基于WCS的FITS图像天球定位综述及通用可视化研究

Review on the Celestial Sphere Positioning of FITS Format Image Based on WCS and Research on General Visualization

求取FITS(Flexible Image Transport System)文件头中以键/值对形式记录的坐标参数是FITS图像在天球参考系中定位的关键,研究坐标参数求解的一般过程具有重要意义.通过结合观测相机相关参数、天文照相图片识别算法以及WCS(World Coordinate System)理论能够有效实现坐标参数的求解,其中,CCD参数可确定图像对应天区在星表中的坐标范围,从而与星表结合可构建区域星表;天文照相图片识别完成了图像与区域星表间的匹配,得到一定数量恒星的CCD平面坐标与其天球坐标的对应表;WCS根据球面到平面不同投影方式建立两个坐标系之间的传递函数,选择其中一种并代入对应表中数据,解算函数的转换参数从而确定图像像素及其对应的天球坐标.FITS图像作为天文领域科学数据传输与分析的主流数据格式,仅限于在专业天文软件中进行查看、编辑及分析,在天文科普教育中存在局限性.因此,研究一种通用的图像可视化方法意义非凡.通过对FITS与PNG或JPEG图像进行格式转换,以AVM(Astronomy Visualization Metadata)的形式将FITS文件头中的坐标参数转换为元数据并添加到PNG或JPEG的文件头中,能够满足天文爱好者在非天文软件平台下查看及分析天文图像的一般需求.整体设计流程通过java编程实现并通过SExtractor、虚拟天文台可视化工具WWT、图片查看器等软件进行了相关测试.

Calculating the coordinate parameters recorded in the form of key/value pairs in FITS （Flexible Image Transport System） header is the key to determine FITS images＇ position in the celestial system. As a result, it has great significance in research- ing the general process of calculating the coordinate parameters. By combining CCD related parameters of astronomical telescope （such as field, focal length, and celestial coordinates in optical axis, etc.）, astronomical images recognition algorithm, and WCS （World Coordinate System） theory, the parameters can be calculated effectively. CCD parameters determine the scope of star catalogue, so that they can be used to build a reference star catalogue by the corresponding celestial region of astronomical images; Star pattern recognition completes the matching between the astronomical image and reference star catalogue, and obtains a table with a certain number of stars between CCD plane coordinates and their celestial coordinates for comparison; According to d- ifferent projection of the sphere to the plane, WCS can build different transfer functions between these two coordinates, and the astronomical position of image pixels can be determined by the table＇s data we have worked before. FITS images are used to carry out scientific data transmission and analyze as a kind of mainstream data format, but only to be viewed, edited, and analyzed in the professional astronomy software. It decides the limitation of popular science education in astronomy. The realization of a general image visualization method is significant. FITS is converted to PNG or JPEG images firstly. The coordinate parameters in the FITS header are converted to metadata in the form of AVM （Astronomy Visualization Metadata）, and then the metadata is added to the PNG or JPEG header. This method can meet amateur astronomers＇ general needs of viewing and analyzing astronomical images in the non-astronomical software platform. The overall design flow is realized through the java program and tested by SExtractor, WorldWide Telescope, picture viewer, and other software.