[LSST|dm-astrometry #9] Re: update on the development of a simultaneous astrometry package

[Pierre Astier]

Le 19/05/2015 22:50, Jim Bosch a écrit :
> I think this looks like a great start, and I do think it'd be a good 
> idea to start integrating it into the stack as soon as possible 
> (though might depend on how much DM effort is available to help with 
> that).  I mostly agree with your ideas for other "next steps" - though 
> I don't think proper motion/parallax needs to be a top priority, and I 
> do wonder how much work it'd be to get better outlier rejection (would 
> we have to write our own custom low-rank Cholesky update?)
Hi Jim,

     Regarding small rank updates, I still have to figure out if this 
cholmod capability is provided
through the Eigen interface to Cholmod. If it is the case, It seems to 
me that a rank-2 update can
be turned into 2 rank-1 updates and this could be the easy way. I have 
not tried seriously
to talk directly to cholmod in C(++). One way I am considering is to 
switch to python
once we have the derivatives, and call all sparse algebra utilities from 
python. Marc and Nicolas
tell me that it is easy. One extra incentive to do so is that for non 
linear fits, the line search
is much easier to set up in python than in C++, and it will not make any 
difference for the execution
time, as long as traversing the measurements runs in C++.
     One thing I have not considered so far is to implement this 
capability into some existing
factorization code. It might turn out to be difficult.

      However, if the aim is to implement this simultaneous astrometry 
into the stack
ASAP (or sort of), efficiently clipping outliers is not a "must have".

>
> I imagine there will eventually be a lot of modification to what your 
> classes look like now in order to integrate them with existing LSST 
> classes with overlapping or related functionality.  But it might make 
> the most sense to just ignore most of that for now and just move this 
> into a new LSST package immediately, write some adapters to make it 
> accept inputs from the rest of the LSST pipeline, and then integrate 
> those individual classes one at a time later.
>

If time is a concern, this is the way to go. That's also much easier for 
me! Then, my next step
should be to dive again into the stack code and figure out mostly what 
are the interfaces to
the catalogs and Fits headers we should be using for that. I have not 
figured out yet what
the forces are in France for this effort. We are having a meeting next 
week where the question
will be raised.


Pierre.



>
> Jim
>
>
>
> On Tue, May 19, 2015 at 11:32 AM, Pierre Astier 
> <pierre.astier at in2p3.fr <mailto:pierre.astier at in2p3.fr>> wrote:
>
>     Hi,
>
>        Since our first phone conference about the development of a
>     simultaneous
>      astrometry package, I have coded a fit and ran a couple of tests
>     on exposure
>     sets from the CFHTLS and Suprime cam. I have described the work
>     and the first
>     results in a few slides that you can find at:
>     http://supernovae.in2p3.fr/~astier/sim-ast.pdf
>     <http://supernovae.in2p3.fr/%7Eastier/sim-ast.pdf>
>
>        I am mostly wondering whether this is enough to start discussing
>     how we practically implement the algorithms into the stack.
>
>     Pierre.
>
>     -- 
>     -------------------
>     Pierre Astier , LPNHE, 12-22 1er étage.
>     4 place Jussieu, F 75252 Paris Cedex 05
>     tel (33) 1 44 27 76 47  ---- fax (33) 1 44 27 46 38
>
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>
>


-- 


                   -------------------
Pierre Astier , LPNHE, 12-22 1er étage.
4 place Jussieu, F 75252 Paris Cedex 05
tel (33) 1 44 27 76 47  ---- fax (33) 1 44 27 46 38

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