The density data is available in the same tiling scheme as the the primary bare-earth digital ground elevation data (dgm). The King County tile scheme is based on the underying PLSS as described by the idxptrmbr tile index. Individual tiles are identified as TxxRxx_den.
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.
The retiled ASCII point files were AWKed to output .gen files of the format: 1, easting, northing, elevation. The constant value of 1 was used to indicate that all points should be treated as mass points.
Digital Ground Model (bare-earth) .gen files were built for input to the TIN creation function. The .gen files included all points of the subject tile plus a 100-foot buffer of all adjacent tiles. The composite ASCII .gen file was AWKed to create an output file of form: 1,easting, northing, elevation. The constant value of 1 is used to indicate that all points should be treated as Masspoints during the tinning process.
The retiled ASCII point files were built into TINs using ArcInfo CREATETIN command with no (0.0) proximity tolerance.
ArcInfo TINARC-point all idxp7500 TINs that comprise a township-range tile
ArcInfo GRID POINTDENSITY tin # # SIMPLE,3.208,circle,17.7 to generate a grid interpretation of the point density
Tins, and thus pointdensity grids, extend 100 ft beyond input idxp7500 tiles. ArcInfo GRID GRIDCLIP used to clip back only 25 overlap with adjacent tiles to remove lower density areas due to edge effect
Resulting idxp7500 grids are GRID MERGED to form composite grid of density values.
Merged grid GRID RECLASSED using pre-defined remap table to reduce continuous range of data values to discrete 4 classes.
GRID BOUNDARYCLEAN function with ASCEND, TWOWAY arguments used to aggregrate and regroup pixel clusters into a reduced number of zones.
For composite grids that have NODATA areas, a NULL mask applied.
Final grids created by clipping merged grids to exact idxptrmbr tile bound.
GRIDPOLY used to convert grid to polygon
Attributes added to PAT and populated
PROJECTDEFINE used to define projection header
Coverage exported as shapefile.
This MBR is defined by right angle corners and four orthogonal bounds that are adjusted to the nearest 100 foot State Plane Zone 5061, HPGN position. This results in a series of overlapping tiles that fully encompass all sections within that township. The tiling scheme is defined by the spatial index called idxptrmbr (index polygons for township- range, minimum bounding rectangle). Tiles have only been created for those townships where sufficient LiDAR data was available for contouring.