Types of source data supported in terrain datasets
Release 9.3 Last modified April 28, 2009	Print all topics in : "Understanding terrain datasets"

Common types of data used to build terrains

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 (e.g., ridges and valleys)
  
• Terrain features resulting from earthworks (e.g., 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 is 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	Shape geometry; x,y,z per point Attribute column holding a z-value for each point	Spot heights Survey points GPS points
	Multipoint feature class	Shape geometry; x,y,z per point Attribute column holding one z-value per shape	Lidar points Sonar points
	Line feature class	Shape geometry; x,y,z per vertex Attribute column holding one z-value per shape	Contours
	Polygon feature class	Shape geometry; x,y,z per vertex Attribute column holding one z-value per shape	Shoreline delineation
Breaklines (hard or soft)	Line feature class	Shape geometry; x,y,z per vertex Attribute column holding one z-value per shape No height source; z-values interpolated for each feature from the surface before being added	Contours Edge of pavement Roads Waterlines (streams, rivers, canals, shorelines)
	Polygon feature class	Shape geometry; x,y,z per vertex Attribute column holding 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 holding 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 boundry
Erase polygons (hard or soft)	Polygon feature class	Shape geometry; x,y,z per vertex Attribute column holding one z-value per shape No height source; z-values interpolated for each feature from the surface before being added	Lake shorelines Obscured areas (dense forest canopy)
Replace polygons (hard or soft)	Polygon feature class	Shape geometry; x,y,z per vertex Attribute column holding one z-value for all vertices in each shape	Water bodies
Value Fill (hard or soft)	Polygon feature class	Shape geometry; x,y,z per vertex No height source; z-values interpolated for each feature from the surface before being added	Land-use codes

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