The data were not stored as production version elevation models at the King County township-range (idxptrmbr) tile index level. They are stored only at the idxp7500 tile index level. This index is a State Plane orthogonal fishnet grid over the extent of the ESA/SAO project area and environs. Access to the metadata and tile index spatial file will likely be necessary for proper identification of tiles of interest.
The Puget Sound LiDAR Consortium (PSLC) data which is being processed coincidently with the King County data to the same tiling scheme has last-returns embedded as part of their all-return file. Only the first returns were processed from this record. Therefore last return randomly-spaced ASCII elevation data files are not available from King County at this time for the PSLC project area.
LiDAR data processing was used to produce the x,y,z elevation points using vendor proprietary lidar data processing software. Within this integrated process an atmospheric correction was made, which is especially important in regions of relatively low elevation.
Data by flight line was combined in a merge process that eliminates redundant points. Data was also clipped into more manageable one km x one km bounds. Noise or anomalous returns were filtered from all data during this processing step. The data was quality checked using commercial software, Spectra Precision TerraModel and TerraVista.
All elevation data was processed on a point by point basis for ellipsoid to orthometric height conversion using the National Geodetic Survey (NGS) Geoid Model, GEOID99. Datum and coordinate system conversion from WGS84 to the Washington State Plane coordinate system was performed using U.S. Army Corps of Engineers CorpsCon software algorithms.
After receipt from 3di Technologies, the data media was cataloged, and the media contents were logged. The ASCII files were retiled into the King County idxp7500 tiling scheme. This resulted in creation of larger files where several 1 x 1 km 3di tiles were appended and clipped to form one 7500 ft x 7500 King County tile. The ASCII records were also appended with a integer identifier resulting in a final record format of identifier, easting, northing, and elevation value.
Some of the initial deliveries from the Vendor were not processed to the correct horizontal datum. Reprojection of those tiles was performed using ArcInfo Project command. Results of the reprojection algorithm were confirmed by a sample set also projected using U.S. Army Corps of Engineers CorpsCon algorithm. The resulting output files carry more significant figures to the right of the decimal than the input files. These were not truncated nor rounded to the original 2 decimal precision. Not all files required reprojection so some files will have 2 decimal precision and others will have more digits to the right of the decimal point even though the data is only 2 decimal precision.