Every lidar point can have a classification 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 different classes are defined using numeric integer codes in the LAS files. Classification codes were defined by the American Society for Photogrammetry and Remote Sensing (ASPRS) for LAS formats 1.1, 1.2, 1.3, and 1.4. ArcGIS supports all versions of LAS. LAS version 1.4 is the latest LAS version and adds additional point classification and information. For additional information on classification codes and flags, see Storing lidar data. The Classification Codes, Return Values, and Classification Flags can be used to filter the points for display.
The Layer Properties of a point cloud scene layer allows you to select which points are drawn and change the display of the data contributing to the point cloud in ArcGIS AllSource. A point cloud scene layer can reference many LAS files derived from lidar, and the point classification codes and flags that have been assigned within the files will be listed on the Point Cloud Layer Filter tab on the Layer Properties dialog.
Once the filter options have been chosen, any further symbology changes will honor the selected filters. Follow these steps to access the Point Cloud Layer Filter tab.
- Select a point cloud scene layer in the Contents pane.
- Right-click on the point cloud scene layer and select Properties.
- From the Layer Properties dialog box, click the Point Cloud Layer Filter tab.
- From the Point Cloud Layer Filter tab, click the desired point cloud scene layer filter.
Point Cloud Layer Filter options
The Classification Codes or Return Values will be displayed when a check mark is displayed next to the desired filter. Classification Flags are slightly different.
- Checked: All points with this flag will be displayed and points that do not have this flag will not be displayed. The check makes it an absolute requirement to have this flag in order to be displayed.
- Unchecked: Points with this flag will never be displayed.
- Filled check: This flag does not contribute to point filtering. Points with this flag will be displayed, but if a point that does not have this flag is represented by another flag that is set to be displayed, then points that do not have this flag can also be displayed. This is the default.
| Point filters | Description |
|---|---|
| Classification Codes | Every lidar point that is postprocessed can have a classification 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 different classes are defined using numeric integer codes in the LAS files. |
| Return Values | An emitted laser pulse can have up to five returns depending on the features it is reflected from and the capabilities of the laser scanner used to collect the data. The first return will be flagged as return number one, the second as return number two, and so on. |
| Classification Flags | 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. For example, a lidar return from water may need to be removed from the final output dataset, but it still should remain and be managed in the LAS file as a collected lidar point. With LAS version 1.0, a lidar point could not simultaneously maintain two assigned classification attributes. In later versions (LAS 1.1, 1.2, 1.3, and 1.4), classification flags could be used to solve this problem. Synthetic, Overlap, Key Point, and Withheld flags can be set for each lidar point. These flags can be set along with the classification codes. |