| The microtopography of loess cultivated slope is an important place for surface runoff and soil erosion process,and its high precision 3D surface model is an important data basis for further understanding and explaining the mechanism of soil erosion.In this paper,a kind of artificial tilt photogrammetry(ATP)is proposed to solve the problem that the 3D model obtained by the existing micro-terrain contact and non-contact measurement technologies can not fully and truly reflect the details of the surface micro-terrain.In ATP method,the microtopographic images of loess slope surface are obtained from vertical and other angles by hand-held digital camera,and using these images to construct the high precision model.The appearance and accuracy of the model are evaluated,and whether this method can fully express the real texture structure of the micro-terrain is evaluated,and whether this method is suitable for the construction of the 3D model of the loess slope surface is concluded.Then,on the basis of the application,the three factors of the photographing process of ATP method are studied one by one,and the influence of each factor on the accuracy of the 3D model of the surface is deeply understood,so as to achieve the purpose of optimization of the method.It provides theoretical support for the further popularization and application of ATP method.In this paper,the digital camera Nikon D90,was adopted by selecting three sizes of iron frames to lightly insert into the micro-surface(the highest position of soil surface protruding does not exceed the top edge of the iron frame).The surface images are collected from 1.2 m away from the loess slope and the surface micro-terrain model is obtained after aerial triangulation.Then lay 0.2 mm PE film on the surface and filling the surface with water to calculate the amount of microtopographical filling in order to determine the height error of the microterrain model.The results show that the plane error of the 3D model is ±1.9 mm,elevation error is ±2.6 mm.The accuracy of microterrain model is required and the texture of the model is clearly in line with the real surface texture structure,which will be beneficial to the data recording of soil erosion process and provide reliable data for further study of soil erosion mechanism in microterrain.In order to further study the applicability of ATP method and optimize the method,selecte three different resolutions cameras of high(24.3 million pixels),medium(12.3 million pixels)and low(6 million pixels),at a height of 1.5 m,1.0 m and 0.5 m above the surface,with the " " and "O" path respectively to obtain the surface images,then 18 groups of 3D surface models are established,and the correlation and accuracy are evaluated.The results show that the accuracy of the surface microterrain model is related to camera resolution,photographing height and photographing path: the higher resolution of the camera,the higher model accuracy;the higher photographing height,the lower model accuracy;The model generated by the " " path is better than the "O" path.The difference of the accuracy of each direction between the 18 groups of micro terrain surface models is not more than ±3 mm,which indicates that although the above three factors will affect the accuracy of the model,it does not change much.Therefore,the ATP method is not harsh on the operation requirements,which is convenient to popularize.To sum up,the method of obtaining micro-terrain model of loess cultivated slope by ATP is completely suitable for the construction of high precision 3D surface model of micro-terrain,and the operation is simple and easy to popularize.It can provide a reference for the rapid construction of micro-scale surface or ground object model,and can provide good data support for highly quantitative study of micro-scale soil erosion mechanism and soil erosion prediction and prediction. |
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