# Sino-InSpace: A Digital Simulation Platform for Virtual Space Environments
## 2 Platform Orientation and Data Source Analysis  
Compared to the majority of the digital earth and VGE platforms, Sino-InSpace focuses on visualization and analysis on a larger scale space including the construction of the virtual interplanetary space environment, digital planets, space environment/weather monitoring, space mission launch, space objects collision warning, landing area selection, and so on (Figure 1). Complete VGEs can be divided into four subtypes: the data environment, modeling environment, expression environment, and collaborative environment [8; 35; 40; 41]. The data environment is fundamental for the other three subtypes [42]. Therefore, the data source of VSEs is analyzed first and divided into two types: the environment element and the entity object element (Table 1). The environment elements are the basis for building the virtual space. In addition to the image, digital elevation model (DEM) and other basic geographic data, space activities also need to consider \begin{table}
\begin{tabular}{c c c} \hline \multicolumn{2}{c}{**Data Type**} & \multicolumn{1}{c}{**Content**} \\ \hline \multirow{4}{*}{Environment element} & Basic geographic environment & Remote sensing images on the surface of the planet, digital elevation model (DEM), and vector and feature data. \\ \cline{2-3}  & & The position, distribution, temperature and intensity information of physical space environment such as middle and upper atmosphere, geomagnetic field, ionosphere, radiant zone, and so on. The track and size information of space debris. \\ \hline \multirow{4}{*}{Entity element} & Background star & Astronomical catalogues of stars containing accurate position, proper motion, level, and color. \\ \cline{2-3}  & Planet in the solar system & The size, shape, texture, rotation speed, etc. of planets. \\ \cline{2-3}  & & Astronomical ephemerides used to calculate the position and velocity of planets. \\ \cline{2-3}  & & Object craft & Orbit elements, trajectories, attitudes, 3D models, and attributes of artificial satellites and spacecraft. \\ \cline{2-3}  & & The location, model, capability, and attribute data of all kinds of ground facilities such as optical telescopes, radar, launching and measurement, and control stations. \\ \hline \end{tabular}
\end{table} 
Table 1: Data source of virtual space environments. Figure 1: Platform orientation. the space environment such as the atmosphere, magnetic field, ionosphere, and space debris around the spacecraft during the flight. With all kinds of earth observation systems, we have accumulated considerable geographical environment data. For the Moon, Mars, asteroids, and other celestial bodies, we can also obtain rich remote sensing images and topographic data through detectors, and these data enhance the cognition of the planets. The data source of the space environment includes two types: (i) data collected by sensing instruments [43; 44] and (ii) data calculated by empirical models (e.g., NRLMSISE-00 empirical model [45], IGRF-12 model [46], and IRI2012 model [47]) developed using sensory data. With these data sources, datasets such as the position distribution, intensity, and density of various elements are achieved. Entity objects refer to the targets of direct or indirect participation in space activities, and related elements include the following types. (i) Background star. Sino-InSpace adopts the Tycho-2 catalogue [48] to calculate the current position, brightness, and size of stars, which are then described using the point-based rendering. (ii) Planet in the solar system. The data includes the radius, eccentricity, texture, rotation speed, etc. The speed and position are calculated by deploying the NASA Jet Propulsion Laboratory Development Ephemeris (JPL DE) 405 [49]. (iii) Spacecraft. As the main participants of space activities, the platform focuses on the expression of its position, posture, form, and attribute information. (iv) Ground facility.