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.
County, King, 200307, LiDAR Digital Ground Model Point Density: King County, King County, WA.Online Links:
- None
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.
Planar coordinates are encoded using Row and column
Abscissae (x-coordinates) are specified to the nearest 6
Ordinates (y-coordinates) are specified to the nearest 6
Planar coordinates are specified in Survey feet
The horizontal datum used is North American Datum of 1983, 1991 Adjustment (HPGN).
The ellipsoid used is GRS 80.
The semi-major axis of the ellipsoid used is 20925604.4720406.
The flattening of the ellipsoid used is 1/298.26.
| Value | Definition |
|---|---|
| 1 | 1.Void to Low. Sample points absent to up to 10 pts/100 sq meter density. |
| 2 | 2.Low. Sample point density from 10 to 20 pts/100 sq meters. |
| 3 | 3.Medium. Sample point density from 20 to 40 pts/100 sq meters. |
| 4 | 4.High. Sample point density greater than 40 points/100 sq meters. |
| Value | Definition |
|---|---|
| 1. Void to Low | Polygon has no or very few elevation control points. Even low point areas may have numerous small void areas that are below the resolution of the interpretation. |
| 2. Low | Relative low point density. Low point density areas may contain multiple small void areas below the resolution of the interpretation. |
| 3. Medium | Relative medium density point density. Medium density polygons may include multiple low and possibly void areas below the resolution of the interpretation. |
| 4. High | Relative high point density. High point density polygons may include multiple polygons of lower density, including void areas that are below the resolution of the interpretation. |
| Value | Definition |
|---|---|
| 1. | Up to 10 pts/100 sq. meters |
| 2 | 10 to 20 points/100 sq. meters |
| 3 | 20 to 40 points/100 sq. meters |
| 4 | Greater than 40 points/100 sq meters |
Michael Leathers
King County Geographic Information Center,
GIS Data Coordinator
201 S Jackson St, Suite 706
Seattle, WA 98104
USA
206-263-4867 (voice)
Serves as a guide to the amount of elevation control that was provided by the randomly-spaced elevation sample points. Production elevation models are provided as interpolated lattices based on a standard posting distance. These models do not provide information about the initial data point density used to derive the model. The density data can be use to inform the user as to the amount of LiDAR control in a given area, where data voids occur, and some general information about vegetation canopy density. Detailed investigations regarding LiDAR penetration rates and more accurate point density patterns should be derived from the underlying TINs at a higher point density resolution.
King County ESA/SAO contract wi, Boulder, CO, 2003, King County ESA/SAO Lowland LiDAR Project (Phase I) and King County ESA/SAO Upland LiDAR Project (Phase 2): 3di Technologies, Boulder, CO.
Puget Sound LiDAR Consortium, 2002, Puget Sound LiDAR Consortium LIDAR Elevation Data <http://duff.geology.washington.edu/data/raster/lidar/>: Puget Sound Regional Council, Seattle, WA.
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.
The density quantitative attribute range was calibrated through correlation of grid values generated by the PointDensity function to actual point counts. Final smoothing and dissolve functions to reduce the number of polygons will, in many cases, merge small areas into adjacent polygons. This will have an effect on the absolute accuracy of the density specification relative the polygon it describes. The density attribute also describes an average density for the points in that polygon. Actual point density and distribution often varies considerably at the sub-polygon level.
The bounds of the density polygons is the result of some generalization, smoothing and aggregation of subpolygon density information. The posting resolution of the underlying grid from which the polygons were derived also affects the postional accuracy of the data. Horizontal accuracy of the density polygon bounds is approximately 6 - 12 feet.
Not applicable
Density interpretations will eventually cover all portions of the combined King County ESA/SAO and PSLC project areas.
All polygons are attributed with a density attribute. There are no 'islands'.
Are there legal restrictions on access or use of the data?
- Access_Constraints:
- A cooperative data sharing arrangement between the Puget Sound LiDAR Consortium and King County is allowing certain formats of the LiDAR data to be distributed with out license or restriction. Certain processing and data handling charges for necessary cost recovery may apply. Access to raw mass point files is by special request and request evaluation only.
- Use_Constraints:
- This data is provided for use as a general guide to the amount of surface elevation control (sample spacing) used in creation of the bare-earth digital surface model. Even though the interpretation has been generalized, it is a important supplement for users in evaluating relative accuracies and control spacing where penetration to 'true ground' may vary considerably.
Dennis Higgins
King County GIS Center, Client Services
Manager, Client Services Division
201 S Jackson St, Suite 706
Seattle, WA 98104
USA
206-263-4523 (voice)
LiDAR Digital Ground Model point density, txxrxx_den.shp
King County disclaims any warranty of use of any digital product or data beyond that for which it was designed.
| Data format: | ArcInfo Shapefile |
|---|---|
| Network links: |
\\gisdw\kclib\plibrary3\idxptrmbr\dgm_density |
| Media you can order: |
CD-R, DVD+R
(format CD: Read-only, DVD: DVD+R read-only)
|
Contact KCGIS Client Services <http://www.metrokc.gov/gis/services/> for cost of reproduction and delivery
Michael Leathers
King County GIS Center,
GIS Data Coordinator
201 S Jackson St, Suite 706
Seattle, WA 98104
USA
206-263-4863 (voice)
mike.leathers@metrokc.gov