December 5, 2023
The Elevation Grid Creation tool in Global Mapper uses any 3D vector data to create a gridded raster elevation layer. One type of elevation grid is a Digital Terrain Model (DTM), which represents the elevations in the earth’s surface, omitting any structures or vegetation. In Global Mapper, digital terrain models can be created, manipulated, used in analysis, and exported in one of the many supported elevation formats.
To create a DTM, first load your elevation data, open the Create Elevation Grid tool, choose your binning method, and click OK.
Digital Terrain Models
A digital terrain model (DTM) is a solid surface elevation layer that describes the terrain or ground on its own, omitting structures and features such as buildings and vegetation. This is similar to a digital surface model (DSM), which includes the structures and features on top of the ground. Both of these models can be created in Global Mapper Pro.
Tip: When creating a DTM from a point cloud, it’s a good idea to first classify the ground points using Global Mapper Pro’s classification tools. Available in the Point Cloud Analysis tool, the ground classification tool will automatically identify and label likely ground points within your data. When generating the elevation grid layer, filter by classification to exclude all points that don’t make up the ground surface.
Choose a Grid Creation Method
Multiple methods are available for interpolating vector data into a solid surface: TIN and the Binning methods. Choose the method that best suits the end use for this data.
Here is a visual comparison of these methods, shown using the Path Profile tool. This path shows three elevation grids generated from the same data using different methods. You can see that the binning method grid is smoother than the TIN surface. Both of these methods are commonly used, but Binnign is the most popular. People tend to take sides on which type is most accurate, but it depends on how accuracy is measured and how the data is used.
A Path Profile Comparing Generated Elevation Grids
The TIN Method
The first method Global Mapper offers for generating elevation grid layers is the Triangulated Irregular Network or TIN method. This is popular with users who want a surface that represents key points, or the most significant points, in the data. The key points, including the vertices of 3D line and area features, are connected 3D point features into a network of triangles. From there, the program interpolates over the triangular faces using the feature elevation and slope values to generate an elevation grid layer.
The Binning Method
The Pro version of Global Mapper includes variations on the binning method for generating an elevation grid. Binning is often considered to be better suited for point cloud processing as it doesn’t include every single point in the point cloud when generating the output grid. Points are chosen based on their elevation in the area. The Binning Minimum value chooses the lowest points in the area.
The binning method works by spatially binning the data into areas corresponding with the size of the output grid cells. One point value from each bin/grid cell is used to represent the cell in the final gridded layer. The elevation value from each bin that is used to generate the grid is determined by the specific binning method that is selected. For example, the Binning Minimum Value method uses the minimum elevation value from each bin to generate the grid.
Optional: Creating Flattened Areas in the DTM
Water bodies such as ponds, lakes, and rivers may not provide consistent point cloud data. When generating an elevation grid that contains water-covered areas, you may want to flatten those areas to a specified elevation value. This can be done by including a 3D area feature in the data used to create the grid and using the grid creation option to ‘Use 3D Area/Line Features as Breaklines’. This will burn the area feature’s elevation into the output grid, thus flattening the noise within the area. This can be used for road features, building footprints, or any other area features as well. To manually edit the grid after it’s been created, use the Terrain Painting tool.
With an elevation grid layer created to show the elevation as a surface, you can continue your analysis in Global Mapper to generate contour lines, generate watershed areas, perform volume calculations, or any other analysis function. To see more of what Global Mapper can do for you, visit the Tips & Tricks page.
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