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.
County, King, 200307, LiDAR Last Return ASCII Elevation Data: King County, King County, WA.Online Links:
- None
Planar coordinates are encoded using Row and column
Abscissae (x-coordinates) are specified to the nearest .01
Ordinates (y-coordinates) are specified to the nearest .01
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.
Michael Leathers
King County Geographic Information Center,
GIS Data Coordinator
201 S Jackson St, Suite 706
Seattle, WA 98104
USA
206-263-4867 (voice)
The last return elevation data is a superset of the bare-earth digital ground model. The data is provided for uses where determination of the relationship between the bare-earth model and the last LiDAR return is necessary. The data may also locally serve to help identify sub-canopy vegetative cover status.
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.
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.
There are no attributes as the data is provided in comma delimited, ASCII files with no header. The order of the values in the file is unique record identifier, easting, northing and elevation value.
Horizontal accuracy specification is 1 meter RMSE. This accuracy specification was not tested explicitly during quality assessment procedures. Horizontal accuracy is indirectly evaluated during Vertical Accuracy evaluation. However no direct vertical accuracy check was performed on the Last Return data.
Vertical Accuracy specifications are stated for the bare-earth digital ground model data, not the last return data. During quality assessment the relationship between the last return, first return and the bare-earth (dgm) was investigated for a large set of random points across each delivery, to look for any systemic issues in inverted vertical surface separation.
Last return elevation data in ASCII format will be available for the entire ESA/SAO project area. Last return elevation data is not available for the Puget Sound LiDAR Consortium portion of King County.
Each easting/northing coordinate location has an elevation value.
Are there legal restrictions on access or use of the data?
- Access_Constraints:
- Certain processing and data handling charges for necessary cost recovery may apply to obtaining this data. Access to raw mass point files is by special request and request evaluation only.
- Use_Constraints:
- Users should recognize that Last Return data delivered by the vendor as randomly-spaced ASCII elevation files were minimally inspected for completeness and continuity. The bare-earth model derived from the last-return received more complete evaluation.
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 Last Return Elevation Data ASCII format, 'tile_abb'_dlmkc.asc
King County disclaims any warranty of use of any digital product or data beyond that for which it was designed.
| Data format: | ASCII text file |
|---|---|
| Network links: |
\\gisdw\kclib\plibrary3\idxp7500\dlm_ascii |
| 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