There are two major data sources to LAS datasets: lidar data stored in LAS files and surface constraints stored in shapefiles or feature classes.
Lidar
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:
- 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
- Often, but not always, filtered to bare earth points
- Every point contains attributes that are stored with the x,y,z data
- Large quantities of point data
A LAS dataset is designed and optimized to support LAS files from an airborne lidar collection. The LAS dataset can support lidar data in LAS format from a terrestrial collection, however, they should only be displayed as points. With an airborne collection you can visualize the LAS dataset in ArcMap, ArcScene, and ArcCatalog as points or as a triangulated surface.
Surface constraints
Surface constraints are surface features stored in either geodatabase feature classes or shapefiles, which are usually derived from some sort of remote sensing technique like photogrammetry.
Photogrammetrically derived breaklines:
- 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, river shorelines
- Edge of road pavement
- Delineation of void areas (usually obscured by vegetation)
- Minimal attribution
- Typically moderate quantities
GPS Points:
- 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
Surface constraint type | Feature class | Z-value source in the feature class | Thematic data type examples |
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Points (x,y,z locations) | Point feature class |
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Polygon feature class |
or
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Breaklines (hard or soft) | Line feature class |
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Polygon feature class |
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Clipping polygons (hard or soft) | Polygon feature class |
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Erase polygons (hard or soft) | Polygon feature class |
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Replace polygons (hard or soft) | Polygon feature class |
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