Hi Jacek,
Kem's in the air at the moment, so I'll try to reply for him. The
first two factors affect only the sizes of the template images. The
1.3 factor affects both the template images and the number of objects in
the object table. There might even be an argument for the color factor
to be greater than 2.
Tim
Jacek Becla wrote:
Hi Kem,
(Probably I am the only one that does not know this)...
can you explain how the multiplications you mentioned:
> x2 for color information
> x2 for float
> x1.3 for spare field/filters for unpredicted weather/seeing backup
will influence the number of objects in the Object table?
Based on Tim's email, we will be dealing with
1000 fields * 150,000 * 10sq deg = 1.5 billion objects
per night. Do I need to multiply this number by your
x2, x2 and 1.3?
Thanks,
Jacek
Kem Cook wrote:
Hi Tim and Jacek,
Just to play devil's advocate, we may need quite a bit more than 6 TB of
template images. While we may only take 1000 images between
astronomical
twilights, we may not be able to accurately predict which fields and
filters these will be. Variable conditions may push us to observe
fields
which are lower priority. We may also do z and y observing in twilight
conditions which gives us a few hundred more field/filter
combinations. We may also need color information for diffraction
correction
calculations. Might we also need our templates to be better than
integer
precision?
Baseline with twilight observing:
1200 images x 6.4 GB/image X 0.80 unique area = 6.1 TB perfect planning
x2 for color information
x2 for float
x1.3 for spare field/filters for unpredicted weather/seeing backup
gulp, 31.7 TB (! upper limit, I hope)
Kem
Hi Jacek,
Here's a rough calculation. I assume a typical night of 10 hours,
which corresponds to about 1000 observations of distinct fields (sky
positions). For each of those sky positions, we need at the base:
a) Template images for the fields. At roughly 6 GB/image, that
gives us
6TB
b) Recent catalog data for all objects in the fields brighter than
about
V=25. How much data that is will vary quite a bit, as a previous email
I sent out explains in some detail. For present purposes, I assume
that there are 150000 objects/deg^2 that qualify. I assume that for
each object we need summary information, which I estimate at 200 bytes
(very rough), and the latest 10 epochs of measurements at 50 bytes
each.
This then gives us 1000 fields * 150000 * 10sq deg * (200 + 10*50) =
1.5TB. I'd say at present this is no better than a factor of two
estimate.
c) calibration images - this is maybe 100GB, negligible.
So a rough guess is 7.5TB.
Cheers,
Tim
Jacek Becla wrote:
Jeff/Tim/Ray
I'd like to start thinking about details of pre-staging
data at the base / partitioning it, but before I do that
I need to understand how much data we are talking about
per night (the question was brought up at today's Database
telecon).
If you could find that out and give me even a rough estimate
whether it is a terabyte or a hundred terabytes, that
would help a lot.
Thanks,
Jacek
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begin:vcard
fn:Tim Axelrod
n:Axelrod;Tim
org:;Large Synoptic Survey Telescope
email;internet:[EMAIL PROTECTED]
title:Data Management Project Scientist
tel;work:520-322-8735
version:2.1
end:vcard
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