Group of Atmospheric Optics, Universidad de Valladolid (GOA-UVa), Valladolid, Spain.
Departamento de Química y Física, Universidad de Almería, Almería, Spain.
PLoS One. 2022 Mar 31;17(3):e0265959. doi: 10.1371/journal.pone.0265959. eCollection 2022.
This paper presents the software application ORION (All-sky camera geOmetry calibRation from star positIONs). This software has been developed with the aim of providing geometrical calibration to all-sky cameras, i.e. assess which sky coordinates (zenith and azimuth angles) correspond to each camera pixel. It is useful to locate bodies over the celestial vault, like stars and planets, in the camera images. The user needs to feed ORION with a set of cloud-free sky images captured at night-time for obtaining the calibration matrices. ORION searches the position of various stars in the sky images. This search can be automatic or manual. The sky coordinates of the stars and the corresponding pixel positions in the camera images are used together to determine the calibration matrices. The calibration is based on three parameters: the pixel position of the sky zenith in the image; the shift angle of the azimuth viewed by the camera with respect to the real North; and the relationship between the sky zenith angle and the pixel radial distance regards to the sky zenith in the image. In addition, ORION includes other features to facilitate its use, such as the check of the accuracy of the calibration. An example of ORION application is shown, obtaining the calibration matrices for a set of images and studying the accuracy of the calibration to predict a star position. Accuracy is about 9.0 arcmin for the analyzed example using a camera with average resolution of 5.4 arcmin/pixel (about 1.7 pixels).
本文介绍了软件 ORION（基于星位的全天相机几何校准）。该软件的开发目的是为全天空相机提供几何校准，即评估每个相机像素对应的天空坐标（天顶角和方位角）。它有助于在相机图像中定位天体穹顶上的天体，如恒星和行星。用户需要为 ORION 提供一组在夜间拍摄的无云天空图像，以获取校准矩阵。ORION 会在天空图像中搜索各种恒星的位置。这种搜索可以是自动的，也可以是手动的。恒星的天空坐标和相机图像中相应的像素位置一起用于确定校准矩阵。校准基于三个参数：图像中天顶角的像素位置；相机相对于真实北方的方位角的偏移角度；以及天空天顶角和像素径向距离与图像中天顶角之间的关系。此外，ORION 还包括其他功能，以方便其使用，例如校准精度的检查。本文展示了 ORION 的一个应用示例，获取了一组图像的校准矩阵，并研究了校准的精度，以预测恒星的位置。在使用平均分辨率为 5.4 弧分/像素（约 1.7 像素）的相机进行分析的示例中，精度约为 9.0 角分。
