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LIDAR_CLASSIFY

Marius Lazar
Updated

LIDAR_CLASSIFY

The LIDAR_CLASSIFY command allows for automatically identifying and classifying ground-shot or building/high vegetation points from Lidar point clouds. The following parameters are supported by the command:

  • FILENAME - filename or description of loaded layer(s) to classify Lidar points in. This parameter can be listed more than once to specify multiple input files, like FILENAME="FILENAME_1" FILENAME="FILENAME_2".
  • TYPE - specifies what type(s) of points to classify. If you don't provide a TYPE parameter only ground points will be classified. To classify multiple types, provide a comma-separated list, like TYPE="GROUND,NONGROUND,POWERLINE". The following values are valid:
    • GROUND - classify ground shot points.
    • NONGROUND - classify building/high vegetation points. Note you must already have classified ground points for the building/tree classification to work properly.
    • POLE - classify pole points.
    • POWERLINE - classify powerline vegetation points. Note you must already have classified ground points for the powerline classification to work properly.
    • NOISE - classify high and low noise points.
    • HIGH_NOISE - classify high noise points.
    • LOW_NOISE - classify low noise points.

Ground Point Classification Options

Use for TYPE=GROUND

  • GRID_BIN_SIZE - specifies how many native spacings in size to make each bin initially for the algorithm. For example a value of GRID_BIN_SIZE="3.0" would make each square bin 3 times the calculated native spacing of the point data. The default is GRID_BIN_SIZE="3.0" for classifying ground points and GRID_BIN_SIZE="1.0" for non-ground (building/tree) points. 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".
  • LIDAR_RESET_GROUND - specifies that any points that are already marked as ground should be reset to unclassified to start the process. Add LIDAR_RESET_GROUND=YES to reset the points.
  • LIDAR_CURVATURE - specifies the minimum height differential (curvature) in meters for the first pass of the MCC algorithm. The default is LIDAR_CURVATURE="0.3".
  • LIDAR_MAX_HEIGHT_DELTA - specifies the maximum height difference to consider as still possibly ground when removing points that are likely non-ground (i.e. buildings or vegetation) using a morphological filter before running the MCC algorithm to find ground points. You can provide a value of 0 to skip the morphological filter altogether and just run the MCC algorithm.
  • LIDAR_SLOPE - specifies the slope in degrees that is close to the expected steepest slope in the region being classified. This is used by the morphological filter which removes likely non-ground points before running the MCC algorithm to find ground points.
  • LIDAR_MAX_BUILDING_WIDTH - is a value specified in meters to help remove large building areas from the ground classification. This filter compares the local minimum to neighbors in progressively larger areas building to the specified maximum building width.

Non-Ground (Building/Tree) Point Classification Options

use for TYPE=NONGROUND.

  • GRID_BIN_SIZE - specifies how many native spacings in size to make each bin initially for the algorithm. For example a value of GRID_BIN_SIZE="3.0" would make each square bin 3 times the calculated native spacing of the point data. The default is GRID_BIN_SIZE="3.0" for classifying ground points and GRID_BIN_SIZE="1.0" for non-ground (building/tree) points. 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".
  • LIDAR_RESET_NON_GROUND - specifies that any points that are already marked as one of the types being classified should be reset to unclassified at the start of the operation. Add LIDAR_RESET_NONGROUND=YES to reset the points.
  • LIDAR_MIN_HEIGHT - specifies the minimum height above ground that a point has to be in order to consider it as a possible building or high vegetation point.
  • 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_PLANE_MAX_ANGLE - specifies 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_TREE_MAX_OFFSET - specifies the minimum 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 vegetative region. The default is LIDAR_TREE_MAX_OFFSET=0.15 (15 cm). If you have lower resolution data you might need to bump this up a bit. This value must be larger than the LIDAR_PLANE_MAX_OFFSET value.

Powerline Point Classification Options

use for TYPE=POWERLINE.

  • POWERLINE_BIN_SIZE - specifies the size of each bin (meters per edge) when evaluating points to see if they are clustered as needed for the powerline classification algorithm. Typically you will leave this at the default setting of 1 meter bins (i.e. POWERLINE_BIN_SIZE="1.0"). You might use slightly larger bins for data that is lower density (around 20 points / sq m), up to 2 meter bins.
  • LIDAR_RESET_NONGROUND - specifies that any points that are classified as a powerline-related type will be reset to unclassified at the start of the operation and that other already classified non-ground points will be considered as possible powerlines. Add LIDAR_RESET_NONGROUND=YES to reset the points.
  • LIDAR_MIN_POWERLINE_HEIGHT - specifies the minimum height above ground (in meters) that a point has to be in order to consider it as a possible powerline point.
  • POWERLINE_MAX_DIST_FROM_LINE - specifies the maximum distance (in meters) from the best-fit 3D line of points with similar elevations in a bin that any points can be and still be considered powerlines.
  • POWERLINE_MAX_VERT_DIFF_PER_M - specifies the maximum difference in elevation allowed per meter to consider points as possibly part of the same powerline segment. 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.

Pole Point Classification

  • POLE_SMOOTH_COUNT - how many times to smooth data.

  • POLE_MIN_NEIGHBOR_DIS - how far away to look for neighbor points.

  • POLE_MIN_LEN - how tall a potential point needs to be for it to be classified.

  • POLE_MIN_COUNT - how many points a potential pole needs to have for it to be classified.

  • POLE_MIN_THRESHOLD - percentage something is pole-like.

  • POLE_MAX_EXTENT - how far a potential pole can extend horizontally and still be classified as a pole.

Noise Point Classification Options

use for TYPE=NOISE.

  • NOISE_BIN_SIZE - specifies how many native spacings in size to make each bin initially for the noise classification algorithm. The noise classification algorithm identifies points that are far outside the normal range in a local area of the point cloud. This value will typically be large, like NOISE_BIN_SIZE=128, to consider local areas that are 128 times the nominal point spacing in each direction.
  • LIDAR_RESET_NOISE - specifies that any points that are already marked as noise should be reset to unclassified to start the process. Add LIDAR_RESET_NOISE=YES to reset the points.
  • LIDAR_RESET_CLASSIFIED - controls whether or not points that are already classified can be identified and marked as noise points. Add LIDAR_RESET_UNCLASSIFIED=NO to only check unclassified points for noise.
  • NOISE_STD_DEV - specifies how many standard deviations above or below the mean for an area that a point elevation needs to be in order to be considered noise. Default is NOISE_STD_DEV=3.0.
  • LIDAR_ELEV_RANGE - specifies that any points with elevations outside of a specified range should be marked as high or low noise. To specify a range of acceptable values in meters, specify the minimum allowed elevation followed by a comma and the maximum allowed elevation. For example, if you want to mark everything outside the range 50m - 150m as noise, you could add LIDAR_ELEV_RANGE="50,150".
  • LIDAR_HEIGHT_RANGE - specifies that any points with height above ground outside of a specified range should be marked as high or low noise. To specify a range of acceptable values in meters, specify the minimum allowed height followed by a comma and the maximum allowed height. For example, if you want to mark everything more than 2 meters below the ground surface as low noise and everything more than 500m above the ground surface as high noise, use LIDAR_HEIGHT_RANGE="-2,500". The default value is LIDAR_HEIGHT_RANGE="-2,200".
  • CHANGE_CLASS - specifies that any points that are identified as noise should have their classification changed. This defaults to on, so add CHANGE_CLASS=NO to disable.
  • MARK_WITHHELD - specifies that any points that are identified as noise should be marked as withheld. Use MARK_WITHHELD=YES to enable this behavior. By default this will be the opposite of the CHANGE_CLASS value.
  • DELETE_FEATURES - specifies that any points that are identified as noise should be marked as deleted. This defaults to the same as the MARK_WITHHELD value. Explicitly add DELETE_FEATURES=YES to always mark noise as deleted or DELETE_FEATURES=NO to never mark as deleted.
  • Specify Bounding Box 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 Parameters

    See also 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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