The Design Of Survey Strategy System And Optimization Of Fiber Allocation Algorithm

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) as one of the National Mega-Science Programs is undertaken by the Chinese Academy of Science. The project, proposed by Chinese astronomers headed by Wang Shouguan and Su Dingqiang at the end of last century for the purpose of larget sample spectroscopic sky survey, is approved in April 1997, started in August 2001 and completed in August 2008. After the national final acceptance in June 2009, the telescope is titled as Guoshoujing Telescope on April 17, 2010, to commemorate the famous Chinese astronomer Guo Shoujing. The combination of a large clear aperture and wide field of view makes LAMOST the most important survey telescope in the world after SDSS and 2df. LAMOST will bring Chinese astronomy to a leading position in the large scale observations of optical spectra, and in the research field of wide field astronomy.The scientitic mission of LAMOST is large sample spectroscopic sky survey. Currently large sampe astronomy has become one of the most important research directions. It becomes more and more clear that some of the important and complex research topics, like cosmos structure, galaxy formation nd evolution, formation and evolution of the Milk Way system, et al., always need large sample statistic features. The technology development in the end of last century brings the possibility of the large sample survey. Further more, multi-wave band survey, including optical light, radio waves, infrared rays, X rays and gamma rays, can provide informations on several aspects. However the amount of celestial bodies in the sky is inestimable, and among all the currently known tens of billions of objects, only one ten-thousandth have their spectra. Thus the large sample spectroscopic sky survey comes to be the most primary work at present.The scientific goal of LAMOST focuses on extragalactic astronomy, structure and evolution of The Galaxy and multi-waveband identification. The spectroscopic survey carried by LAMOST will obtain more than tens of millions of spectra and will make contributions to the wide research astronomy. About 4000 targets are observed for each observation and more than tens of thousands of targets will be observed for one night. Obviously an automatic system is needed to help planning the observation process. The task of Survey Strategy System (SSS) of LAMOST is to deal with various subjective and objective restrictions, make completely covering on the survey sky, find the most valuable tile, allocate targets to fiber units, generate observation projects, ensure a high survey efficiency, save valuable astronomical observation time and produce as much as possible scientific products in accordance with the scientific requirements.The work of this paper is based on the previous mini-system and aims to serve the survey mode of full LAMOST system. By using the Domain Drive Design pattern, the relevant environment of the full system is analysied and the software structure is upgraded. The product generating flow is updated while the tiling and fiber allocating algorithms are optimized according to the concrete hardware features. By closely contacting the astronomical researchers, the software is promoted as a common astronomical sofeware and tested in the commissioning observation.The major function of SSS is the sky tiling and fiber allocation algorithm. On the basis of original algorithm, new tiling methods are designed and realized to solve the insufficient point, increase speed, serve the focal plane characteristics and find bright star centered tiles. Improved fiber allocation methods are also developed to raise the allocation ratio, avoid fiber collision and satisfy more complex user priority demands.The foundation of SSS is the observation targets. In this paper, a full featured distributed survey catalog software environment is developed, ensuring the ability of selecting targets, drawing up observation policy, managing the catalog, filtering targets and feedback observation.For the purpose of verifying the real software function and estimating the survey ability of the telescope, a group of real observation time based large sky area survey simulations are carried out, using the catalog from SDSS dr6. Simulation results have proved the validity of SSS and made meaning full assessment about the telecope.At last, we discuss the development of SSS.The creative of this article is:1) Upgration of the software sturctue using the Domain Drive Design pattern. The expansibility, robustness and usability are promoted. Besides, a virtual sky platform is developed with the ablity of showing the position and motion for celestial bodies and providing ocular help for making observation plans. A complete survey oriented software system is developed and is already used in telescope observation.2) Algorithm optimization. The tiling algorithm framework is refactored and a set of new concrete methods are realized, including Density-Lib, Quick-Shift, Boundary-Arise and SH tiling methods; A new fiber allocation algorithm is also developed, supporting priority handling, collision avoidance, group allocation and target reusing.3) Development of the star catalog manager environment. A common database accessing and catalog transfer utility is developed to help select targets; a new object filter module is designed and realized to deal with various observation restrictions; the survey observation project database is created together with its relevant supporting tools.