Every lidar point can have a classification code assigned to it that defines the type of object that has reflected the laser pulse. You can classify lidar points 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.
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. You can set synthetic, key-point, withheld, and overlap flags for each lidar point. You can set these flags along with the classification codes. For example, you can give a water record 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 tools to enable classification or data cleanup of classification codes and classification flags residing in a LAS dataset, or individual .las or .zlas files.
The interactive selection tools in ArcGIS Pro allow you to edit classification codes manually. You can use these selection tools to select and classify points directly in a 3D scene or, optionally, shift your scene into a side-on viewpoint using profile viewing.
The list below includes common examples of how you can benefit from editing LAS 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.
- 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.