DEM
Here we assume that the DEM file only includes the three-dimensional coordinates of points. The input format for the DEM is a three-column array, where the first column represents the x-coordinate, the second column represents the corresponding y-coordinate, and the third column is the z-coordinate.
The Digital Elevation Model (DEM) is a special 3D case. Typically, for landslide simulations, we obtain a DEM file composed of surface data, which consists of three-dimensional scatter points, with each x-y coordinate corresponding to a unique z value. Before generating the material points, we need to perform a simple processing step by rasterizing it on the x-y plane using inverse distance weighting (IDW). We then proceed to generate the material points based on our requirements.
DEM file pre-processing
The DEM file is a simple three-column array. Each DEM must be rasterized to ensure it is structured (regular) in the x-y plane.
MaterialPointGenerator.rasterizeDEM — MethodrasterizeDEM(dem, h; k=10, p=2, trimbounds=[0.0 0.0], dembounds=[0.0, 0.0])Description:
Rasterize the DEM file to generate particles. dem is a coordinates Array with three columns (x, y, z). h is the space of the cloud points in x and y directions, normally it is equal to the grid size in the MPM simulation. k is the number of nearest neighbors (10 by default), p is the power parameter (2 by default), trimbounds is the boundary of the particles, dembounds is the boundary of the DEM.
Through this function, we can rasterize the input DEM file and specify the spacing between each point (which is the same as the grid size in the MPM simulation). The trimbounds parameter is used to define the shape of the DEM file in the x-y plane; it is a two-dimensional array where each row represents a vertex of the shape in the x-y plane. The dembounds parameter can be used to specify the range of the DEM in the x-y plane; it is a vector that represents [xmin, xmax, ymin, ymax]. This can be utilized to process two DEMs of the same area at different times, ensuring they have completely consistent x-y coordinates.
DEM with a flat bottom surface
Suppose we have a DEM and we want to close it with a base plane, for example, at z=0.
MaterialPointGenerator.dem2particle — Methoddem2particle(dem, h, bottom)Description:
Generate particles from a given DEM file. dem is a coordinates Array with three columns (x, y, z). h is the space of particles in z direction, normally it is equal to the grid size in the MPM simulation. bottom is a value, which means the plane z = bottom.
DEM with a given bottom surface
If the base used to close DEM-1 is not a flat surface, we can designate another DEM-2 to serve as the base for closing DEM-1.
MaterialPointGenerator.dem2particle — Methoddem2particle(dem, h, bottom)Description:
Generate particles from a given DEM file and a bottom surface file. dem is a coordinates Array with three columns (x, y, z), which has to be initialized with the struct DEMSurface. bottom::DEMSurface should have the same x and y coordinates as the DEM, and the z value should be lower than the dem. h is the space of grid size in z direction used in the MPM simulation.
DEM-2 and DEM-1 should have exactly the same coordinates in the x-y plane. This can be achieved using rasterizeDEM.