The main data sources for LAS datasets are lidar data stored in .las or .zlas files, and surface constraints stored in feature classes.
Lidar and point cloud data
General characteristics of point clouds include the following:
- Lidar (light detection and ranging) point clouds stored in .las file format
- Not surface specific
- Sampled to required nominal point spacing, varying from 1 to 15 feet (approximately 0.3 to 5 meters) depending on application
- Every point contains attributes that are stored with the x,y,z data
- Large quantities of point data
- Photogrammetric point cloud data stored in .las files
Surface constraints
Surface constraints are surface features stored in geodatabase feature classes, which are usually derived from a remote sensing technique such as photogrammetry.
Characteristics of photogrammetrically derived breaklines include the following:
- Surface-specific breaks in slope along linear features
- Natural landforms (for example, ridges and valleys)
- Terrain features resulting from earthworks (for example, bulldozed)
- Lake shorelines, creeks, or river shorelines
- Edge of road pavement
- Delineation of void areas (typically obscured by vegetation)
- Minimal attribution
- Typically moderate quantities
Characteristics of GPS points include the following:
- Irregularly spaced
- May or may not represent surface-specific peaks and pits
- Used for control, QA, and benchmarking other data
- Property boundary control points
- Potentially significant attribution per point
- Typically small quantities
The following table describes the types of surface constraints that can be used.
Surface constraint type | Feature class | Z-value source in the feature class | Example data |
---|---|---|---|
Points (x,y,z locations) | Point feature class | Can be either of the following:
|
|
Polygon feature class |
or
| Shoreline delineation | |
Breaklines (hard or soft) | Line feature class |
|
|
Polygon feature class |
| Lake shoreline | |
Clipping polygons (hard or soft) | Polygon feature class |
| Study area boundary |
Erase polygons (hard or soft) | Polygon feature class |
|
|
Replace polygons (hard or soft) | Polygon feature class |
| Water bodies |