Most of these data were acquired for the Puget Sound Lidar Consortium by TerraPoint,LLC, in early 2000 and early 2001. TerraPoint flew a multiple-return scanning laser altimeter in a small fixed-wing aircraft with a circa 0.9 meter on-the-ground laser spot, nominal across- and along-track pulse spacing of 1.5 meters, and 50% overlap of adjacent flight lines, providing an average of circa 1 pulse/square meter. Some of these data (Bainbridge Island) were acquired for Kitsap PUD in 1996-1997. Average pulse spacing of the Bainbridge data was similar. The data are in Stateplane projection, Washington North zone (ARC zone 5601, FIPS zone 4601). The vertical datum is NAVD88, horizontal datum is NAD83, 1991 adjustment. Horizontal units are US Survey Feet. Raster cells (grid cells, image pixels) are 6 ft square. Elevations are recorded in floating-point feet. The ARC-INFO projection information for these data is Projection STATEPLANE Zone 5601 Datum HPGN Zunits FEET Units FEET Spheroid GRS1980 Xshift 0.0000000000 Yshift 0.0000000000 Parameters Gridded elevation data (DEMs), shaded-relief images, and geo-registered shaded relief images are available online at http://pugetsoundlidar.org. ------------------------------------ The contractor delivered all-return points, a first-return surface, bare-earth points, and a gridded bare-earth DEM. Bare-earth points were separated from points in the canopy and on structures by automatic geometric filtering (virtual deforestation, or 'VDF'). The bare-earth DEM was produced by sampling a TIN (Triangulated Irregular Network) constructed from these points, with few--if any--modifications. The bare-earth DEM should be considered preliminary. (1) Elevations within open-water areas are suspect, largely reflecting interpolation to the nearest shoreline points. (2) Some elliptical areas have unusually noisy elevation data on one flightline, resulting in no ground points surviving initial VDF. There are bad elevation values at the boundaries of some of the tiles within which data were post-processed. There is one bad flightline on the Kitsap Peninsula. These areas are identified in bad.e00, an ARC-INFO export file of a polygon coverage, which is included with these data. (3) In some timbered areas, initial VDF has identified a very large fraction of returns as from canopy and has not removed some points that are probably in the canopy. At some point the in the not-too-distant future we hope to reprocess the all-return data to fix problems (1) and (2). Problem (3) cannot be entirely rectified, but it may be possible to slightly improve the bare-earth ground model in these areas. ------------------------------------ Version 0.3 note: Contractor has not been snapping grids to defined coordinates. When such grids are merged, there can be shifts of up to 1/2 pixel at each merge operation. Bare-earth grids have now been snapped, with shifts of up to 1/2 pixel, and they will not shift with further MERGEs. ------------------------------------ Disclaimer ---------- Considerable care has been taken to see that these data and derived images are as accurate as possible. We believe most of these data are adequate for determination of flood hazards, for geologic mapping, for hydrologic modelling, for determination of slope angles, for modelling of radio-wave transmission, and similar uses with a level of detail appropriate to a horizontal scale of 1:12,000 (1 inch = 1,000 feet) or smaller and vertical accuracy on the order of a foot. Locally, the data are of considerably poorer quality. You should carefully determine the place-to-place accuracy and fitness of these data for your particular purposes. For many purposes a site- and use-specific field survey will be necessary. Enjoy! The Puget Sound Lidar Consortium March 2002