Metadata

Lidar projects should include project-level metadata as well as file-specific metadata. In addition, your data management requirements will likely add metadata specific to your organization. In most applications, it is recommended to store the complete (verbose) metadata with the source data, and then copy key metadata (and add processing notes) into the mosaic dataset attribute table used to manage any derived data.

Since the DTM and DSM rasters are to be managed the same as other elevation datasets, these best practices focus on preparing data and metadata for that later step.

All commonly used metadata should be populated into the attribute tables of the source mosaic datasets (to be created from the DTM and DSM rasters in Creating mosaic datasets and serving the raster data) for easy access for queries and sorting. The list of the recommended field names and data types for commonly used metadata can be found in the Elevation best practices.

If users require access to more extensive metadata, it is best to store the metadata as digital files in a network-accessible location with appropriate access permissions. Detailed metadata can then be exposed to users via a field in the attribute table populated with the path and file name to allow download. This will enable users to locate the detailed metadata for any record in the system.

Specific metadata should be noted for later steps in this workflow, as follows:

• Ensure that the DSM and DTM rasters created from lidar include metadata to refer back to the original source data and the settings used to create the rasters.
  • The geoprocessing tools LAS Dataset To Tiled Rasters and Terrain To Tiled Rasters will write metadata regarding the source datasets into the .xml files created for each output raster.
• Make note of the coordinate system and units for the lidar data, keeping in mind that the vertical units may be different from the horizontal.
• Verify whether the vertical units represent orthometric or ellipsoidal height.
  • Most organizations manage data in orthometric height and then, if ellipsoidal height is required, use a function to convert on the fly. Refer to Elevation best practices.
• Determine whether existing feature classes are available to define the extents of each LAS file, and also for the complete lidar project boundary.
• Identify the original lidar project requirements with regard to the following:
  • Pulse density (per square area) or pulse spacing (feet or meters between points)
  • Point density or point spacing
  • Classification requirements (list of classes to be identified by the data provider)

This completes the preparation process, and you can now begin the multistage workflow. The first stage of the workflow uses a LAS dataset to perform quality control and possible editing of the lidar data in a single project, and to determine the appropriate parameters to create the DSM and DTM rasters in a later stage. Note that if you have multiple lidar projects to manage, the first three stages will be repeated for each project, and then multiple projects will be combined into a scalable system in Create mosaic datasets and serve the raster data.