## 1 Introduction  
The traditional work mode of geological investigation in hydraulic engineering suffers from laborious data collection, subjective field analysis methods, and ineffective data management. Although there are many digital tools (such as MineScape [1] and FieldMove [2]) for geological engineering, they are not specifically developed for hydraulic engineering, which mainly focuses on the stability of multi-scale rock mass. As a result, in many cases, hydraulic engineers would rather document geological information manually. There has been a rapid development in digital measuring techniques, especially with geographic information system (GIS), global positioning system (GPS), and remote sensing (RS) techniques. With the increasing popularity of GPS, the technique has been widely used in geology. The intelligent electromagnetic compass (IEMC) has also been used in geology, transformed from military and aerospace applications. Tablets have also been developed with fast processing speeds. However, the techniques are not typically integrated, and there is no unified database. Thus, it is necessary to develop a system integrated with GIS, GPS, and RS embedded in a mobile device as this will help improve efficiency and reduce labor and time costs. The storage, access, and visualization of geological information has been studied for a long time. The interaction and accessibility of geology data are crucial. It is also studied for spatial data visualization, analysis, and exploration by integrating GIS, virtual reality (VR) and the internet [3]. Cooperation among the geo-information sciences, computer science, and mathematics is increasingly popular. [PERSON] et al. [4] established a data model that can be applied to any GIS system and summarized the basic rules to building the model. [PERSON] et al. [5] studied the management of different types of geological data in a database management system. The further development of GIS benefits significantly from good management of different data types, and optimized data structure and software architecture keep systems in good working condition. Multidimensional geology information can be described by geometric algebra [6]. However, it is also useful to analyze 2D geological pictures and draw geological boundaries using traditional methods. In MapIT [7], boundaries can be drawn, and profiles can be added onto 2D geological images. [PERSON] et al. [8] developed the Corel Geological Drafting Kit (CGDK) with visual basic for applications (VBA) for geological mapping, including stereographic projections and rose diagrams. It is a powerful tool that uses 2D geological pictures for geological field surveys. However, in reality, geological information exists in three dimensions. The integration of original geological data and the reconstruction of their 3D model will help engineers make decisions and avoid risks. The presentation of 3D geological information has been well studied. [PERSON] et al. [9] built a 3D model in a complex geological condition based on non-uniform rational B-spline (NURBS) technique and the triangulated irregular network (TIN) method. It was also applied for stability analysis of key surface blocks of rock slope [10] and identification of complex rock blocks in a tunnel [11]. [PERSON] et al. [12] presented a direct-georeferencing system combining hardware and software to obtain a high-precision position of images taken with an unmanned aerial vehicle (UAV), with which a more accurate 3D model can be established. The UAV and terrestrial laser scanning techniques can be integrated to build refined 3D models [13]. The 3D geological information was also loaded into a system. [PERSON] et al. [14] developed a 3D geological multi-body modeling system called GSIS, in which complex faults and multi-body 3D models were constructed based on cross-sections. [PERSON] et al. [15] developed a 3D geomorphological survey and mapping tool called GSTOP, in which real-time location, drawing boundaries, and geological profiles were realized in a 3D model. [PERSON] et al.