Tuesday, March 28, 2006

Searching the sphere + looking for systematics


I hacked together a ra/dec searching code which uses the
htm (hierarchical triangular mesh) to match things on
the sphere. It is extremely fast. There is significant overhead
in finding the index for each input ra/dec position which is
a killer for small lists. For my work I always carry this
index around with all my objects, so I only generate it once.
But for a stand alone piece of code it is actually rather
annoying if not prohibitive. I don't know a workaround
for this yet.


I've been trying to track down systematics and haven't had any
luck with the easy stuff as I have described below. So what
I have done is remake the catalogs with more info
and stuffed it into my postgres database so I can very quickly
select source samples with different cuts and run them through the
lensing code. I think this is a better approach than adding
lots more info to the input catalog read by the lensing code
and then doing cuts within because the memory gets prohibitive
for the cheopsen at Chicago (limited to 2Gb). I'm finishing this
up now so tomorrow I'll start running the tests.

The first one I want to try is cuts on how well the galaxies are
resolved. I have done this test before and it passed, but maybe
the small number statistics of the LRGs and the high Ngal bin
is more sensitive to certain regions of sky where there is bad
seeing for example. Note the masking will be a bit messed
up if a resolution cut removes all objects from a given region
of sky.


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