LiDAR Return Intensity Data

Frequently-anticipated questions:

• What does this data set describe?
  1. How should this data set be cited?
  2. What geographic area does the data set cover?
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
  5. What is the general form of this data set?
  6. How does the data set represent geographic features?
  7. How does the data set describe geographic features?
• Who produced the data set?
  1. Who are the originators of the data set?
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
• Why was the data set created?
• How was the data set created?
  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
  3. What similar or related data should the user be aware of?
• How reliable are the data; what problems remain in the data set?
  1. How well have the observations been checked?
  2. How accurate are the geographic locations?
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
  5. How consistent are the relationships among the data, including topology?
• How can someone get a copy of the data set?
  1. Are there legal restrictions on access or use of the data?
  2. Who distributes the data?
  3. What's the catalog number I need to order this data set?
  4. What legal disclaimers am I supposed to read?
  5. How can I download or order the data?
• Who wrote the metadata?

Title: LiDAR Return Intensity Data

Abstract:

LiDAR return intensity value data obtained from both the first LiDAR return and from the last LiDAR return, provided in separate files.Data is available as histogram-balanced TIFF 8-bit single-band image. Image data is orthorectified being tied to the LiDAR elevation return values and provided in the King County township-range (idxptrmbr) tile scheme as TxxRxx_fri003, and TxxRxx_lri003 for first-return intensity (fri) and last-return intensity (lri) imagery, respectively. The 003 represents the approximate resolution of the imagery, in feet, rounded from the actual GSD of 1 meter. The image data is also available as JP2000 compressed jp2 files. The intensity data is also available in ASCII format as variably-spaced points with easting,northing, and intensity-value. ASCII format data is will be available only for the King County project area of the County, as intensity data was not delivered under for the PSLC project area.

Supplemental_Information:

The image format of the intensity data is provided in the standard King County township-range (idxptrmbr) tiling scheme, 7500 (idxp7500) tiling scheme, as well as zone and region mosaics. Intensity data as ASCII files is tiled at the 7500 (idxp7500) tiling scheme only.

1. How should this data set be cited?

   County, King, 200307, LiDAR Return Intensity Data: King County, King County, WA.

   Online Links:

   • None

   Other_Citation_Details:

   This product is derived from LiDAR data from the King County ESA/SAO (Endangered Species Act/Sensitive Areas Ordinance) project. Intensity data was not obtained for LiDAR data collected for the Puget Sound LiDAR Consortium project area.

2. What geographic area does the data set cover?

   West_Bounding_Coordinate: -121.500000

   East_Bounding_Coordinate: -121.100000

   North_Bounding_Coordinate: +47.800000

   South_Bounding_Coordinate: +47.100000

3. What does it look like?

4. Does the data set describe conditions during a particular time period?

   Beginning_Date: Nov-2000

   Ending_Date: Feb-2003

   Currentness_Reference: Ground condition

5. What is the general form of this data set?

   Geospatial_Data_Presentation_Form: Raster Digital Data, Tabular Digital Data

6. How does the data set represent geographic features?
   1. How are geographic features stored in the data set?

      Indirect_Spatial_Reference:

      The intensity image data is organized in a standardized tile scheme. The highest resolution tiles are provided in a tiles that approximate the PLSS township-range grid for the project area. The tiles are defined by a minimum bounding rectangle (MBR) defined around each township-range, and identified by the township number as t## cocanenated with the range number as r##. A resulting representative tile_id would be t22r04.

      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).

      The ASCII data is provided in a standardized tiling scheme based on a 7500x7500 foot Stateplane grid in column-row format. Tiles are identified as ab01,ab02,....az01,az02....ba01,ba02...

      This is a Raster data set. It contains the following raster data types:
      • Dimensions 10546 x 10424, type Pixel

   2. What coordinate system is used to represent geographic features?

      Grid_Coordinate_System_Name: State Plane Coordinate System 1983

      State_Plane_Coordinate_System:

      SPCS_Zone_Identifier: Washington, North

      Lambert_Conformal_Conic:

      Standard_Parallel: 47.500000

      Standard_Parallel: 48.733333

      Longitude_of_Central_Meridian: -120.833333

      Latitude_of_Projection_Origin: 47.000000

      False_Easting: 1640416.666500

      False_Northing: 0.000000

      Planar coordinates are encoded using Row and column
      Abscissae (x-coordinates) are specified to the nearest 1
      Ordinates (y-coordinates) are specified to the nearest 1
      Planar coordinates are specified in Meters

      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.
      

7. How does the data set describe geographic features?

   Entity_and_Attribute_Overview:

   The image data has no attribution. It is provided in TIF with world file and JP2 formats. The ASCII format of the data is provided in 7500x7500 tiles comprised of randomly-spaced, comma/space delimited files of easting,northing,intensity-value, without a header.

   Entity_and_Attribute_Detail_Citation: Not applicable

1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
   • King County

2. Who also contributed to the data set?

3. To whom should users address questions about the data?

   Michael Leathers
   King County Geographic Information Center,
   GIS Data Coordinator
   201 S Jackson St, Suite 706
   Seattle, WA 98104
   USA
   

   206-263-4867 (voice)
   

In its TIFF format the intensity information provides a panchromatic image of the return surface at the 1-meter GSD (ground sample distance)/pixel resolution. Intensity values vary depending from which type of surface the LiDAR reflection is obtained and this translates into a series of tonal differences. In its balanced image format the data serves mainly as a backdrop providing some reference to current ground surface vegetative state at the time of LiDAR acquisition, though does not provide the same level of detail or definition that a true panchromatic orthophoto would at the same resolution.The ASCII intensity value data may provide a more detailed, unsmoothed/unbalanced description of the reflected surface. The intensity values have easting and northing geographic coordinates for surface location correlation.

1. From what previous works were the data drawn?

   3di (source 1 of 1)

   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.

   Other_Citation_Details:

   The King County ESA/SAO project is comprised of two separate project areas (phases). Phase I (lowland phase) includes the portion of western King County and southern Snohomish County that completes that portion of the County not covered by the PSLC project. The second phase (upland phase) includes the remainder of the County.

   Type_of_Source_Media:

   CD-R and DVD+R x,y,intensity_value records and GeoTIFF intensity value images.

   Source_Contribution:

   First and last return intensity data in ASCII format and GeoTIFF image format.

2. How were the data generated, processed, and modified?

   Date: 2002 (process 1 of 8)

   Vendor (Intensity) Production Step 1:

   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.

   Date: 2002 (process 2 of 8)

   Vendor (Intensity) Production Step 2:

   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.

   Date: 2002 (process 3 of 8)

   Vendor Production Step 3:

   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.

   Date: 2002 (process 4 of 8)

   Vendor (Intensity) Production Step 4:

   First and last return intensity point data was transferred to media for delivery to client in a comma/space delimited ASCII file of format easting,northing,intensity-value. Image format was generated through histogram-equalization of the variably-spaced points and conversion to GeoTIFF format, with world file.

   Date: 2002 (process 5 of 8)

   King County (Intensity) Production Step 1:

   After receipt and logging of media, the GeoTIFF images were transferred to on-line access location. ArcInfo 7.x operating on a Unix platform was used to convert each TIFF image to a grid using the IMAGEGRID command. The grids were merged to create a single composite grid for each delivery. GRIDIMAGE was used to convert the grid to a TIFF for quality evaluation and continuity check.

   Date: 2003 (process 6 of 8)

   King County (Intensity) Production Step 2:

   The individual delivery grids were mosaiced using GRID MERGE to create contiguous grids. Areas that did not have intensity values to the full extent of the tiles of idxptrmbr index were filled with 255 value background. The composite grids were clipped using GRID GRIDCLIP to the extents of their respective tiles. PROJECTDEFINE define the projection header and GRIDIMAGE was used to convert the GRID tiles to TIFF with world file.

   Date: 2003 (process 7 of 8)

   King County (Intensity) Production Step 3:

   The output TIFF images were compressed to jp2 format using JPG2000 compression software with a compression ratio of 5. This was done to minimize storage space requirements while preserving the data as lossless.

   Date: Jun-2004 (process 8 of 8)

   Tiling of ASCII data to standard KC 7500 scheme

   ASCII data as delivered by vendor was tiled in an approximate 1km x 1km tiling scheme based on a vendor UTM-based grid. The ASCII data was not reformatted but only retiled to KC standard scheme based on Stateplane 7500 ft x 7500 ft grid.

   From original vendor index, vendor tiles required for new 7500 tile were identified. Data files were awked to add a constant value of 1 into a lead column followed by remaining original x, y, intensity-value columns.

   All awked files were cocantenated into single file and submitted to ArcInfo command-line CREATETIN command with zero (0) filtering (weed) tolerance and bound arguement of subject 7500 tile.

   Created TIN was ungenerated to point coverage using TINARC command and coordinate values were assigned to each point using the ADDXY command. In TABLES, coverage was selected and X-coord, Y-coord and SPOT value (intensity value) were unloaded to 'tile-name'kc_lri.asc and 'tile-name'kc_fri.asc, for last-return and first-return data, respectively.

   Even with zero filtering tolerance, some points were dropped during the TIN process though the lost points is considered insignificant.

   For quality control, the TIN was converted to a lattice using the TINLATTICE command and a hillshade created using the HILLSHADE command. The hillshade grid was converted to a tif image using the GRIDIMAGE command and was inspected for general quality and tile bound consistency.

   Retiled ASCII point files were compressed using a zip compressing routine and stored in the Spatial Data Warehouse.

3. What similar or related data should the user be aware of?

1. How well have the observations been checked?

   The vendor has not supplied any accuracy report for the intensity data values, nor did King County evaluate the intensity values beyond a visual check for general consistency and quality.

2. How accurate are the geographic locations?

   Horizontal accuracy of the Intensity data was not tested explicitly. There no NMAS nor NSSDA accuracy statement is provided with the data. Horizontal accuracy is measured only as a function of the vertical accuracy of the LiDAR elevation data. The Intensity imagery appears to conflate consistently with the LiDAR data. Comparison to other orthoimagery the Intensity imagery is believed to be accurate to plus/minus 3 feet.

3. How accurate are the heights or depths?

   Not applicable

4. Where are the gaps in the data? What is missing?

   Intensity data, both in GEOTIFF image format and ASCII format will be available for the entire ESA/SAO project area. Intensity data is not available for the Puget Sound LiDAR Consortium portion of King County.

5. How consistent are the relationships among the observations, including topology?

   The ASCII data is variably-spaced and does not have a direct correlation to the pixel values in the image format. Further the ASCII values for the intensity data are stored in separate files than the ASCII elevation data files without any key relationship so any correlation between intensity and elevation must be done on a spatial coincidence. All x,y locations in the ASCII records do contain an intensity 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:

The intensity imagery and ASCII files are considered an important, yet secondary, product to the primary elevation models obtained from the project. The imagery, though having similarities to panchromatic orthophotography, does not provide the level of tonal difference resolution that true visible spectrum photography will provide. The intensity imagery and ASCII files are intended for integrated use with the LiDAR elevation model data rather than as purely stand-alone products.

1. Who distributes the data set? (Distributor 1 of 1)

   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)
   

2. What's the catalog number I need to order this data set?

   LiDAR First Return Intensity data TIFF format, LiDAR First Return Intensity data ASCII format, LiDAR Last Return Intensity data TIFF format, LiDAR Last Return Intensity data ASCII format,

3. What legal disclaimers am I supposed to read?

   King County disclaims any warranty of use of any digital product or data beyond that for which it was designed.

4. How can I download or order the data?
   • Availability in digital form:

     Data format:	TIF, JP2, ASCII
     Network links:	\\gisdw\kclib\plibrary3\idxptrmbr\intensity_firstret (jp2 image data) \\gisdw\kclib\plibrary3\idxptrmbr\intensity_lastret (jp2 image data) \\gisdw\kclib\plibrary3\idxp7500\intensity_firstret (tif image data) \\gisdw\kclib\plibrary3\idxp7500\intensity_lastret (tif image data) \\gisdw\kclib\plibrary3\idxp7500\lri_ascii (ASCII data) \\gisdw\kclib\plibrary3\idxp7500\fri_ascii (ASCII data)
     Media you can order:	CD-R, DVD+R (format CD: Read-only, DVD: DVD+R read-only)

   • Cost to order the data:

     Contact KCGIS Client Services <http://www.metrokc.gov/gis/services/> for cost of reproduction and delivery

Dates:

Last modified: 15-Jul-2003

Metadata author:

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

Metadata standard:

FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)