A LAS dataset stores references to one or more .las files on disk, as well as to additional surface features. A .las file is an industry-standard binary format for storing airborne lidar data. Optimized .las files (.zlas) are also supported with the LAS dataset. The LAS dataset allows you to examine .las files in their native format quickly and easily, providing detailed statistics and area coverage of the lidar data contained in the .las files.
A LAS dataset can also store references to feature classes containing surface constraints. Surface constraints are breaklines, water polygons, area boundaries, or any other type of surface feature enforced in the LAS dataset. Surface constraints are stored in geodatabase feature classes or shapefiles, which are usually derived from some sort of remote sensing technique such as photogrammetry. Surface constraints are enforced when the LAS dataset is drawn as a TIN surface model.
The LAS dataset does not import point data contained in the .las files. It stores a reference to those .las files and surface constraints.
The list below includes common examples of how to benefit from using LAS datasets to incorporate lidar data in ArcGIS Drone2Map. With LAS datasets, you can do the following:
- Store references to many .las files and surface data at once for a specific project.
- Quickly display lidar data as point clouds or a triangulated surface in 2D or 3D.
- Visually compare the lidar points to existing GIS data for data validation, such as building data.
- Quickly conduct a statistical analysis on .las files and lidar points.
- Conduct initial quality assurance and quality control, such as assessing data coverage and point sample density, for newly acquired lidar data.
- Incorporate additional breaklines or surface features with lidar.
- Update with newly acquired LAS or surface data.
- Share LAS dataset data using the mosaic dataset.
You can quickly change the view of the LAS dataset into a TIN-based surface, similar to the TIN or terrain dataset display. The LAS dataset allows you to work with points classified into different feature types. There are several point and surface symbology renderers available for LAS datasets. The most common symbology for LAS datasets can be accessed quickly from the Symbology pane. Surface constraints are enforced when the LAS dataset is drawn as a TIN.
The LAS dataset default display in ArcGIS Drone2Map is as a point cloud with no filter applied. That means that all the lidar points display initially if zoomed to an extent, where thinned points display. Also, ArcGIS Drone2Map allows single .las and .zlas files to be displayed and used with all the same functionality as a LAS dataset.
A LAS dataset pyramid structure is used to improve 3D display performance for a LAS dataset in ArcGIS Drone2Map. It does this by organizing and indexing the points in a way that optimizes 3D display queries. A prompt will appear when a LAS dataset is added to a map or a scene that does not have a pyramid built; this prompt will request that you build a LAS dataset pyramid.
When a LAS dataset, or .las or .zlas file, is added to a 3D map in ArcGIS Drone2Map, the points are symbolized with an elevation renderer, and eye-dome lighting is applied by default. Eye-dome lighting is a shading technique that improves the perception of depth and contour when viewing LAS datasets. When a LAS dataset, or .las or .zlas file, is added to a 2D map in ArcGIS Drone2Map, the points are drawn with an elevation renderer only.
The LAS dataset is a complement to terrain dataset- and mosaic dataset-based workflows. For example, it is common to add newly acquired lidar data to a terrain dataset in ArcGIS Pro. The LAS dataset can be quickly generated first in ArcGIS Drone2Map to conduct an initial quality assurance and quality control check on the lidar data. This LAS dataset provides all of the necessary information to know that the lidar data meets the necessary quality standards before importing into the terrain dataset.
Dimensions and size of .las files
For best performance, consider the following recommendations for dimension and size for .las files:
- The client machine should have direct access to data on a local internal drive, not across network or slower external drives.
- Use .zlas files when using lidar over a network.
- Build a LAS dataset using .las files from the same project (that is, specifications and study area). LAS datasets are not meant to compile data from disparate sources and study areas. For that purpose, use a mosaic dataset.
- Generally, it is beneficial for a LAS dataset to be constructed with tiled .las files. The .las files should not contain lidar data in large strips or flight lines unless the .las files have been indexed and contain a .lasx file for each .las file.
- Calculate statistics to provide the LAS dataset .lasx files. These auxiliary files contain a statistical analysis and spatial index calculated for each .las file. The spatial index improves the overall performance of a LAS dataset.
- Generally, it is a good practice to keep .las file sizes to approximately 500 MB when .lasx files are created. However, there are many situations in which .las files are much larger, and the spatial index in the .lasx files allows ArcGIS Drone2Map to better handle these very large files. A size limit becomes less significant in ArcGIS Drone2Map if there is a spatial index present. The size recommendations are for practical data management issues of larger file sizes, for example, file or disk fragmentation.
- When statistics are not calculated, the LAS tiles should be contiguous, not overlapping, and approximately 500 MB or less in size.