Presentacin de PowerPoint

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GAIA Simulator Development Example A Java code
for Fundamental Algorithms
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• The GAIA Simulator structure
• Simulator is not GDAAS
• GASS
• GIBIS
• Common Libraries
• Java language
• Portability modular structure as priorities
• Speed ,Performance and Read-at-Once
• Wrapping from C/C Fortranto Java
• Conclusions

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The GAIA Simulator structure
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• Simulator is not GDAAS

GDAAS is the ESA contract which has to solve the
problem of the GAIA reduction process, giving as
a final result a closed, tested package capable
of reduce the 5 years mission data in a
reasonable time and in a robust self-consistent
way (Global Iterative solution).
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GASS GAIA System Simulator GASS is designed to
simulate the telemetry stream of the GAIA mission
according to the GDAAS (Gaia Data Access and
Analysis Study) specifications, using models of
the astronomical objects and instruments. GASS
has a Grafic User Interface and must be
downloaded with a compilable version of the whole
simulator to run properly
GIBIS GAIA Image and Basic Instrument Simulator
Generates images of all sky features (stars,
galaxies, nebulas, background,etc...) as seen by
the intruments (at the pixel level) with the aim
of develop Quick-look routines, classification,
and on-board detection of all kind of objects and
events. GIBIS has a web interface which allows
you to send queries via internet. http//www.ast.c
am.ac.uk8080/gibis
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It is planed to release a full compiled and
documented version of the whole
GASS simulator v2.0
It will be distributed in a few weeks (under
request) Coordinator Eduard Masana,
emasana_at_am.ub.es
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http//www.ast.cam.ac.uk8080/gibis
GIBIS v1.4 has a fully functional version
throught the internet (password needed)
pixel level simulator images
Coordinator Carine Babusiaux,
carine_at_ast.cam.ac.uk
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Recent meeting information and other documents
(Simulator documentation, User guides,etc.) are
going to be available through SWG web page
http//gaia.am.ub.es/SWG/
To access SWG Work Area, please send an e-mail to
Xavier Luri xluri_at_am.ub.es
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• Common Libraries (gaiasimu package)

Both simulator efforts use the same libraries in
order to preserve consistency and to save time
duplicating job.
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This libraries are in a package called gaiasimu,
which contains the univers models,satellite and
intruments models, all required routines, as well
as the the used numerical libraries. It is
expected this libraries being flexible and
portable enough to allow the community use them
for their particular simulation purposes (i.e
supernova and other event detection, stocastic
microlensing noise, variability detection, etc.)
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Java the language of the Simulator
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• Portable and Modular as a development priority

Algorithm and routines implementation must be as
flexible as possible to allow its generic
implementation in any of the present/future
simulator efforts. The code must be portable. It
could run in any machine with identical
results. The code must be modular. Diferent parts
are developed by diferent groups and are being
integrated in the same structure. In the same
philosophy, the code must be efficiently
documented. Documentation can be found at SWG web
page
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• Performance, speed and Read-at-Once

The use of temporary files is HIGHLY not
recomended. If a routine must read from a file a
set of parameters it is recommended to
Read-at-Once the file at the first time the
routine is initialised.
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• Wrapping from C/C and Fortran to Java

If an algorithm is a bottle neck or its
translation is very complicated, Java allows
wrapping from other languages. Wrapping must be
avoided if it is not considered essential,
because it makes the Simulator lose its
portability...
... and because the people working in the
Simulator structure should have to wrap the
routines themselves.
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An example Fundamental Algorithms
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• What are the Fundamental Algorithms?

• The so-called Fundamental Algorithms (LL-44) are
  those equations/processes which relate
  observations with catalog astrometric data.
• Due to the nominal high precission astrometry
  stated for GAIA, a full relativistic treatment of
  the observation process must be carefully tested
  and developed.

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In this process there are some independent tasks
involved Main Task Observables
parametrization (parallax, and proper motions,
solar system objects orbits), Gravitational
Light deflection and relativistic aberration
modelization Related Tasks - Reference Frames
definition - Satellite ephemeris model (position
, velocity) - Solar System model (postion and
velocity of relevant massive bodies). Eventually,
other object properties may be required from the
model. - Time transformations (i.e simulated
telemetry data MUST be given in satellite proper
time) - Attitude parametrization
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• Parameters review and interactions

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Baricentric position at Observation Time
source position source velocity tobs
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Parallax Correction
source position source velocity tobs observers
position
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Gravitational light deflection
source position source velocity tobs observers
position solar system ephemeris Gamma ppn
parameter
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Observed direction (aberration correction)
source position() source velocity() tobs() obse
rvers position observers velocity solar system
ephemeris Gamma ppn parameter
tobs()
Satellite Proper Time
S vector
Field Of view Angles
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source position() source velocity() tobs() ob
servers position observers velocity solar
system ephemeris Gamma ppn parameter
tobs()
Satellite Proper Time
S vector
Field Of View Angles
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Input parameters
Satellite ephemeris
Solar System Model
Global Parameters
Time ephemeris
Attitude
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Input parameters
Satellite ephemeris
Fundamental Algorithms Main Task
Solar System Model
Global Parameters
Time ephemeris
Attitude
?, ? , ?
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Fundamental Algorithms Main Task
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What the Simulator people has to say about....
Fundamental Algorithms Main Task
Routines will not have direct acces to
perpendicular models, if they are not coded in
Java
In this case, access has to be provided by a GAIA
Simulator interface coded in Java. This impose to
such routines to be as much parametric as
possible
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The Simulator interface is partially done waiting
to be decide the final structure I/O methods. For
test purposes it has been implemented a Java
version of S.A.Klioner routines following the
presented structure for the F.A.Core Tasks.
Fundamental.java
Observer.java (satellite ephemeris) SolarSystemMod
el.java (solar system massive objects ephemeris)
If it is all intilialised correctly, a call of
getDirectionOnSatellite(double tobs, double
x, double v) return the desired S vector.
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Some reference performance results
Some simple test permormed with diferent
configurations Only Sun, Only Jupiter , Sun
Jupiter
This tests have shown that the numerical
stability is guaranted at ?as precision working
at 64 bits precision (theoretical defelction has
been obtained using
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Some initial rounding problems at the time to
estimate ?? were solved using an aproximate rule
to calculate the angle between to very similar
unit vectors
Because of initial rounding problems we tryed to
perform all calculations at arbitrary
precission. When the rounding problems were
solved in final angle estimation, arbitrary
precision showed to give almost the same results
as working in standard 64bits.
- Using arbitrary precision operations 12000 sec
/ 106 stars 12.1 miliseconds per star   - Using
double precision operations 105 sec / 106 stars
0.105 miliseconds per star
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• CONCLUSIONS

• From the GAIA Simulator point of view, the
  Perpendicular model a Java Interface is the
  best option to keep the modular structure.
• It allows to develop such models independently
  from F.A.

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Chevychev representation ? To be defined
Time ephemeris

• As a crucial part of the telemetry production, a
  decision must be taken.
• To proceed with the time integration it is needed
  a Solar System model for ephemeris compatible
  with the satellite ephemeris.