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LIDAR_EXTRACT

Marius Lazar
Updated

LIDAR_EXTRACT

The LIDAR_EXTRACT command allows for automatically extracting building outlines, tree points/outlines, and linear powerlines from classified Lidar point clouds. Building extraction requires classified building points, tree extraction requires classified high vegetation points, and powerline extraction requires classified powerline points. The following parameters are supported by the command:

  • FILENAME - filename or description of loaded Lidar layer(s) to extract from. This parameter can be listed more than once to specify multiple input files, like FILENAME="FILENAME_1" FILENAME="FILENAME_2".
  • GRID_BIN_SIZE - specifies how many native spacings in size to make each bin, or for building extraction this is the gating distance for the local neighborhood used in principal component analysis. For example a value of GRID_BIN_SIZE="3.0" would make each square bin/ neighborhood 3 times the calculated native spacing of the point data. The default is GRID_BIN_SIZE="0.5" which queries the data at half of the native spacing. If you want to specify a spacing in meters rather than as a multiple of the native spacing for the point cloud, use a negative value. For example, to get a spacing of 0.6 meters, use GRID_BIN_SIZE="-0.6".
  • TYPE - specifies what type of features to extract. If you don't provide a TYPE parameter all types will be extracted. The following values are valid:
    • ALL - extract all types
    • BUILDING - extract building/ roof outlines. Note you must already have classified building points for the building extraction to work.
    • TREE - extract tree points/ outlines. Note you must already have classified high vegetation points for the tree extraction to work.
    • POWERLINE - extract powerline features. Note you must already have classified powerline points for the line extraction to work.

Building Extraction Options

Use for TYPE=BUILDING.

  • LIDAR_PLANE_MAX_OFFSET - specifies the maximum RMSE (root mean square error) in meters from a best-fit local plane that the points in a small region all have to be within in order to consider the region a potential planar (building) region. The default is LIDAR_PLANE_MAX_OFFSET=0.08 (8 cm). If you have lower resolution data you might need to bump this up a bit. A good value should be at least a couple of times the absolute error in elevation for the data set.
  • LIDAR_CREATE_FOOTPRINTS - This is used to create polygons representing ground footprints of buildings. If LIDAR_CREATE_FOOTPRINTS=YES, the following can be specified: 
    • LIDAR_SIMPLIFY_FOOTPRINT - enable to simplify buildings by removing extra vertices that do not move the original boundary further than the specified LIDAR_SIMPLIFICATION_EPSILON value. Cannot enable both LIDAR_REGULARIZE_FOOTPRINTS and LIDAR_SIMPLIFY_FOOTPRINTS.
    • LIDAR_SIMPLIFICATION_EPSILON - If LIDAR_SIMPLIFY_FOOTPRINT=YES, specify the line simplification parameter given in meters used in Douglas-Peucker line simplification of footprint boundaries.
    • LIDAR_REGULARIZE_FOOTPRINTS - enable to regularize building footprints so that corners become 90 degrees and opposite walls are parallel. Cannot enable both LIDAR_REGULARIZE_FOOTPRINTS and LIDAR_SIMPLIFY_FOOTPRINTS.
    • LIDAR_MIN_FOOTPRINT_AREA_SQM - Minimum footprint area required for extraction methods to proceed with simplified building model construction.
    • LIDAR_FOOTPRINT_HEIGHT - specify the elevation in meters for all generated building footprints features.
  • LIDAR_CREATE_SIDEWALLS - Add side walls to simplified building models by connecting footprints to identified planes.
  • LIDAR_CREATE_SEPERATE_ROOF_PLANES - Create simplified planes representing planar segments.
  • LIDAR_CREATE_BUILDINGS_AS_MESH - Create triangular mesh for each building from building points by way of a restricted delaunay triangulation.
    • LIDAR_COLOR_VERTICES - Color vertices in building mesh by Lidar intensity.
    • LIDAR_IS_MESH_RECONSTRUCTED - Enable with LIDAR_IS_MESH_RECONSTRUCTED=YES to use only a percentage of the building points to generate the mesh features, resulting in less complicated meshes.
    • LIDAR_RECONSTRUCTION_RATE - If LIDAR_IS_MESH_RECONSTRUCTED=YES, set the percentage of the building points to generate the mesh.
  • LIDAR_PSEUDOMEASUREMENTS_AT_PLANAR_INTERSECTIONS - Sharpen edges and stitch planes by adding points at planar intersections.
  • LIDAR_PLANE_MAX_ANGLE - Specify the maximum angle (in degrees) between adjacent best-fit planes such that they can still be considered part of the same plane when identifying flat building surfaces.
  • LIDAR_MIN_POINTS_IN_PLANE - Minimum number of points required (by RANSAC) to identify a planar segment.
  • LIDAR_MAX_DISTANCE_TO_PLANE - Maximum distance from a plane required (by RANSAC) to associate a point to a planar segment.
  • LIDAR_MAX_ITERATIONS - specify how many plane models will be tested in the analysis.
  • LIDAR_NORMAL_WEIGHT - specify how important the point normal vectors are in matching the points against a plane model.

Tree Extraction Options

Use for TYPE=TREE.

  • CREATE_TREE_POLYS - specified that approximate tree outline polygons should be created. Add CREATE_TREE_POLYS=YES to enable.
  • LIDAR_MIN_HEIGHT - specifies the minimum height above ground (in meters) for a tree crown point to create a point at the tree crown location.
  • LIDAR_TREE_MIN_SPREAD - specifies the minimum spread/width (in meters) which is the minimum width of a tree
  • LIDAR_TREE_MAX_SPREAD - specifies the maximum spread/width (in meters) which is the maximum width of a tree

Powerline Extraction Options

   Use for TYPE=POWERLINE.

  • POWERLINE_MAX_DIST_FROM_LINE - specifies the maximum distance (in meters) from the best-fit 3D line of points for a connected powerline segment that the points in a new candidate segment can be and still be connected.
  • POWERLINE_MAX_ANGLE_DELTA - specifies the maximum difference in angle (in degrees) from a straight line that the points in a new candidate segment can be and still be connected.
  • POWERLINE_MIN_LEN - specifies the minimum total length in meters that a connected powerline must be in order to be kept
  • POWERLINE_MAX_VERT_DIFF_PER_M - specifies the maximum difference in elevation allowed per meter to allow when connecting short segments to a longer continuous powerline. The default value is 0.5m, which allows for a change in elevation of 0.5m over a 1m distance between points. You might specify a slightly larger value if your data is noisy.
  • Specify Bounding Box for Operation

    See also Specify Bounds for Operation

    • GLOBAL_BOUNDS - specifies the combine bounds in units of the current global projection. There should be 4 values in a comma-delimited list following the parameter name. The values should be in order of minimum x, minimum y, maximum x, maximum y.
    • GLOBAL_BOUNDS_SIZE - specifies the combine bounds in units of the current global projection. There should be 4 values in a comma-delimited list following the parameter name. The values should be in order of minimum x, minimum y, width in x, width in y.
    • LAT_LON_BOUNDS - specifies the combine bounds in latitude/longitude degrees. There should be 4 values in a comma-delimited list following the parameter name. The values should be in order of west-most longitude, southern-most latitude, eastern-most longitude, northern-most latitude.
    • LAYER_BOUNDS - specifies that the operation should use the bounds of the loaded layer(s) with the given filename. For example, to export to the bounds of the file "c:\test.tif", you would use LAYER_BOUNDS="c:\test.tif". Keep in mind that the file must be currently loaded.
    • LAYER_BOUNDS_EXPAND - specifies that the operation should expand the used LAYER_BOUNDS bounding box by some amount. The amount to expand the bounding rectangle by should be specified in the current global projection. For example, if you have a UTM/meters projection active and want to expand the bounds retrieved from the LAYER_BOUNDS parameter by 100 meters on the left and right, and 50 meters on the top and bottom, you could use LAYER_BOUNDS_EXPAND="100.0,50.0". You can also specify a single value to apply to all 4 sides, or supply 4 separate values in the order left,top,right,bottom.
    • SNAP_BOUNDS_TO_MULTIPLE - specifies that the top-left corner of the bounding box for the operation should be snapped to a multiple of the given value. For example, using SNAP_BOUNDS_TO_MULTIPLE=1 will snap the top-left corner to the nearest whole number. The values will always go smaller for X/easting/longitude and larger to Y/northing/latitude so you always get at least what is requested.
    • SNAP_BOUNDS_TO_SPACING - specifies that the top-left corner of the bounding box for the operation should be snapped to a multiple of the resolution of the operation. For example, if you are exporting at 5 meter spacing, the top left corner will be snapped to the nearest multiple of 5. Use SNAP_BOUNDS_TO_SPACING=YES to enable or SNAP_BOUNDS_TO_SPACING=NO to disable. If not provided, the global setting for snapping exports to the nearest sample spacing boundary from the Advanced section of the General tab of the Configuration dialog will be used.
    • USE_EXACT_BOUNDS - specifies that the exact bounds that were defined in the command should be used. Generally, when the bounds specified in a command are not the same as the data bounds, the command uses the intersection between the two. When USE_EXACT_BOUNDS=YES is specified, the command will use the bounds as specified, instead of the intersection.
  • Lidar Advanced Filter Options

    See aso Lidar Advanced Filter Options

    • LIDAR_ELEV_RANGE - specifies the range of elevations to include in the grid in meters. By default all elevations are gridded, but if you want to restrict values to say 50m - 150m, you could add LIDAR_ELEV_RANGE="50,150".
    • LIDAR_HEIGHT_RANGE - specifies the range of heights above ground to keep in meters. By default all heights are used, but if you want to restrict values to say 0m - 2m above ground, you could add LIDAR_HEIGHT_RANGE="0,2".
    • LIDAR_SCAN_ANGLE_RANGE - specifies the range of scan angles to include in the grid in degrees. By default all scan angles are gridded, but if you want to restrict the grid to only those points with scan angles between 0 and 30 degrees, you could add LIDAR_SCAN_ANGLE_RANGE="0,30".
    • LIDAR_FILTER - specifies a comma-separated list of Lidar class numbers to export. Provide a minus sign to remove the type from the filter rather than add it. The filter starts off with nothing in it if you provide a LIDAR_FILTER string, but you can add ALL to enable everything or NONE to clear the filter, then add or remove stuff after that. For example, to specify a class filter with only types 2 and 3 enabled, use LIDAR_FILTER="NONE,2,3". To get one with everything but classes 2 and 3, use LIDAR_FILTER="ALL,-2,-3". If no LIDAR_FILTER is provided then all types currently enabled in the shared global Lidar filter are used.
    • LIDAR_RETURN_FILTER - specifies a comma-separated list of Lidar return types to enable or disable. Provide a minus sign to remove the type from the filter rather than add it. The filter starts off with the current filter settings, but you can add ALL to enable everything or NONE to clear the filter, then add or remove stuff after that. For example, to specify a return filter with only unknown and first returns, use LIDAR_RETURN_FILTER="NONE,0,1". To get one with everything but the first return, use LIDAR_RETURN_FILTER="ALL,-1". The numeric values have the following meanings:
      • 0 - Unknown Returns
      • 1 - First Return
      • 2 - Second Return
      • 3 - Last Return
      • 4 - Single Return
      • 5 - First of Many Returns
      • 6 - Second of Many Returns
      • 7 - Third of Many Returns
      • 8 - Last of Many Returns
    • LIDAR_COLOR_FILTER - specifies a color to include in the grid. If no value is provided then all colors are gridded. Otherwise, you can provide multiple LIDAR_COLOR_FILTER parameters of the format LIDAR_COLOR_FILTER="RGB(red,green,blue)" to specify colors to keep. The LIDAR_COLOR_DIST parameter specifies how far from an exact match to a specified color that a point color can be to be kept.
    • LIDAR_DENSITY_RANGE - specifies the range of point densities in points per square meter to include. Any Lidar points in regions with densities outside the range are ignored. If you use two values then everything between the values is used. If only one value is specified then all points in areas >= to the specified value are used. For example, LIDAR_DENSITY_RANGE="1.0" means that all points in areas with densities of 1.0 points per square meter or higher are used.
    • LIDAR_SOURCE_ID_LIST - specifies a comma-separated list of point source IDs to keep. If no list is provided all points are kept. For example, to keep just points with a source ID of 5 or 6, use LIDAR_SOURCE_ID_LIST="5,6".
    • LIDAR_INTENSITY_RANGE - filter to only the specified intensity values. The value is a pair of integers representing the range of intensity values to be included. Example: LIDAR_INTENSITY_RANGE=100,15. If only the first value is provided, it will be considered the minimum intensity value, so all values greater than that value will be included.

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