First, the Mathematica algebraic system is utilized to derive the forward formula of the gradient for rectangular prisms and complete the forward calculation of the gradient tensor. Second, the forward calculation of the gradient tensor is carried out for a complex density body composed of multiple prism units. Finally, with the rich visual output and display capabilities of Mathematica, a visualization system is established for the gravity gradient calculation of typical geological models such as prisms, spheres, and inclined steps.

The constructed visualization system can simulate the gravity gradient response results of density bodies under different physical property parameters and provide real-time dynamic visualization display, effectively presenting the characteristics and distribution laws of the gravity gradient of the field source.

The full tensor gravity gradient visualization system constructed based on Mathematica will provide a new means of interpretation for gravity gradient exploration data interpretation, and provide a basic platform for research workers to engage in research, scientific and technological thesis writing, and subject reporting.

First, we clearly define the connotation of gravity-aided navigation technology as the general term for two types of the aided navigation technologies: gravity compensation and gravity correction. Second, we analyze and review the development strategies, planning layout, development ideas, research and development paths, innovation results, test applications and some development trends worthy of attention in this research field in the United States and Russia, summarize the technical characteristics and successful experiences at diffe-rent stages of the research and development process of the two countries.

The characteristics of technological development in the United States include: (1) The demand for gravity compensation has been leading the development of gravity data modelling technology. (2) The demand for gravity compensation has been leading the development of gravity equipment technology. (3) The progress of gravity equipment technology has been promoting the development of gravity correction technology. The technological development characteristics in Russia include: (1) The military requirement has been dominating the development of sea and air gravity equipment technology. (2) The special attention has been paid to the researches on the correction algorithms of inertial navigation system parameter using gravity information. Finally, we compa-ratively analyze the differences and gaps research process between China and the two countries, and put forward five aspects of countermeasure and suggestion based on China's national conditions, involving directional issues such as research ideas, development focus, and priority arrangements.

The purpose is to attract ideas, exchange in-depth, reach consensus, and provide reference for decision-making departments to deploy the next work. Our specific countermeasures and suggestions are: (1) Give priority to the first task of gravity compensation. (2) Urgently promote detail gravity measurements in the key sea areas and gravimeter development for polar region. (3) Focus on the development of nonlinear filtering technology and filtering algorithms for gravity correction. (4) Give priority to the development of practical software-based gravity-aided inertial navigation systems. (5) Strengthen the requirement demonstration and top-level design for gravity-aided inertial navigation.

The Earth ellipsoid or sphere is redefined from the perspective of Riemannian manifold and the non-Euclidean geometric characteristics, and the topological relationship with plane and the influence on map projection are analyzed.

Based on the principle of manifold mapping, this paper considers that the basic contradiction of map projection (i.e. the contradiction between the earth surface and the map plane) should include two aspects, namely, un-developability and un-homeomorphism, which have impacts on distortions, domains and singular points of map projection, etc. Meanwhile, the correctness and feasibility of the authors' assertions about the principle of manifold mapping are further verified in the definition and the necessary and sufficient conditions of conformal map, etc.

This work expands the research idea for studying map projection from the perspective of Riemannian manifold mapping.

This paper proposes a two-level localization method including rough localization and accurate localization, which is based on 3D real map and applied to large indoor scenes such as shopping mall. To reduce the location computing time, this paper proposes a method to limit the scope of image database. Wi-Fi fingerprint matching algorithm is used to obtain the location results, and then limit the image database. In order to improve the positioning accuracy, a new method of constructing database is proposed. The whole scene is divided into multiple regions, and each region completes the database establishment independently and splices different databases. In order to reduce the location error, a scene recognition method is proposed. Deep learning method is used to remove the ceiling images and reduce the matching errors of feature points.

By comparing the location computing time before and after limiting the scope of image database, the proposed method improves the positioning precision from 1.89 m to 0.45 m, and reduces the positioning time from 6.113 s to 0.827 s per image.

The proposed method achieves sub-meter accuracy of indoor vision global positioning, while the feature points matching errors affect the positioning precision. In the future work, feature lines will be used to improve the positioning accuracy.

To solve the problem, this paper classified the direction relationships between object groups into three categories in the light of different visual cognitive outcomes of object groups; and it was found that the adjacent regions between object groups can reflect the impacts of distribution shapes of object groups and distribution density of their sub-objects on direction relationships. Based on this, a model for quantitatively calculating and qualitatively describing direction relationships between object groups was proposed. First, Delaunay triangulation is used to construct the adjacent region between object groups; then, different types of direction relationships are distinguished by preprocessing the triangles in the adjacent region; after that, the quantitative direction relationships between object groups are separated into the ones between the vertices and the edges of the triangles (i.e. the local quantitative direction relationships) for calculation. Finally, local quantitative direction relationships are transformed and integrated into the qualitative direction relationships between object groups.

Experimental results show that:(1) The proposed model can reasonably classify the direction relationships between object groups, and accurately distinguish and describe the direction relationships in some complex situations. (2) It can fully consider the impacts of distribution shapes of object groups and distribution density of their sub-objects on direction relationships, and effectively determine the direction relationships between different geometric types of object groups in map space.

The proposed model has good applicability and feasibility, which can overcome the disadvantages of existing models, and improve the accuracy of determining the direction relationships between object groups.

First, the one-way Doppler observation model and observation partial derivative are deduced theoretically, and the main error sources affecting the accuracy are analyzed. Then, the frequency deviation is estimated and the USO long-term drift prediction model is constructed during the execution of Tianwen-1 precise orbit determination using the one-way Doppler measurements. Finally, the accuracy of frequency bias resolution is analyzed theoretically based on its key factors.

The USO drift rate is 0.075 75±0.006 20 Hz/d.

This paper provides a feasible frequency drift calibration method for space-borne USO, and it constructs a priori frequency model for space-borne USO of Tianwen-1.

We investigate the dynamic precise baseline solution method and the inter-satellite double-difference ambiguity fixing method of low-orbit formation satellite, and analyze the contribution of BDS-3 (B1C, B2a) and GPS (L1, L2) observation of LT-1 A/B in precise baseline determination.

The results show that compared with GPS, the residuals of B1C and B2a observations of BDS-3 are significantly smaller, suggesting a higher signal accuracy.The baseline overlap accuracies of GPS-based, BDS-based, and GPS/BDS combined solutions are 0.8 mm, 0.6 mm, and 0.5 mm, respectively. The BDS-based baseline accuracy is 25% higher than that of GPS, and the GPS/BDS combined solution can further improve the baseline accuracy by 37.5% and 16.7% relative to the GPS- and BDS-baselines.The baseline difference between the GPS-based and BDS-based baseline solutions is 1 mm in 3 dimensional directions.

The analysis suggests that the single BDS-3 system can achieve precise baseline determination for low-orbit formation satellites at the 1 mm level and combined GPS/BDS solution will further improve the accuracy than single-system solution.

The interferometric point target analysis (IPTA) method was used to perform InSAR deformation time-series analysis on the Xieliupo landslide. The artificial corner reflector (CR) and global navigation satellite system (GNSS) were installed at the same location of the landslide, and the position of GNSS ground equipment was identified and confirmed by the CR on LT-1 data. The observation results of GNSS were used to verify the accuracy of InSAR results.

The annual cumulative maximum deformation of the landslide body exceeds 3.4 m. The accuracy of InSAR deformation time-series obtained from LT-1 satellites reaches 7.5 mm in line of sight. The maximum deformation rates of the tail, middle, and foreside of the landslide exceed 25 mm/d, 11 mm/d, and 2 mm/d, respectively, which indicates the landslide is in the stage from slow sliding to very slow sliding.

Through the comprehensive analysis of imaging mode, repeated observation interval, coherence change, baseline control range, and deformation detection ability, it can be found that the comprehensive efficiency of LT-1 satellite has reached the design indicators, and LT-1 satellite has good ability in regularized wide area surface deformation and monitoring. The high-frequency, strict regression, and consistent observation mode of LT-1 will play an important role in geological hazards identifying and monitoring on large-scale.

Taking the examples of the 2022 Luding earthquake in Sichuan Province,China, the 2023 Turkey earthquake, and the Jishishan earthquake in Gansu Province, China, coseismic deformation monitoring will be conducted. The deformation maps will be assessed in terms of accuracy and monitoring capabilities. Additionally, emergency assessments of secondary earthquake hazards and remote sensing investigations of active fault zones will be carried out based on the high-resolution SAR data from the LT-1 satellite.

By comparing the co-seismic deformation results derived from LT-1 satellites with the results from concurrent other SAR satellites and global navigation satellite system (GNSS) measurements, it has been verified that the LT-1 satellite has significant advantages in terms of monitoring accuracy and spatiotemporal resolution. In addition, leveraging the high-resolution advantage of LT-1 SAR satellite imagery, it is possible to quickly obtain information on the distribution of earthquake-induced landslides and accurately delineate the accessibility of roads in the affected area. This capability effectively supports earthquake emergency response and disaster assessment efforts. Furthermore, thanks to the L-band sensor, the LT-1 satellite exhibits strong penetration capabilities, thus enabling the detection of hidden faults.

Through multiple case studies in the seismic industry, encompassing various areas such as coseismic deformation monitoring, emergency response, and hidden fault detection, the results have demonstrated that the LT-1 satellite constellation has a significant breadth and depth of applications in the seismic industry. In the future, it will effectively support scientific research on seismic cycles and earthquake emergency operations.

This paper proposes a knowledge-guided three-dimensional visualization method of spatiotemporal narrative of bridge construction process. First, we construct a bridge construction knowledge map with “object-behavior-state” three-domain association by analyzing the bridge construction process, then break through the key technologies of narrative element analysis and matching, 3D scene mapping and instantiation, and 3D dynamic visualization of spatiotemporal narrative. Finally, we develop a prototype system and carries out case study experimental analysis.

The results show that the correct rate of answering questions in the experimental group reaches 76.5%, which is 13.2% higher than that of the control group; under the comprehensive perspective of clarity, richness and comprehension difficulty, 78.8% of the personnel in the experimental group have good cognitive experience, which is 45.5% higher than that of the control group.

By accurately describing the bridge construction objects, features and interrelationships, the unified expre-ssion and association management of bridge construction knowledge map is realized, and based on this, the three-dimensional dynamic visualization expression of the bridge construction process is carried out by using spatiotemporal narratives, which effectively enhances the education level of bridge construction process cognition with the help of interactivity and immersion of three-dimensional scenes.

Quasi-4-dimensional ionospheric modeling is introduced into regional ionospheric delay modeling in China and four schemes of 50,100,150 and 200 reference stations uniformly distributed in China (day of year 201—207) are adopted for ionospheric modeling.

The results show that when the number of stations used in ionospheric modeling increases from 50 to 200, the accuracy of ionospheric model products increases from 2-3 TECU to better than 0.8 TECU. Compared with the current ionospheric-free combined PPP, the convergence time of BDS-3 dynamic PPP can be deceased by 77%. In addition, the convergence time of GPS+BDS-3 dynamic PPP is reduced from 13.51 min to 4.45 min.

High-precision ionospheric model products can significantly shorten the convergence time of PPP-B2b.