Fugro Geospatial. Inc.20180405District of Columbia 2018 LiDAR ProjectLidar point cloudThese lidar data are processed classified LAS 1.4 files at USGS QL2 covering the District of Columbia. Voids exist in the data due to data redaction conducted under the guidance of the United States Secret Service.This data is used for the planning and management of Washington, D.C. by local government agencies.USGS-NGP Base Specification v1.4ALS8050.72.0722956.561502044292Lidar_Pulse_Duration
.Lidar_Pulse_WidthLidar_Central_WavelengthLidar_Multiple_Pulses_In_AirLidar_Beam_DivergenceLidar_Swath_WidthLidar_Swath_OverlapGeoid12B00.027201.46Withheld (ignore) points were identified in these files using the standard LAS Withheld bitSwath "overage" points were identified in these files using the standard LAS overlap bit1Processed, but unclassified2Bare-earth ground3Low vegetation4Medium vegetation5High vegetation6Buildings7Low noise9Water17Bridge Decks18High noise20Ignored Ground2018040520180405ground conditionNone planned-77.122373 -76.90071639.00174638.785481NoneLiDARLAS Point CloudElevation Data2018NoneWashington DCNo restrictions apply to this data.None. However, users should be aware that temporal changes may have occurred since this dataset was collected and that some parts of these data may no longer represent actual surface conditions. Users should not use these data for critical applications without a full awareness of its limitations.Data covers the entire District of Columbia.Voids exist in the dataset as directed by the United States Secret Service (USSS).The lidar data acquisition for DC OCTO was flown to support the creation of a 2 ppsm classified lidar point cloud data set, 1m resolution hydro-flattened bare earth DEM and nDSM, and .6m contours over the full project area covering the District of Columbia. Due to security requirements in the area, Fugro received waivers to fly in the Flight Restricted Zone (FRZ) and P-56 areas.
The lidar acquisition was flown in a single lift on April 5, 2018, at an altitude of 9,700 feet above mean sea level and composed of 24 flight lines, 22 primary lines and two cross ties. All lidar data was collected with a Piper Navajo PA31-50, tail# N62912 and a Leica ALS80 lidar sensor, #133. Due to the known difficulties flying over DC, the ALS80 sensor was selected to take advantage of its flight altitude and speed, minimizing the number of lifts for the various flight restrictions. All lidar was collected in conjunction with airborne GPS.2018Wiles Mensch Corporation, under contract to Fugro Geospatial, Inc., successfully established ground
control for the DC OCTO project area. A total of 31 survey points were used, 6 ground control points, 20
NVA checkpoints, and 5 VVA checkpoints. GPS was used to establish the control network. The ground
control was delivered in Maryland State Plane (FIPS1900) meters, with the horizontal datum provided in
both NAD1983 and NAD83(2011). The vertical datum was the North American Vertical Datum of 1988
(NAVD88) using GEOID12B. Control was collected on April 5, 2018, several ground control points
required resurvey due to proximity to elevated structures, they were recollected on May 10, 2018 and are
designated with a -2. Because the ground control points and NVA checkpoints are collected to the same
specifications and to prevent a delay in processing, several NVA checkpoints were selected to be used
as ground control; following the resurvey the ground control points that needed resurvey were used as
NVA checkpoints. The table below shows which points were used as the control, which were used as
NVA checkpoints, and which were VVA checkpoints:
Control Points NVA Checkpoints VVA Checkpoints
GCP-02 GCP-01-2 NVA-09 VVA-01
GCP-03 GCP-04-2** NVA-10 VVA-02
NVA-01 GCP-05-2** NVA-11 VVA-03
NVA-08 GCP-06-2 NVA-12-2 VVA-04
NVA-13 NVA-02 NVA-14 VVA-05
NVA-16 NVA-03 NVA-15
NVA-04-2 NVA-17
NVA-05 NVA-18
NVA-06 NVA-19
NVA-07-2 NVA-20
During initial processing, QC and accuracy assessments were run the data in NAD83(2011) datum which
is the native coordinate system from the sensor. Following boresight the data was re-projected to NAD83
for delivery per the contract specifications and cut to the delivery extent the control was re-run in the final deliverable projection. After cutting to the deliverable extent, points GCP-04-2 and GCP-05-2 fell outside of the delivery footprint.2018Pre-Processing and Boresight
All lidar data went through a preliminary field review to ensure that complete coverage was obtained and
that there were no gaps between flight lines prior to leaving the project site. Once back in the office, the data went through a complete iteration of processing to ensure that it is complete, uncorrupted and that the entire project area was covered without gaps. There were three steps to processing: 1) GPS/IMU
processing - airborne GPS and IMU data was processed using the airport GPS base station data; 2) raw
lidar data processing - the raw data was processed to LAS format flight lines with full resolution output
before performing QC. A starting configuration file is used in this process, which contains the latest
calibration parameters for the sensor and outputs the flight line trajectories. 3) Verification of coverage
and data quality - the trajectory files were checked to ensure completeness of acquisition for the flight
lines, calibration lines and cross flight lines. Intensity images were generated for the entire lift and
thoroughly reviewed for data gaps in project area. A sample TIN surface was generated to ensure no
anomalies or turbulence were present in the data; if any adverse quality issues were discovered, the flight
line was rejected and re-flown. The achieved post spacing confirmed against the project specification of
2 ppsm and checked for clustering in point distribution. The review showed that the lidar data exceeded
the 2 ppsm post spacing.
The lidar data was boresighted using the following steps: 1) The raw data was processed to LAS format
flight lines using the final GPS/IMU solution. This LAS dataset was used as source data for boresighting.
2) Fugro proprietary and commercial software was used to calculate initial boresight adjustment angles
based on sample areas within the lift. These areas cover calibration flight lines collected in the lift, cross tie and production flight lines. These areas are well distributed in the lift coverage and cover multiple terrain types that are necessary for boresight angle calculation. The results were analyzed and any additional adjustments were completed the selected areas. 3) Once the boresight angle calculation was
completed, the adjusted settings were applied to the flight lines of the lift and checked for consistency.
The technicians utilized commercial and proprietary software packages to analyze the matching between
flight line overlaps for the entire lift and adjusted as necessary. 4) Vertical misalignment of all flight lines was checked and corrected, as was the matching between data and ground truth. 5) A final vertical
accuracy check of the boresighted flight lines against the surveyed ground control points was conducted.
The boresighted lidar data achieved a vertical accuracy of 0.027m RMSE (0.051m at 95% confidence)
against the 20 NVA checkpoint control locations (two of which fall outside of the deliverable project
boundary).2018Data Redaction
Following the boresight completion, the lidar dataset redaction was conducted under the guidance of the
United States Secret Service. All lidar data returns and collected data were removed from the dataset
based on the redaction footprint shapefile generated in 2017.2018Classified Point Cloud
The boresighted lidar data underwent an automated classification filter to classify low noise, high noise,
and ground points. To obtain optimum results, the parameters used by the automated classification filter
are customized for each terrain type and project. Once the automated filtering was completed, the lidar
files went through a visual inspection to ensure that an appropriate level of filtering was used. In cases
where the filtering was too aggressive and important terrain may have been filtered out, the data is either
run through a different filter within localized area or is corrected during the manual filtering process. A second automatic filter is run for the initial classification on buildings. Following the automatic filters, manual editing was completed in Terrascan software to correct any misclassification of the lidar dataset. All tiles then went through a peer review to ensure proper editing and consistency. When the peer review was completed two additional rounds of automatic filters were applied. The first filter ran the vegetation classification - moving the unclassified points to either the low, medium, or high vegetation classes. The second filter removed the cars on bridges, previously classified as vegetation, by buffering the bridges by two meters on each side (to maintain tree overhang on road shoulders and sidewalks) and then moving vegetation points over the center of the bridge to unclassified.
Once the manual inspection, QC, and auto filter is complete for the lidar tiles, the LAS point cloud data
was re-projected into the final deliverable projection and the accuracy statistics were re-run to confirm the deliverable accuracy. The LAS was then cut to the final delivery layout and in LAS 1.4 format for delivery. The point cloud was delivered with data in the following classifications: Class 1 - Processed but
Unclassified; Class 2 - Bare Earth Ground; Class 3 - Low Vegetation; Class 4 - Medium Vegetation; Class
5 - High Vegetation, Class 6 - Buildings; Class 7 - Low Point (Noise); Class 9 - Water; Class 17 - Bridge
Decks; Class 18 - High Noise; Class 20 - Ignored Ground.2018Point38.339.45-7737.66666666666674000000coordinate pair0.00010.0001metersNorth American Datum of 1983Geodetic Reference System 806378137298.257222101North American Vertical Datum of 1988 (GEOID12B)0.01metersExplicit elevation coordinate included with horizontal coordinates20170831D.C. Office of the Chief Technology OfficerGIS Data Coordinatormailing and physical200 I Street SE, 5th FloorWashingtonDC20003US859-277-8700(202) 727-5660dcgis@dc.gov8:30 AM to 5:00 PM (Eastern Time)FGDC Content Standard for Digital Geospatial MetadataFGDC-STD-001-1998None.None.None.UnclassifiedNone