Aerial Lidar

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This section may be used to read aerial LiDAR files (LAS or text-based files are accepted) in order to visualize the data or create surfaces or solids from the data. Information may be viewed quickly and powerful tools of simplification are available. Loaded points may be transferred to surfaces or building footprints can be extracted. The tools here are more adapted for aerial classified LiDAR. It brings out information from the point cloud but can’t modify them. For data manipulation, this must be done within a VisionLidar project.

Option	Description
Aerial LiDAR	Options to open a LAS file are simple: choose a file then click on “Open file” button. If a text file is chosen, then the different columns for specific information shall be specified. The “Preview” button open an independent viewer to show the point cloud.
Bounding box	The bounding box is a 3D limit within which the LiDAR points are located. If the fields are changed, when viewing and transferring points, only those within the new limit will be treated.
Classification	Table to show how many points are in each class. Options to view points by intensity, elevation or both, to draw and erase points in the main window and to manage the density treated are available. The checkbox at the beginning of the row will hide the entire class. The density bar will only affect the number of processed points, placing it in the middle will remove one point out of two.
Building footprint extraction	This tool extract the rooftop of buildings from the point cloud by analyzing the Building class. Distance and elevation separations values define the breaking points of adjacent rooftops. Regularization allows different options for angles made by the roofs. “Extract” will process the point cloud and the results will appear in the preview. From there results can be drawn in the main window, added to a surface or extracted as a DXF or CSV file.
Add points to surface	This function adds points to a surface with or without simplifications. If the surface already has an outline, only points within the outline will be imported. It is also possible to exclude points within closed breaklines in a surface. Those lines just need to be selected in the table below before clicking on “Add points”.
Simplify by grid	This simplification tool analyzes the point cloud with a planimetric grid. If within a tile, points respect the tolerances, only one point will be kept, else the tile will be divided in four and each sub tiles will be analysed. “Grid size” is the length of a tile “Elevation tolerance” is the maximum difference between the lowest and highest point in a tile. “Isolated points tolerance” is a value to discard to high points from the process. “Use plane” calculates the elevation from a mean plane instead of vertically. “No. times” is the number of time subdivision of tiles can be done before keeping only one point regardless of the tolerances.
Simplify by triangulation	This tool simplifies the point cloud by analysing its triangulation and discarding triangles that does not show enough variation in slope and elevation with their neighbors. If “Simplify by grid” was also chosen, the triangulation will be done afterward, which will greatly diminish process time. “Slope tolerance” is the minimum variation of a slope between triangles to be considered significant. “Elevation tolerance” is the minimum difference of elevation to be considered significant. Breaklines can also be extracted and simplified with an maximum deviation and variation.