Types of source data supported in terrain datasets
Photogrammetrically derived mass points
- Irregularly spaced
- Surface-specific peaks and pits
- Pseudo regularly spaced points gathered to achieve a specified minimum sample density/nominal point spacing
- Minimal attribution
- Typically moderate quantities
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
Lidar points
- Irregularly spaced
- 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 only
- Limited attribution (what's available typically not very useful to end users)
- Typically in large quantities
Sonar
- Similar to lidar in terms of use in defining a surface
- Dense, non-surface-specific, irregularly spaced points
Contour lines
- Minimal attribution
- Often vectorized from scanned maps in large quantities or generated in CAD applications in smaller quantities for large-scale engineering projects
Points, lines, polygons (mass, break, clip, erase, replace)
The thematic data types used to derive a surface are stored in the geodatabase as features with different geometry types. These types are points, multipoints, polylines, and polygons. These geometry types can be incorporated into the terrain surface in different ways. You control how a feature is used by setting its surface feature type (SFType). The following table shows the relationship of different SFTypes, types of feature classes that can be used for each SFType, height source options, and thematic data examples.
Surface feature types in terrain datasets
Surface feature type |
Feature class |
Z-value source in the feature class |
Thematic data type examples |
---|---|---|---|
Mass points (x,y,z locations) |
Point feature class |
or
|
|
Multipoint feature class |
or
|
|
|
Line feature class |
or
|
|
|
Polygon feature class |
or
|
|
|
Breaklines (hard or soft) |
Line feature class |
|
|
Polygon feature class |
|
|
|
Clipping polygons (hard or soft) |
Polygon feature class |
|
|
Erase polygons (hard or soft) |
Polygon feature class |
|
|
Replace polygons (hard or soft) |
Polygon feature class |
|
|