U.S. Geological Survey
201601
Unknown
Ponds_and_Lakes
vector digital data
Leading Edge Geomatics (LEG) collected 994 square miles in the Virginia counties of Accomack and Northampton. The nominal pulse spacing for this project was 1 point every 0.7 meters. Dewberry used proprietary procedures to classify the LAS according to project specifications: 0-Never Classified, 1-Unclassified, 2-Ground (bare earth points identified as Model Key Points are flagged with the Model Key Point bit), 7-Low Noise, 9-Water, 10-Ignored Ground due to breakline proximity, 17- Bridge Decks, 18-High Noise. Dewberry produced 3D breaklines and combined these with the final LiDAR data to produce seamless hydro flattened DEMs for the project area. The data was formatted according to the VBMP tile naming convention with each tile covering an area of 5,000 feet by 5,000 ft. A total of 1375 LAS tiles and 1310 DEM tiles were produced for the entire project.
The purpose of this LiDAR data was to produce high accuracy 3D elevation products, including tiled LiDAR in LAS 1.4 format, 3D breaklines, and 2.5 foot cell size hydro flattened Digital Elevation Models (DEMs). All products follow and comply with USGS Lidar Base Specification Version 1.2.
A complete description of this dataset is available in the Final Project Report submitted to the U.S. Geological Survey.
20150411
20150424
ground condition
As needed
-76.093949
-75.227100
38.064707
37.062181
None
DTM
Elevation
Lidar
LAS
DEM
Hydro Flattened
Breaklines
Bare Earth
None
Virginia
Eastern Shores
Accomack County
Northampton County
USA
None
This data was produced for the U.S. Geological Survey according to specific project requirements. This information is provided "as is". Further documentation of this data can be obtained by contacting: USGS NGTOC, 1400 Independence Road, Rolla, MO 65401. Telephone (573) 308-3810.
U.S. Geological Survey
Program Manager
mailing and physical address
1400 Independence Road
Rolla
MO
65401
USA
(573) 308-3810
pemmett@usgs.gov
Microsoft Windows 7 Enterprise Service Pack 1; ESRI ArcCatalog 10.3
Data covers the tile scheme provided for the project area.
A visual qualitative assessment was performed to ensure data completeness against the intensity images derived from Lidar points.
Breaklines compiled using Lidargrammetry. Breakline placement is compared to LiDAR intensity imagery and terrain models to ensure accurate breakline horizontal placement relative to the source LiDAR. However, absolute horizontal accuracy is not assessed on the breaklines.
Only checkpoints photo-identifiable in the intensity imagery can be used to test the horizontal accuracy of the LiDAR. Photo-identifiable checkpoints in intensity imagery typically include checkpoints located at the ends of paint stripes on concrete or asphalt surfaces or checkpoints located at 90 degree corners of different reflectivity, e.g. a sidewalk corner adjoining a grass surface. The xy coordinates of checkpoints, as defined in the intensity imagery, are compared to surveyed xy coordinates for each photo-identifiable checkpoint. These differences are used to compute the tested horizontal accuracy of the LiDAR. As not all projects contain photo-identifiable checkpoints, the horizontal accuracy of the LiDAR cannot always be tested.
2.13 ft (65 cm)
Dewberry does not perform independent horizontal accuracy testing on the breaklines. Breaklines compiled using Lidargrammetry.
Lidar vendors calibrate their lidar systems during installation of the system and then again for every project acquired. Typical calibrations include cross flights that capture features from multiple directions that allow adjustments to be performed so that the captured features are consistent between all swaths and cross flights from all directions.
Dewberry tested the horizontal accuracy of the LiDAR by comparing photo-identifiable survey checkpoints to the LiDAR Intensity Imagery. As only seventeen (17) checkpoints were photo-identifiable, the results are not statistically significant enough to report as a final tested value but the results of this testing are shown below.
Using NSSDA methodology (endorsed by the ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014)), horizontal accuracy at the 95% confidence level (called ACCURACYr) is computed by the formula RMSEr * 1.7308 or RMSExy * 2.448. Actual positional accuracy of this dataset was found to be RMSEx = 0.83 ft (25 cm) and RMSEy = 0.91 ft (28 cm) which equates to +/- 2.13 ft (65 cm) at 95% confidence level.
Breaklines compiled using Lidargrammetry. Breakline elevations are compared to LiDAR elevations to ensure accurate breakline elevations relative to the LiDAR. However, absolute vertical accuracy of the breaklines is not tested.
The vertical accuracy of the LiDAR was tested by Dewberry with 113 independent survey checkpoints. The survey checkpoints are evenly distributed throughout the project area and are located in areas of non-vegetated terrain (61 checkpoints), including bare earth, open terrain, and urban terrain, and vegetated terrain (52 checkpoints), including forest, brush, tall weeds, crops, and high grass. The vertical accuracy is tested by comparing survey checkpoints to a triangulated irregular network (TIN) that is created from the LiDAR ground points. Checkpoints are always compared to interpolated surfaces created from the LiDAR point cloud because it is unlikely that a survey checkpoint will be located at the location of a discrete LiDAR point.
All checkpoints located in non-vegetated terrain were used to compute the Non-vegetated Vertical Accuracy (NVA). Project specifications required a NVA of 0.64 ft (19.6 cm) at the 95% confidence level based on RMSEz (0.33 ft/10 cm) x 1.9600. All checkpoints located in vegetated terrain were used to compute the Vegetated Vertical Accuracy (VVA). Project specifications required a VVA of 0.96 ft (29.4 cm) based on the 95th percentile.
0.41 ft (12.5 cm)
Breaklines compiled using Lidargrammetry. Breakline elevations are compared to LiDAR elevations to ensure accurate breakline elevations relative to the LiDAR. However, absolute vertical accuracy of the breaklines is not tested.
This LiDAR dataset was tested to meet ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014) for a 0.33 ft (10 cm) RMSEz Vertical Accuracy Class. Actual NVA accuracy was found to be RMSEz =0.21 ft (6.40 cm), equating to +/- 0.41 ft (12.5 cm) at 95% confidence level.
0.58 ft (17.7 cm)
Breaklines compiled using Lidargrammetry. Breakline elevations are compared to LiDAR elevations to ensure accurate breakline elevations relative to the LiDAR. However, absolute vertical accuracy of the breaklines is not tested.
This LiDAR dataset was tested to meet ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014) for a 0.33 ft (10 cm) RMSEz Vertical Accuracy Class. Actual VVA accuracy was found to be +/- 0.58 ft (17.7 cm) at the 95th percentile.
The 5% outliers consisted of 3 checkpoints that are larger than the 95th percentile. These checkpoints have DZ values ranging between 0.60 ft (18.3 cm) and 0.88 ft (26.8 cm).
Data for the Eastern Shores Virginia QL2 LiDAR project was acquired by Leading Edge Geomatics (LEG).
The project area included approximately 994 contiguous square miles or 2574.45 square kilometers for the counties of Accomack and Northampton in Virginia. LiDAR sensor data were collected with the Riegl 680i LiDAR system. The data was delivered in the State Plane coordinate system, feet, Virginia South, horizontal datum NAD83, vertical datum NAVD88, Geoid 12a. Deliverables for the project included a raw (unclassified) calibrated LiDAR point cloud, survey control, and a final acquisition/calibration report.
The calibration process considered all errors inherent with the equipment including errors in GPS, IMU, and sensor specific parameters. Adjustments were made to achieve a flight line to flight line data match (relative calibration) and subsequently adjusted to control for absolute accuracy. Process steps to achieve this are as follows:
Rigorous LiDAR calibration: all sources of error such as the sensor's ranging and torsion parameters, atmospheric variables, GPS conditions, and IMU offsets were analyzed and removed to the highest level possible. This method addresses all errors, both vertical and horizontal in nature. Ranging, atmospheric variables, and GPS conditions affect the vertical position of the surface, whereas IMU offsets and torsion parameters affect the data horizontally. The horizontal accuracy is proven through repeatability: when the position of features remains constant no matter what direction the plane was flying and no matter where the feature is positioned within the swath, relative horizontal accuracy is achieved.
Absolute horizontal accuracy is achieved through the use of differential GPS with base lines shorter than 25 miles. The base station is set at a temporary monument that is 'tied-in' to the CORS network. The same position is used for every lift, ensuring that any errors in its position will affect all data equally and can therefore be removed equally.
Vertical accuracy is achieved through the adjustment to ground control survey points within the finished product. Although the base station has absolute vertical accuracy, adjustments to sensor parameters introduces vertical error that must be normalized in the final (mean) adjustment.
A copy of the final calibrated swaths are maintained in LAS format 1.2 for production utilizing Terrascan software. A second, identical version of final calibrated swaths are converted from v1.2 to v1.4 using GeoCue software. The withheld and overlap bits are set and all headers, appropriate point data records, and variable length records, including spatial reference information, are updated in GeoCue software and then verified using proprietary Dewberry tools.
Airborne Global Positioning System Data
Inertial Measurement Unit
201504
Calibrated LiDAR Point Cloud LAS 1.4 format
Leading Edge Geomatics
mailing and physical address
2384 Route 102 Highway
Lincoln
NB
E3B 7G1
Canada
506-446-4403
506-446-4402
Monday to Friday, 8 - 5
Dewberry utilizes a variety of software suites for inventory management, classification, and data processing. All LiDAR related processes begin by importing the data into the GeoCue task management software. The swath data is tiled according to project specifications (5,000 ft x 5,000 ft). Dewberry extended the client provided boundary where tiles had ground to include thirty four extra tiles. The tiled data is then opened in Terrascan where Dewberry classifies edge of flight line points that may be geometrically unusable to a separate class. These points are separated from the main point cloud so that they are not used in the ground algorithms. Dewberry then uses proprietary ground classification routines to remove any non-ground points and generate an accurate ground surface. The ground routine consists of three main parameters (building size, iteration angle, and iteration distance); by adjusting these parameters and running several iterations of this routine an initial ground surface is developed. The building size parameter sets a roaming window size. Each tile is loaded with neighboring points from adjacent tiles and the routine classifies the data section by section based on this roaming window size. The second most important parameter is the maximum terrain angle, which sets the highest allowed terrain angle within the model. As part of the ground routine, low noise points are classified to class 7 and high noise points are classified to class 18. Once the ground routine has been completed, bridge decks are classified to class 17 using bridge breaklines compiled by Dewberry. A manual quality control routine is then performed using hillshades, cross-sections, and profiles within the Terrasolid software suite. After this QC step, a peer review is performed on all tiles and a supervisor manual inspection is completed on a percentage of the classified tiles based on the project size and variability of the terrain. After the ground classification and bridge deck corrections are completed, the dataset is processed through a water classification routine that utilizes breaklines compiled by Dewberry to automatically classify hydrographic features. The water classification routine selects ground points within the breakline polygons and automatically classifies them as class 9, water. During this water classification routine, points that are within 1x NPS or less of the hydrographic features are moved to class 10, an ignored ground due to breakline proximity. Next, an intelligently thinned ground classification identified model key points and are flagged with the Model Key Point bit. Overage points are then identified in Terrascan and GeoCue is used to set the overlap bit for the overage points and the withheld bit is set on the withheld points previously identified in Terrascan before the ground classification routine was performed. A final QC is performed on the data. The LAS files are then converted from v1.2 to v1.4 using GeoCue software. At this time, all headers, appropriate point data records, and variable length records, including spatial reference information, are updated in GeoCue software and then verified using proprietary Dewberry tools.
The data was classified as follows:
Class 1 = Unclassified. This class includes vegetation, buildings, noise etc.
Class 2 = Ground (bare earth points identified as Model Key Points are flagged with the Model Key Point bit)
Class 7 = Low Noise
Class 9 = Water
Class 10 = Ignored Ground due to breakline proximity
Class 17 = Bridge Decks
Class 18 = High Noise
The LAS header information was verified to contain the following:
Class (Integer)
Adjusted GPS Time (0.0001 seconds)
Easting (0.003 m)
Northing (0.003 m)
Elevation (0.003 m)
Echo Number (Integer)
Echo (Integer)
Intensity (16 bit integer)
Flight Line (Integer)
Scan Angle (degree)
Calibrated LiDAR Point Cloud LAS 1.2 format
201509
Final Tiled LiDAR datasets in LAS 1.4 format
Elise MacPherson
Dewberry - Geospatial Services Group
Project Manager
mailing and physical address
1000 N. Ashley Drive, Suite 801
Tampa
FL
33602
USA
813.421.8647
813.225.1385
emacpherson@dewberry.com
8:00 - 5:00 EST
Existing lidar data acquired and processed as part of the NOAA Sandy Supplemental project were re-processed and combined with the LEG data to supplement/complete data coverage along the eastern portion of this project
Calibrated LiDAR Point Cloud LAS 1.2 format
201509
Final Tiled LiDAR datasets in LAS 1.4 format
Elise MacPherson
Dewberry - Geospatial Services Group
Project Manager
mailing and physical address
1000 N. Ashley Drive, Suite 801
Tampa
FL
33602
USA
813.421.8647
813.225.1385
emacpherson@dewberry.com
8:00 - 5:00 EST
Dewberry used GeoCue software to develop raster stereo models from the LiDAR intensity. The raster resolution was 2.5 feet.
Final Tiled LiDAR datasets
201509
Lidar Intensity Stereopairs
Elise MacPherson
Dewberry - Geospatial Services Group
Project Manager
mailing and physical address
1000 N. Ashley Drive, Suite 801
Tampa
FL
33602
USA
813.421.8647
813.225.1385
emacpherson@dewberry.com
8:00 - 5:00 EST
LiDAR intensity stereopairs were viewed in 3-D stereo using Socet Set for ArcGIS softcopy photogrammetric software. The breaklines are collected directly into an ArcGIS file geodatabase to ensure correct topology. The LiDARgrammetry was performed under the direct supervision of an ASPRS Certified Photogrammetrist. The breaklines were stereo-compiled in accordance with the Data Dictionary.
The data dictionary defines Inland Ponds and Lakes as a closed water body feature that is at a constant elevation. These polygon features should be collected at the land/water boundaries of constant elevation water bodies such as lakes, reservoirs, and ponds. Features shall be defined as closed polygons and contain an elevation value that reflects the best estimate of the water elevation at the time of data capture. Water body features will be captured for features 2 acres in size or greater. Donuts will exist where there are islands greater than 1 acre in size within a closed water body. Breaklines must be captured at or just below the elevations of the immediately surrounding terrain. Under no circumstances should a feature be elevated above surrounding LiDAR points. The compiler shall take care to ensure that the z-value remains consistent for all vertices placed on the water body.
Lidar Intensity Stereopairs
201511
3D breaklines
Elise MacPherson
Dewberry - Geospatial Services Group
Project Manager
mailing and physical address
1000 N. Ashley Drive, Suite 801
Tampa
FL
33602
USA
813.421.8347
813.225.1385
emacpherson@dewberry.com
8:00 - 5:00 EST
Breaklines are reviewed against LiDAR intensity imagery to verify completeness of capture. All breaklines are then compared to ESRI terrains created from ground only points prior to water classification. The horizontal placement of breaklines is compared to terrain features and the breakline elevations are compared to LiDAR elevations to ensure all breaklines match the LiDAR within acceptable tolerances. Some deviation is expected between breakline and LiDAR elevations due to monotonicity, connectivity, and flattening rules that are enforced on the breaklines. Once completeness, horizontal placement, and vertical variance is reviewed, all breaklines are reviewed for topological consistency and data integrity using a combination of ESRI Data Reviewer tools and proprietary tools. Corrections are performed within the QC workflow and re-validated.
3D breaklines
201511
Final 3D breaklines
Elise MacPherson
Dewberry - Geospatial Services Group
Project Manager
mailing and physical address
1000 N. Ashley Drive, Suite 801
Tampa
FL
33602
USA
813.421.8347
813.225.1385
emacpherson@dewberry.com
8:00 - 5:00 EST
Vector
G-polygon
437
Lambert Conformal Conic (State Plane Virginia South FIPS 4502)
36.766
37.966
-78.5
36.333
11482916.666
3280833.333
coordinate pair
0.000100
0.000100
U.S. survey feet
North American Datum of 1983(2011)
Geodetic Reference System 80
6378137.000000
298.257222
North American Vertical Datum of 1988 (Geoid 12A)
0.000100
U.S. survey feet
Explicit elevation coordinate included with horizontal coordinates
Inland_Lakes_Ponds
Waterbody polygon.
U.S. Geological Survey data dictionary
OBJECTID
Internal feature number.
ESRI
Sequential unique whole numbers that are automatically generated.
SHAPE
Feature geometry.
ESRI
Coordinates defining the features.
SHAPE_Length
Length of feature in internal units.
ESRI
Positive real numbers that are automatically generated.
SHAPE_Area
Area of feature in internal units squared.
ESRI
Positive real numbers that are automatically generated.
U.S. Geological Survey
Program Manager
mailing and physical address
1400 Independence Road
Rolla
MO
65401
USA
(573) 308-3810
pemmett@usgs.gov
Downloadable Data
This data was produced for the U.S. Geological Survey according to specific project requirements. This information is provided "as is". Further documentation of this data can be obtained by contacting: USGS, 1400 Independence Road, Rolla, MO 65401. Telephone (573) 308-3810.
201601
U.S. Geological Survey
Patrick Emmett
Program Manager
mailing and physical address
1400 Independence Road
Rolla
MO
65401
USA
(573) 308-3810
pemmett@usgs.gov
FGDC Content Standards for Digital Geospatial Metadata
FGDC-STD-001-1998
local time
http://www.esri.com/metadata/esriprof80.html
ESRI Metadata Profile