# GNSS-Assisted Visual Dynamic Localization Method in Unknown Environments
## 1 Introduction  
Existing satellite positioning and navigation systems such as GPS (Global Positioning System), GLONASS (Global Orbiting Navigation Satellite System), BDS (Beidou Navigation Satellite System), Galileo (Galileo Satellite Navigation System), QZSS (Japanese Quasi-Zenith Satellite Navigation System), and IRNSS (Indian Regional Satellite Navigation System), together with corresponding ground-based and satellite-based augmentation systems, comprise the infrastructure for global PNT (positioning, navigation, and timing) services [1, 2]. The development of satellite navigation and positioning systems have changed people's ways of life, the styles of battlefield perception, and the modes of traffic management, which has promoted the development of science and technology, economies, and societies. However, at the same time, satellite positioning and navigation systems havenatural vulnerabilities, such as weak signals, poor penetration abilities, and susceptibility to interference [3]. In some complex environments, such as urban canyons, tunnels, or battlefields with strong interference, GNSS (Global Navigation Satellite System) signals are weakened or even rejected, which causes the position information obtained by the GNSS receiver to be unavailable, and thus, it is necessary to rely on other navigation methods (e.g., Wi-Fi [4], UWB (ultra-wide band) [5], 3D LiDAR and vision [6], etc.) to obtain reliable global position coordinates. Visual navigation and localization comprise a passive and reliable localization model [7] that can realize autonomous navigation and localization in a location environment after acquiring video or image sequences, and visual navigation and localization have the advantages of possessing anti-interference abilities, being capable of high accuracy, and being low cost, and so they are widely used in the field of autonomous intelligence [8]. However, the state estimation positions obtained by visual localization are relative, it is difficult to determine the global position of a carrier, and there is a drift phenomenon in the long-term localization of a visual navigation error. Two navigation and localization methods, GNSS and vision, have their own advantages and disadvantages, and they can form complementary advantages [9; 10]. GNSS can inhibit the rapid accumulation of visual navigation errors, and visual navigation can achieve continuous navigation when GNSS is subjected to occlusion and interference, which improves the navigation and localization continuity and accuracy of GNSS. There are many experts and scholars that have conducted GNSS and visual navigation research. For example, in the literature, the authors of [11] utilized GNSS as an external absolute positioning system to provide scale information for monocular visual odometers, and this assisted the visual odometers used for navigation and positioning. There have been more studies on GNSS and vision for loose combinations of navigation and localization. [PERSON] and [PERSON] [12] firstly proposed a GNSS/VO loose combination system which used a cart equipped with a GNSS receiver and a binocular camera for experiments, and they confirmed that the performance of the GNSS/VO loose combination system was better than that of a pure visual VO system. [PERSON] et al. [13] investigated the performance of a binocular-vision-assisted GNSS for continuous navigation in harsh environments, and it loosely combined pure visual navigation results with GNSS results. The experiments showed that when the GNSS accuracy was reduced to 10 m in a weak GNSS environment, the accuracy of the visual navigation results was better than 1 m, and so the visual navigation system could well assist the GNSS for continuous navigation. In addition, [PERSON] et al. [14] used a tightly combined GNSS/inertial system which utilized pseudo-ranging or carrier-phase raw observations, and the final experiments proved that when the number of satellites was less than four, the tightly combined localization solution could still be carried out. [PERSON] et al.