| Description |
This portion of the data release presents topographic point clouds of the ocean beach at Fort Stevens State Park, OR, and Benson Beach at Cape Disappointment State Park, WA. The point clouds were derived from structure-from-motion (SfM) processing of aerial imagery collected with unoccupied aerial systems (UAS) on during low tide surveys on 7 and 8 August 2017. The point clouds from each survey are tiled into 1000 by 1000 meter tiles to reduce individual file sizes. The Fort Stevens point clouds have a total of 271,915,544 points, with an average point density of 407 points per-square meter and an average point spacing of 5 centimeters. The Benson Beach point clouds have a total of 301,569,130 points, with an average point density of 558 points per-square meter and an average point spacing of 4 centimeters. The point clouds have not undergone any point classification (all points are classified as 0), but contain explicit horizontal and vertical coordinates, and color. Noise resulting from water and waves in the surf zone, and other areas of poor terrain reconstruction have not been removed from the point clouds. The raw imagery used to create the point clouds was acquired with a UAS fitted with a Ricoh GR II digital camera featuring a global shutter. The UAS was flown on pre-programmed autonomous flight lines spaced to provide at least 66 percent overlap between images from adjacent lines. The UAS was flown at an approximate altitude of 120 meters or less above ground level (AGL). The raw imagery was geotagged using positions from the UAS onboard single-frequency autonomous GPS. Survey control was established using temporary ground control points (GCPs) consisting of a combination of small square tarps with black-and-white cross patterns and temporary chalk marks placed on the ground. The GCP positions were measured using dual-frequency post-processed kinematic (PPK) GPS with corrections referenced to a static base station operating nearby. The images and GCP positions were used for structure-from-motion (SfM) processing to create topographic point clouds, high-resolution orthomosaic images, and DSMs. The point clouds are formatted in LAZ format (LAS 1.2 specification). [More]
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