Every lidar point can have a classification code assigned to it that defines the type of object that has reflected the laser pulse. Lidar points can be classified into a number of categories, including bare earth or ground, top of canopy, and water. The classes are defined using numeric integer codes in the LAS files.
Lidar points stored in LAS files are typically classified into categories using specialized classification tools outside of ArcGIS Pro. This classification is usually completed by setting parameters based on the terrain and then running algorithms on the point cloud to determine the feature type associated with each point. The classification code assigned to each point is written to the LAS file and, in most cases, adheres to the American Society for Photogrammetry and Remote Sensing (ASPRS) standard.
When a classification is carried out on lidar data, points may fall into more than one category of the classification. Classification flags are used to provide a secondary description or classification for lidar points. In later versions (LAS 1.1 and later), class flags were used to solve this problem. Classification flags were added to the LAS standard to mark points with information that supplements the traditional classification. Synthetic, key-point, withheld, and overlap flags can be set for each lidar point. These flags can be set along with the classification codes. For example, a water record can be given a classification code for water (9) as well as a withheld flag. The point will remain in the dataset but will be withheld from any additional analysis on the LAS files.
In many cases, LAS files may not be fully or correctly classified when used as input for the GIS tools in ArcGIS Pro. ArcGIS Pro provides the LAS dataset and associated tools to enable classification or data cleanup of classification codes and classification flags residing in the LAS files.
The list below includes common examples of how you can benefit from editing LAS datasets:
- Manually fix errors in class codes.
- Visually compare the lidar points against existing GIS data for data validation, such as building data.
- Classify lidar points using GIS features.
- Reclassify lidar points by manually selecting one or many lidar points.
- Change all classification codes currently in the LAS dataset.
- Add or remove LAS files from a LAS dataset to increase or decrease the data area extent.
- Interactively measure 3D distances between visible features, such as power lines and trees.
- Use the lidar points as backdrop data to digitize new GIS features, such as street furniture.
- Measure height offsets and distances between points or overlapping datasets or flight lines.
- View high-accuracy control points alongside the LAS points and compare height differentials.
- View and compare two LAS datasets collected at different times for the same area of interest.
The interactive and geoprocessing tools in ArcGIS Pro provide the ability to edit classification codes present in LAS files.
Geoprocessing tools for classification editing
Geoprocessing tools allow you to automate editing of classification codes.
| Geoprocessing tool | Description |
|---|---|
| Classify LAS Ground | Classifies unclassified LAS points into ground points. |
| Classify LAS Building | Classifies building rooftop points in aerial lidar data. |
| Classify LAS By Height | Reclassifies lidar points based on their height from the ground surface. |
| Set LAS Class Codes Using Features | Changes lidar classification codes assigned to lidar points based on their proximity to feature data. For example, breaklines representing water boundaries can be used to classify all points within the water boundaries as class code 9 to represent water. |
| Set LAS Class Codes Using Raster | Classifies LAS points using cell values from a raster dataset. |
| Locate LAS Points By Proximity |
Identifies lidar points within the three-dimensional proximity of z-enabled features while also providing the option to reclassify the points and export them to an output feature class. |
| Change LAS Class Codes |
Modifies the classification codes for LAS files referenced by a LAS dataset. This tool reclassifies one set of classification codes into another, which is particularly useful for updating the classification of LAS files generated before the introduction of classification standards in the LAS 1.1 specification. The tool can be used to ensure that such data conforms to the current standards. |
Classifies LAS points from overlapping scans of aerial lidar surveys. | |
| Classifies LAS points with anomalous spatial characteristics as noise. |