Processing of a LiDAR-derived surface (DEM or TIN) so that standing water bodies are flat and flowing water bodies are level from bank-to-bank. Additionally, surfaces of streams, rivers, and long reservoirs demonstrate a gradient change in elevation along their length. In traditional maps that are compiled photogrammetrically, this process is accomplished automatically through the inclusion of measured breaklines in the DTM. However, because LiDAR does not inherently include breaklines, a DEM or TIN derived solely from LiDAR points will depict water surfaces with unsightly and unnatural artifacts of triangulation.

Hydro-flattening typically involves the addition of corrected breaklines along the banks of the specified water bodies. These breaklines establish elevations for the water surfaces that are consistent with the surrounding topography and produce aesthetically acceptable water surfaces in the final DEM or TIN.

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