Research On OpenGL Based 3D Visualization Of Digital Geological Logging

With the development of Geographic Information System (GIS) and 3D display techniques, expressing the realistic world by 3D model has become a hot spot in the field of surveying. The digital image based Geological Logging Information System, which is based on Photogrammetry, is a combination of close-range photogrammetry, digital image processing, and GIS space data management techniques and has achieved to extract geological logging data of hydroelectric project, integrate processing, managing, analyzing and result-outputting, which has upgraded specialty informatization and productivity level. Because of this, 3D visualization of engineering geological logging has become practical demands. Based on the fruits obtained by photogrammtric geological logging technique, this paper researches on 3D visualization technique of photogrammetric geological logging system for an excavated surface of a large hydroelectric project, which are as follows:(1) 3D modeling for excavated surface of hydroelectric project has been researched and realized. Based on the object features of photogrammetric geological logging and data management contents, various geological logging objects, including slope, foundation ditch and cave, are realized through OpenGL.(2) Based on traditional Mip Map pyramid texture mapping, this paper discusses to build a partition multi-resolution model for texture mapping to meet the need of large data size of digital geological logging system's exploded images. Researches prove that the partition multi-resolution model can overcome the shortcomings of Mip Map pyramid model which restrict image size and is more practical because it can meet the need for exploding image mapping in high resolution. Partition multi-resolution texture mapping helps to determine the image space information of the excavated face and refine the 3D display and pan speed of the logging scene through adjusting the map resolution with viewpoint dynamically.(3) Mapping of vector information on the surface of logging object is realized through ADO, which is a database access technique, according to the storage structure of the vector information of photogrammetric geological logging system. Moreover, the interpolation algorithm for discrete points on different surfaces in the linear vector mapping of cave model is discussed.(4) Under the man-machine interactive condition, 3D query and space measure of the logging objects and attribution query of the logging vector fruits are studied through the selective and feedback functions of OpenGL.(5) Based on the features of 3D model and the data of digital geological logging, an analogue plane is built on the excavated surface model according to a linear trace and the space attitude of bed is determined auxiliary by the stereo images of the slope. Results of experiments using real data prove that this method is practical for structural plane attitude measurement when there are only linear traces or only small bedding planes.