[Shape-univ] couple of comments on the pixelization schemes

[Bartosz Lew]

Hi Boud, everyone

> > Anyway, at this time I see no point of terrible importance to force the
> > idea of the tetrahedron pixelization system so I drop this case. rather it
> > would be interesting to implement other pixelizations systems into the
> > isolat packet.
>
> Do you implementing "existing" pixelisation systems?
>
> Well, i see nothing against it, i just don't see it how it would be useful
> in practice. Unless someone is going to reanalyse the *raw* data of WMAP
> or Planck - and i mean the really raw data, before it has been converted to
> the healpix projection/pixelisation - then *re*formatting an observational
> map from the healpix system to a new system is only going hide the effects
> (if any) of the healpix system, it's not going to remove them. (And moreover,
> it will necessarily introduce some additional numerical error.)

unless of course you want to simulate your own maps to do various stuff -
the you can do it in different pixelization systems and see the
difference in power spectrum, bispectrum, Minkowski functionals etc.

for example see: astro-ph/0305537 for differences in power spectrum
and now I see another related paper which a haven't read yet:
astro-ph/0501494

besides I think there are methods for repixelizing from one scheme to
another which are more less optimall - free of the effects you mentioned
but I don't know the details.


>
>
> Hmm... However, given that a lot of interest is in the smaller angular
> scales, the question is how much different pixelisation methods could
> cause wrong conclusions to be made...
>
> If you're going to use these different systems e.g. on a hypothetical data
> set, which is projected/pixelised in different ways, then that could potentially
> be an interesting paper. :)
>

well, mayebe this isn't a big science :) but it's of basic importance.
However Healpix has been choosen as a pixelization system for PLANCK data
so probably they know what they are doing.

> OK, i'll put your isolat addition higher up in my todo list :)
well it's not urgent, take you time :)


and one more comment about the fortran versus c++.

I don't know why such a situation is but it seems to me that the
scientific society have choosen fortran (90) as a basic programming
language (eg. healpix, icosahedron, partially glesp pix. systems, WMAP
likelihood pipeline stuff, cmbfast -- all fortran ).
Maybe the point is that according to my last quick findings fortran is a
little bit faster to just faster :) evern if applied various
optimalization flags in c++ compiler.
But  for people who program in c++ (like me) the situation is not
comfortable, hence another motivation for writting implementations in
c/c++. (eg. cmbEASY was written in c++ AFAIR).

pozdr.
Bartek