Breaklines

Breaklines assist in the development of hydro-flattened DEMs, if they are required for a project. LiDAR intensity images in combination with the elevation data can be used to create a pseudo stereo pair which then allows a photogrammetric system operator to “see” in 3D and use this technique to better determine the location of ground features. This technique is often defined as lidargrammetry, and is used extensively in the creation of breaklines. The first step is to create synthetic LiDAR stereo-pairs using a software such as the GeoCue LiDAR Pak software. These synthetic LiDAR stereo pairs can then be stereoscopically compiled to create breakline features. SOCET for ArcGIS is often used for this compilation. SOCET for ArcGIS embeds the photogrammetrically-compiled features into an ESRI 10.x geodatabase. This ultimately means there is no CAD to GIS file translation required and that the resultant photo interpreted data is topologically correct and GIS ready upon completion. Although this requirement is project specific, breaklines are commonly collected for the following features.

(1) Streams and Rivers. The banks or land/water interface shall be depicted for all linear hydrographic features of a certain width and length (e.g. at least 50 feet in width and ½ mile in length). Islands greater than a certain size (e.g. ½ acre) will be excluded as “holes” in the Streams and Rivers features. Each vertex placed needs to maintain vertical integrity, including monotonicity and connectivity. Exemptions to monotonicity may occur due to complex branch networks. All elevations are at or slightly below the surrounding terrain.

(2) Ponds and Lakes. The land/water interface is depicted for all water bodies, such as lakes, ponds, and reservoirs, at a constant elevation that are usually 1 acre in size or greater. Every vertex on each feature must be placed at the same elevation and all elevation is set at or slightly below the surrounding terrain. Islands greater than ½ acre in size are usually excluded as “holes” in the Ponds and Lakes features.