Menu: Analyze / Ground
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The ground detection will identify the lowest points in a point cloud and classify them to the class 2, which is the ground class determined by the ASPRS.
A triangulated surface, representing the ground, may also be created with this detection. This option can be turned on or off. The minimum cell size determines the precision of the surface; a smaller tile size will generate a surface with smaller triangles. The smaller the cell size, the longer the software will take to run the detection.
Different settings are available for this function:
Slope tolerance (in degrees): Surface angle deviation tolerance accepted in a cell. A higher tolerance will allow rougher surfaces but may lead to more erroneous points in the surface.
Minimum cell size (in distance units): Minimal size of tiles used in this algorithm. This value determines the precision of the detection. The smaller the value, the more precise the ground will be, but the longer the process will take. The minimal size of the cell should be smaller than the size of a project cell, or else the size of the project cell will be used. The information about the project’s cell size can be found in the menu “File / Project info”.
Limit by radius (in distance units): Limits the zone to be processed around the starting point. This option is useful when trying the best combination of parameters in a project or for small areas which are distinct from the rest of the project.
Starting point: Point where the algorithm will begin its process. It can be manually set or picked in the point cloud with the “Pick” button. If “Limit by radius” is used, the detection will be centered around this point.
Classification: This option will mark detected points as belonging to the ground class – this is classification of the ground points. The “Elevation” value is the maximum distance from the detected surface that a point may have to be considered as a ground point.
Create surface: Generates a surface by using the lowest points. The minimum size of the triangles will depend on the minimum cell size and the surface created can be found in the explorer under the “Object” tab in the surfaces list.
Flatten outline: This option was added because for some point clouds the points at the extremities of the project had varying elevations. This was creating surfaces with large disparities at the extremities. This option will flatten the extremities and will create a flatter surface without affecting the significant points.