the gaia system simulator june 2003rrfwg meeting at dresden gaia simulator development example a...
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June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
GAIA Simulator Development Example
A Java code for Fundamental Algorithms
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
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
An example : Fundamental Algorithms
•What are the Fundamental Algorithms?
•Parameters review and Interactions with other Simulator Parts
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
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).
GAIA Simulator is an “independent” effort to provide the input Raw data to GDAAS contract and other development efforts.
People working with the simulator spent their “scientific” time in the development of this tool.
•Simulator is not GDAAS
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
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.cam.ac.uk:8080/gibis
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
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, [email protected]
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
http://www.ast.cam.ac.uk:8080/gibisGIBIS v1.4 has a fully functional version throught the internet (password needed)
Coordinator : Carine Babusiaux, [email protected]
pixel level simulator == images
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
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 : [email protected]
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
•Common Libraries (gaiasimu package)
Both simulator efforts use the same libraries in order to preserve consistency and to save time duplicating job.
gibisgass
gaiasimu
gaia(from gaiasimu)
universe(from gaiasimu)
utils
g l o b a l
(from gaiasimu)
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
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.)
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
•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
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
•Performance, speed and Read-at-Once
The portability of Java (not machine dependent) have some essential counterparts. For example, the maximum precision you can use (using basic algebraic manipulation) is 64 bits :
long : integer value
double : floating point value
Java is not so fast as other languages (as Fortran or C/C++) in some specific tasks (I/O from files for example).
1 bit sign + 63 bits mantise
1 bit sign + 63 bits mantise +1 bit sign + 7 bits exponent
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.
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
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...
•Wrapping from C/C++ and Fortran to Java
... and because the people working in the Simulator structure should have to wrap the routines themselves.
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
•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.
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
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
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
source positionsource velocitytobs
Baricentric position at Observation Time
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
source positionsource velocitytobs
observer’s position
Parallax Correction
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
source positionsource velocitytobsobserver’s positionsolar system ephemerisGamma ppn parameter
Gravitational light deflection
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
source position(*)source velocity(*)tobs(*)observer’s position observer’s velocitysolar system ephemerisGamma ppn parameter
tobs(*) Satellite Proper Time
S vector Field Of view Angles
Observed direction (aberration correction)
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
source position(*)source velocity(*)tobs(*)
observer’s position observer’s velocity
solar system ephemeris
Gamma ppn parameter
Solar System Model
Satellite ephemeris
Input parameters
Global Parameters
tobs(*) Satellite Proper Time
S vector Field Of View Angles
Time ephemeris
Attitude
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
Input parameters
Satellite ephemeris
Solar System Model*
Global Parameters
Time ephemeris
Attitude
Generated by the Universe Models (Galaxy model ; Torra et Al)
Chebychev representation (F.Mignard GAIA-FM-13)
Chebychev representation ? (F.Mignard To be done)
General Relativity = 1.0 (A. Einstein)
Chevychev representation ? To be defined
Quaternion formalism (L.Lindegren)
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
Input parameters
Satellite ephemeris
Solar System Model*
Global Parameters
Time ephemeris Attitude
, ,
Fundamental Algorithms Main Task
Perpendicular Models
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
Fundamental Algorithms Main Task
Pure PPN perturbative formalism (S.A.Klioner et al)
General Relativistic “semi-analítical” approach (F.de Felice, A.Vechiatto et al.)
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
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
What the Simulator people has to say about....
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
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)
SolarSystemModel.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.
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
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 :
21
2
ctgrc
GM
o
i
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
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 :
43
24
1' Onn
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
Intel P4 [2.4 GHz]
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
- I/O flow must be decided being this fact independent of the implementation chosen.
-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.
•CONCLUSIONS
June 2003 RRFWG Meeting at Dresden
The GAIA System Simulator
Time ephemerisChevychev representation ? To be defined
-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.