1. The GAIA System Simulator June 2003RRFWG Meeting at Dresden GAIA Simulator Development Example A Java code for Fundamental Algorithms

2. The GAIA System Simulator June 2003RRFWG Meeting at Dresden 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

3. The GAIA System Simulator June 2003RRFWG Meeting at Dresden The GAIA Simulator structure

4. The GAIA System Simulator June 2003RRFWG Meeting at Dresden 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

5. The GAIA System Simulator June 2003RRFWG Meeting at Dresden 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

6. The GAIA System Simulator June 2003RRFWG Meeting at Dresden 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@am.ub.es

7. The GAIA System Simulator June 2003RRFWG Meeting at Dresden http://www.ast.cam.ac.uk:8080/gibis GIBIS v1.4 has a fully functional version throught the internet (password needed) Coordinator : Carine Babusiaux, carine@ast.cam.ac.uk pixel level simulator == images

8. The GAIA System Simulator June 2003RRFWG Meeting at Dresden 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@am.ub.es

9. The GAIA System Simulator June 2003RRFWG Meeting at Dresden Common Libraries (gaiasimu package) Both simulator efforts use the same libraries in order to preserve consistency and to save time duplicating job.

10. The GAIA System Simulator June 2003RRFWG Meeting at Dresden 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.)

11. The GAIA System Simulator June 2003RRFWG Meeting at Dresden Java ; the language of the Simulator

12. The GAIA System Simulator June 2003RRFWG Meeting at Dresden 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

13. The GAIA System Simulator June 2003RRFWG Meeting at Dresden 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.

14. The GAIA System Simulator June 2003RRFWG Meeting at Dresden 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.

15. The GAIA System Simulator June 2003RRFWG Meeting at Dresden An example : Fundamental Algorithms

16. The GAIA System Simulator June 2003RRFWG Meeting at Dresden 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.

17. The GAIA System Simulator June 2003RRFWG Meeting at Dresden 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

18. The GAIA System Simulator June 2003RRFWG Meeting at Dresden Parameters review and interactions

19. The GAIA System Simulator June 2003RRFWG Meeting at Dresden source position source velocity tobs Baricentric position at Observation Time

20. The GAIA System Simulator June 2003RRFWG Meeting at Dresden source position source velocity tobs observer’s position Parallax Correction

21. The GAIA System Simulator June 2003RRFWG Meeting at Dresden source position source velocity tobs observer’s position solar system ephemeris Gamma ppn parameter Gravitational light deflection

22. The GAIA System Simulator June 2003RRFWG Meeting at Dresden source position(*) source velocity(*) tobs(*) observer’s position observer’s velocity solar system ephemeris Gamma ppn parameter tobs(*) Satellite Proper Time S vectorField Of view Angles Observed direction (aberration correction)

23. The GAIA System Simulator June 2003RRFWG Meeting at Dresden 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 vectorField Of View Angles Time ephemerisAttitude

24. The GAIA System Simulator June 2003RRFWG Meeting at Dresden 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)

25. The GAIA System Simulator June 2003RRFWG Meeting at Dresden Input parameters Satellite ephemeris Solar System Model* Global Parameters Time ephemerisAttitude , ,  Fundamental Algorithms Main Task Perpendicular Models

26. The GAIA System Simulator June 2003RRFWG Meeting at Dresden 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.)

27. The GAIA System Simulator June 2003RRFWG Meeting at Dresden 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....

28. The GAIA System Simulator June 2003RRFWG Meeting at Dresden

29. The GAIA System Simulator June 2003RRFWG Meeting at Dresden 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.

30. The GAIA System Simulator June 2003RRFWG Meeting at Dresden 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 :

31. The GAIA System Simulator June 2003RRFWG Meeting at Dresden 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 / 10 6 stars = 12.1 miliseconds per star - Using double precision operations 105 sec / 10 6 stars= 0.105 miliseconds per star Intel P4 [2.4 GHz]

32. The GAIA System Simulator June 2003RRFWG Meeting at Dresden - 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

33. The GAIA System Simulator June 2003RRFWG Meeting at Dresden Time ephemeris Chevychev 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.