exactly the same way as
the currently used MOCs in NEST scheme, they would just be smaller and
operations on them would be faster.
Conversion between MOCs in Peano and NESTED representations is possible,
but fairly slow.

Regards,
  Martin

On 10/15/14 14:16, Martin Reinecke wrote:
> Hi,
> 
> I was encouraged by Pierre Fernique to send this announcement to the
> IVOA apps mailing list, since there might be broader interest ...
> 
> 
> After the MOC standard document had been accepted, I started working on
> native MOC support in the Java HEALPix package.
> My aim was to provide a compact and highly efficient implementation of
> the central functionality (MOC construction, input/output and set
> operations). Here is a fairly complete list of the current capabilities:
> 
> - import/export from/to FITS (both files and streams are supported)
> 
> - import/export from/to strings (both the basic ASCII and JSON syntax
> shown in the MOC standard)
> 
> - import/export from/to a highly compressed bitstream representation,
> making use of interpolative coding. These objects are significantly
> smaller than the FITS and ASCII representations, and can be read/written
> very quickly; they could be useful on a VO server dealing with many MOCs
> at the same time.
> 
> - import/export from/to RangeSets of UNIQ pixels
> 
> - set operations (union, intersection, subtraction, overlap test, subset
> test, complement) that are even faster than what was available so far,
> due to improvements in the RangeSet class.
> 
> - resolution degradation of a MOC to a desired Healpix order. Partially
> covered pixels can be kept or discarded, depending on a parameter.
> 
> If you are interested, I have attached a source tarball of the current
> Java HEALPix package. The most up-to-date version can always be found in
> the subversion repository at http://sourceforge.net/projects/healpix
> 
> Please let me know if you think that essential functionality is still
> missing!
> Concerning class and function names, I'm still considering various
> alternatives to make them as unambiguous as possible. Again, if you have
> suggestions in that area, please tell me.
> 
> Best regards,
>   Martin Reinecke
>