They have a significant effect in terms of describing surface behavior when incorporated in a surface model such as a triangulated irregular network (TIN). Breaklines can describe and enforce a change in the behavior of the surface. Two types of breaklines are included in this layer: hard and soft. Hard breaklines define interruptions in surface smoothness and are typically used to define streams, ridges, shorelines, building footprints, dams, and other locations of abrupt surface change. Soft breaklines are used to ensure that known "Z" (elevation) values along a linear feature (such as a roadway) are maintained in a TIN. Soft breaklines can also be used to ensure that linear features and polygon edges are maintained in the TIN surface model by enforcing the breakline as TIN edges. Soft breaklines, however, do not define interruptions in surface smoothness.
The breaklines in this layer were created using Digital Terrain Model (DTM) data points collected during the production of the 1990's Aerial Images . They were used as input in creating TINs which were the basis for the 3-meter Elevation Contours (1:5,000) datalayer. These breaklines are accurate to National Map Accuracy Standards (+- 1.5 meters).
In ArcSDE the layer name is BREAKLINES_ARC.
The breaklines were produced using the Arc/INFO GENERATE command. The INPUT file was a .GEN file produced with an awk script which contained DTM point coordinates coded either "hard" or "soft". All of these data were extracted from the original DTM files collected on stereo analytic plotters. The Orthophoto Index Grid coverage was used as a CLIP coverage as the DTM points overlap 5-10 percent in both directions.
In the layer's arc attribute table, hard breaklines have an L-ID of 3. The L-ID of each soft breakline is coded 2.
|Date published:||April 1, 2003|
|Last updated:||April 1, 2003|