| 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 2017-11-01 during low tide surveys on 22 and 23 July 2021. The point clouds from each survey are tiled into 500 by 500 meter tiles to reduce individual file sizes. The Fort Stevens point clouds have a total of approximately 496 million points, with an average point density of 386 points per-square meter and an average point spacing of 5 centimeters. The Benson Beach point clouds have a total of approximately 476 million points, with an average point density of 363 points per-square meter and an average point spacing of 5 centimeters. Each point in the point clouds contains explicit horizontal and vertical coordinates, color, and point class (either 0 [unclassified] or 7 [noise]). In addition, each point has a confidence value (calculated by Agisoft Metashape during point cloud creation) stored as an extra byte. The point confidence value was used to identify and classify erroneous points likely resulting from poor surface reconstruction due to water, vegetation, or areas of uniform surface texture (such as sand of uniform color). All points with confidence less than 4 have been classified as class 7 (noise). All other points have been left unclassified (class 0). Some areas of noise resulting from poor terrain reconstruction may remain unclassified in 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 approximately 70 percent overlap between images from adjacent lines. The camera was triggered at 1 Hz using a built-in intervalometer. The UAS was flown at an approximate altitude of 120 meters above ground level (AGL), resulting in a nominal ground-sample-distance (GSD) of 3.2 centimeters per pixel. 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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