Data supported by a LAS dataset

The two main data sources for LAS datasets are lidar data stored in .las files and surface constraints stored in feature classes.

Lidar data

Lidar (light detection and ranging) is an optical remote sensing technique that uses laser light to densely sample the surface of the earth, producing highly accurate x,y,z measurements.

General characteristics of lidar include the following:

• Lidar point clouds stored in LAS 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.

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: Shape geometry; x,y,z per vertex Attribute column containing one z-value per shape	Spot heights Survey points GPS points
	Polygon feature class	Shape geometry; x,y,z per vertex or Attribute column containing one z-value per shape	Shoreline delineation
Breaklines (hard or soft)	Line feature class	Shape geometry; x,y,z per vertex Attribute column containing one z-value per shape No height source; z-values interpolated for each feature from the surface before being added	Contours Edge of pavement Water lines (streams, rivers, canals, and shorelines)
	Polygon feature class	Shape geometry; x,y,z per vertex Attribute column containing one z-value per shape (such as a shoreline) No height source; z-values interpolated for each feature from the surface before being added	Lake shoreline
Clipping polygons (hard or soft)	Polygon feature class	Shape geometry; x,y,z per vertex Attribute column containing one z-value per shape (such as a shoreline) No height source; z-values interpolated for each feature from the surface before being added	Study area boundary
Erase polygons (hard or soft)	Polygon feature class	Shape geometry; x,y,z per vertex Attribute column containing one z-value per shape No height source; z-values interpolated for each feature from the surface before being added	Lake shoreline Obscured areas (dense forest canopy)
Replace polygons (hard or soft)	Polygon feature class	Shape geometry; x,y,z per vertex Attribute column containing one z-value for all vertices in each shape	Water bodies