Hi Jacek,
I think of the object catalog having two logically distinct pieces.
The first is the time-independent information about an object, which
I've sometimes referred to as summary information. This contains best
estimates on object position, shape, colors, classification, proper
motion/parallax, etc, and is updated relatively infrequently at the
archive. The second piece is all the individual measurements over time
that are associated with the object. The summary information is roughly
equivalent to the SDSS catalog. I agree with Jim: we need a lot more
than the 200 bytes I quoted for this. We're likely to be larger than
SDSS simply because we will likely have a more ambitious shape
description scheme for extended objects. This should all drop out of
the LSST schema definition - we need to devote more attention to it!.
We should be able to estimate the size of the second, time-dependent
piece much more easily - my 50 byte number is probably not too far off.
BTW, I think all this email traffic should go out to LSST Data - it is
useful for others to see and possibly comment.
Tim
Jacek Becla wrote:
Tim/Kem
I exchanged some emails with Jim Gray and he pointed out
that the SDSS objects are about 2KB each (while ours are
124 bytes, at least in the precursor schema, and you (Tim)
mentioned ~250 bytes.
He then said that:
Jim Gray wrote:
All I can say is that the SDSS is in 5 bands and every number has an
error associate with it And then there is a summary value. So every
value is 12 values. That is how things are 12x what I would have
guessed.
In addition the pipeline gereates LOTs of flags. But there are about
70 "popular" fields out of the 400. So we have a 8x smaller "tag"
table that is only about 300 bytes/object.
Hard for me to say if LSST will be different. You might ask them.
So here I am checking...
thanks,
Jacek
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fn:Tim Axelrod
n:Axelrod;Tim
org:;Large Synoptic Survey Telescope
email;internet:[EMAIL PROTECTED]
title:Data Management Project Scientist
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