Research And Application Of 3D Geological Modeling Algorithm Based On Digital Geological Mapping Data

The digital geological mapping technology has been popularized and applied in the national regional geological survey work for nearly 20 years,and has formed rich data.Based on the existing digital geological survey and mapping data,the establishment of 3D geological models by means of computer technology and methods was of great significance for the auxiliary regional geological surveys,and provided “a priori models” for deep geological survey.For a long time,field geological modeling was difficult because of its scarce data,no drilling and other engineering data constraints,and the related research was less than 3D geological modeling of mines.The implicit modeling methods such as potential field method could not be popularized and applied because of unclear expression,so it was urgent to develop intuitionistic and WYSIWYG 3D geological modeling methods.Based on the data of digital geological mapping,a set of original 3D geological modeling solutions was proposed.The research idea of "Digital geological mapping data→Geological boundary model→Geological interface model →Geological body model" is formed.The related geological modeling algorithms,such as geological boundary modeling,geological interface modeling,geological body modeling and complex geological phenomenon modeling,were designed and realized by programming.And the methods were practiced in the geological mapping of Majiaoba area in Sichuan Province and Zhenqian area in Fujian Province.The data were organized in 3D geological modeling,including digital geological mapping data such as geological points,routes,attitudes,sections,topography and geophysics data such as aeromagnetism,gravity and magnetomagnetism.Due to the lack of deep data,the geophysics data was very important.As the distribution of geological data was irregular,the spatial delaunay triangulation was used to organize the discrete geological data,and an improved algorithm was proposed to effectively eliminate the degradation of triangulation.A method for modeling the geological boundary was proposed in accordance with the V-shaped rule in tectonic geology.The terrain judgment and angle comparison in the V-shaped rule were quantitatively represented,and the local geological boundary generation algorithm was realized according to the V-shaped rule,and the splicing of the local geological boundary was realized based on the shape-preserving Hermitian algorithm.The error analysis of shape-preserving Hermitian algorithm showed that the error of geological boundary was affected by the distance between geological points.The denser the geological points,the smaller the error,which was consistent with the understanding that the shape of stratum could be controlled by infill geological points in geological mapping.Two schemes of geological interface modeling were proposed,including the geological interface modeling method by attitudes control or by sections control.The geological interface modeling method by attitudes control,in view of the situation that the attitudes data has the characteristics of sparseness and large spacing and cannot be directly used for interpolation,proposed establishing the attitude buffer for interpolation and to extending the attitude to carry out Coons surface interpolation.Based on the modeling method of attitude buffer interpolation,point buffer areas are constructed at the geological points containing attitudes,virtual geological interface points are extracted from the point buffer,and the geological interface is obtained by means of spatial interpolation.The attitude buffer could not only increase the number of virtual geological interface points,but also reflected the inclined dip pattern of rock strata.However,the virtual geological interface points in the buffer were sparse and spaced,so not all interpolation algorithms could be applied.Through the comparison of different interpolation algorithms,it was concluded that the Biharmonic interpolation algorithm could make the surface with the maximum curvature,and the simulation effect of the geological interface was the best,and the influence of different buffer sizes in the modeling of the geological interface was discussed.The geological interface modeling method of Coons surface interpolation based on attitude extension was proposed to extend downward along the dip direction of attitude,to simulate the four boundary lines required by Coons surface interpolation,and to obtain the geological interface by Coons surface interpolation.In contrast to the geological modeling methods,the geological modeling method based on the attitude buffer interpolation was more scientific,but more limited.The geological interface modeling method based on the Coons surface interpolation based on the extension of the attitudes has less restrictive conditions,but the Coons boundary lines needed to be inferred.Sections data was important for three-dimensional geological modeling.There were a large number of sections data interpreted by experts or geophysical data in geological mapping.The geological interface modeling method controlled by the sections took the surface geological boundaries and the section strata boundaries as the three-dimensional outline lines of the geological interface,and took the spatial points set after the dispersion of the three-dimensional outline lines as the sample data,and obtained the geological interface model of the simulated area by interpolation the sample data,and proposed different solutions especially for the flat or steep geological interface.The Biharmonic interpolation algorithm had a good effect on the construction of the gentle geological interface,while the Clough-Tocher interpolation algorithm had a better effect on the steep geological interface.A solution is proposed for the 3D geological modeling of complex geological phenomena such as folds and faults.The focus of modeling complex geological phenomena such as folds and faults is to solve the modeling of fold surfaces and fault surfaces.In the geological interface modeling,the paper proposes a fold modeling method based on the occurrence-extended Coons surface interpolation based on the geological interface modeling method by attitudes controll in view of the characteristics of the fold surface such as large curvature and complex deformation.Aiming at the problem of 3D geological modeling of faults,a block modeling method on both sides of the fault is proposed.The fault boundary lines were extracted from the surfaces and sections,interpolated to establish the fault plane model,and then extended from the fault plane to both sides of the section to extract the rock boundary line,and the Coons surface algorithm was used to establish the rock layer interface on both sides of the fault.The method of 3D geological body modeling were proposed.Firstly,the spatial triangulation models of geological interface,top surface,bottom surface and so on were established respectively,and then the intersection lines of each surface were obtained and the reserved parts were determined by intersecting treatment.Finally,the geological interfaces,top surface,bottom surface and sides were sutured into geological bodies by using the intersecting line as the suture line.The intersection algorithm between geological interface and terrain,the intersection algorithm between geological interface were designed and implementated.The three-dimensional geological model could be used in internal morphological simulation and lithologic pattern filling.The internal shape simulation was based on the reference of "potential" in foreign literature,and the isopotential line and isopotential surface were constructed in the geological model to simulate the internal changes of rock strata.The two-dimensional and threedimensional filling algorithm of the lithological symbol was designed.Finally,the method of the above geological modeling was applied in the geological mapping of the geological mapping of the Majiaoba area in Sichuan and Zhenqian area in Fujian.The geological boundary model was building by the attitude data.The deep indication of the the magnetotelluric(AMT)data was comprehensively considered,and five control sections were interpreted by the expert.The geological interface modeling was completed by the boundary line of the surface and the formation on the control section.The geological body model was constructed by combining the geological interface,the top,the bottom and the sides.The modeling research was carried out in particular for the fault and the fold.The cross section of the control crater was used in the geological mapping of the crater in Zhenqian area of Fujian and different methods were used to establish the geological interface and the geological body model of the crater.