| Processing Steps
- Acquisition. The LiDAR data was collected on October 28th, 2009, March 22, 2010 and
June 12th-16th, 2010. The survey used both the Leica ALS50 Pase II and ALS 60 laser
systems mounted in a Cessna Caravan 208. Near nadir scan angles were used to increase
penetration of vegetation to ground surfaces. Ground level GPS and aircraft IMU were
collected during the flight.
- 1. Flight lines and data were reviewed to ensure complete coverage of the study area
and positional accuracy of the laser points. 2. Laser point return coordinates were
computed using ALS Post Processor software, IPAS Pro GPS/INS software, and Waypoint
GPS, based on independent data from the LiDAR system, IMU, and aircraft. 3. The raw
LiDAR file was assembled into flight lines per return with each point having an associated
x, y, and z coordinate. 4. Visual inspection of swath to swath laser point consistencies
within the study area were used to perform manual refinements of system alignment.
5. Custom algorithms were designed to evaluate points between adjacent flight lines.
Automated system alignment was computed based upon randomly selected swath to swath
accuracy measurements that consider elevation, slope, and intensities. Specifically,
refinement in the combination of system pitch, roll and yaw offset parameters optimize
internal consistency. 6. Noise (e.g., pits and birds) was filtered using ALS postprocessing
software, based on known elevation ranges and included the removal of any cycle slips.
7. Using TerraScan and Microstation, ground classifications utilized custom settings
appropriate to the study area. 8. The corrected and filtered return points were compared
to the RTK ground survey points collected to verify the vertical and horizontal accuracies.
9. Points were output as laser points, TINed and GRIDed surfaces
- The NOAA Coastal Services Center (CSC) downloaded topographic files in text format
from PSLC's website. The files contained lidar easting, northing, elevation, intensity,
return number, class, scan angle and GPS time measurements. The data were received
in Washington State Plane South Zone 4601, NAD83 coordinates and were vertically referenced
to NAVD88 using the Geoid03 model. The vertical units of the data were feet. CSC performed
the following processing for data storage and Digital Coast provisioning purposes:
1. The All-Return ASCII txt files were parsed to LAS files. 2. The All-Return ASCII
files were converted from txt format to las format using LASTools' txt2las tool and
reclassified to fit the CSC class list, N=1 (unclassified), G=2 (ground). 3. The las
files were converted from orthometric (NAVD88) heights to ellipsoidal heights using
Geoid03. 4. The las files' vertical units were converted from feet to meters, removing
bad elevations. 5. The las files were converted from a Projected Coordinate System
(WA SP South) to a Geographic Coordinate system (NAD83) 6. The las files' horizontal
units were converted from feet to decimal degrees. 7. The data were converted to LAZ
- The NOAA National Geophysical Data Center (NGDC) received lidar data files via ftp
transfer from the NOAA Coastal Services Center. The data are currently
being served via NOAA CSC Digital Coast at http://www.csc.noaa.gov/digitalcoast/.
The data can be used to re-populate the system. The data are archived in LAS or LAZ
The LAS format is an industry standard for LiDAR data developed by the American Society
of Photogrammetry and Remote Sensing (ASPRS); LAZ is a loseless compressed version
LAS developed by Martin Isenburg (http://www.laszip.org/). The data are exclusively
in geographic coordinates (either NAD83 or ITRF94). The data are referenced vertically
the ellipsoid (either GRS80 or ITRF94), allowing for the ability to apply the most
up to date geoid model when transforming to orthometric heights.