Manage lidar collections with LAS datasets

Create a LAS dataset and perform quality control

Following the preparation described above, the first stage begins with the creation of a LAS dataset (LASD) to reference all LAS or zLAS files in the project. Refer to the ArcGIS help for details on Creating a LAS dataset.

• Be sure to define the proper coordinate system in the properties of the LAS dataset.
• Add the LAS or zLAS files to the LAS dataset, and calculate full statistics on all files.
• Review statistical data within the LAS dataset for quality control (QC) purposes:
  • Ensure the point classifications meet the project requirements.
  • Verify zMin and zMax values (excluding points classified as noise) are reasonable (for example, no below-ground points or high points are included).
• Perform a visual review of the data to ensure noise has been properly classified, or use the editing tools to reclassify erroneous points.
• Create a raster representation of the outgoing pulse density using the LAS Point Statistics as Raster tool (set Method to PULSE_COUNT) to ensure the data meets project specifications in all important areas. This raster can be summarized at relatively low resolution (for example, 5 to 20 times your desired DTM resolution), but note that you will need to normalize the values according to cell size. For instance, if you summarize pulse density at 20-meter resolution, divide all values by 20², equaling 400, so the raster values represent pulses per square meter.
• A similar raster representation of the density of ground points is also recommended, to be used to determine the appropriate resolution for the DTM. This can be created as follows:
  • Load a LAS dataset covering your full project into ArcGIS Desktop, and filter for ground points only.
  • Open the LAS Point Statistics as Raster tool, load the LAS dataset from the table of contents into the tool (to ensure the filter for ground points only is honored) and set Method to POINT_COUNT.
  • Create this raster at the same spatial resolution as the outgoing pulse density raster, and as above, normalize so each cell represents point density per square meter.
• Add any additional requirements from your organization to complete the QC process on the lidar data before proceeding.

Determine project extents

It is recommended to add a polygon to the LAS dataset that outlines the usable extent of the lidar data (the Soft Clip option on the Surface Constraints tab of the LAS Dataset Properties dialog box). This polygon will prevent problems with attempts to interpolate and fill voids around the project boundary. Note that the usable extent of the lidar data is distinguished from all data to emphasize that lidar points at the extreme edges of the dataset should generally not be used.

• In most cases, your lidar data was acquired based on a desired project area, so a polygon defining the desired project extent will likely exist.
• If a project extent polygon does not already exist, you can create one using different methods:
  • Manually create a polygon to approximate the project extents.
  • Synthesize a data boundary as described in Data area delineation from lidar points in the ArcGIS help.

• Note that a complicated polygon can diminish performance. You should use a generalized polygon (with minimal number of vertices) that is conservatively inside the extreme edges of the lidar points.

Overlay your project polygon with the pulse density raster to ensure that the project coverage is complete, or identify any areas that may have been omitted.