New York Office of Information Technology Services
Unpublished Material
Southwest 17-B - Fall, New York Lidar; Hydrologic Breaklines
vector data
Product: Hydrologic Breaklines.
Geographic Extent: Cattaraugus, Allegany, Genesee and Wyoming County, New York, covering approximately 2,185 square miles.
Dataset Description: Cattaraugus, Allegany, Genesee and Wyoming County, New York 2017 Lidar project called for the Planning, Acquisition, processing and derivative products of lidar data to be collected at a nominal pulse spacing (NPS) of 0.7 meter. Project specifications are based on the U.S. Geological Survey National Geospatial Program Base Lidar Specification, Version 1.2. The data was developed based on a horizontal projection/datum of NAD83(2011), Universal Transverse Mercator Zone 17 N, meters and vertical datum of NAVD88 (GEOID12B), meters. Lidar data was delivered as flightline-extent unclassified LAS swaths, as processed Classified LAS 1.4 files, formatted to 2,515 individual 1500 m x 1500 m tiles, as tiled bare earth DEMs; all tiled to the same 1500 m x 1500 m schema.
Ground Conditions: Lidar was collected in late 2017 and reflights early 2018, while no snow was on the ground and rivers were at or below normal levels. In order to post process the lidar data to meet task order specifications and meet ASPRS vertical accuracy guidelines, New York Office of Information Technology Services established a total of 17 ground control points that were used to calibrate the lidar to known ground locations established throughout the Cattaraugus, Allegany, Genesee and Wyoming County, New York project area. An additional 139 independent accuracy checkpoints, 77 in Bare Earth and Urban landcovers (77 NVA points). 62 in Tall Grass and Brushland/Low Trees categories (62 VVA points) were used to assess the vertical accuracy of the data. These checkpoints were not used to calibrate or post process the data.
To acquire detailed surface elevation data for use in conservation planning, design, research, floodplain mapping, dam safety assessments and elevation modeling, etc. Classified LAS files are used to show the manually reviewed bare earth surface. This allows the user to create Breaklines and Raster DEM. The purpose of these lidar data was to produce high accuracy 3D hydro-flattened Digital Elevation Model (DEM) with a 1 meter cell size. These raw lidar point cloud data were used to create classified lidar LAS files,3D breaklines, and hydro-flattened DEMs as necessary.
Breakline File Type = SHP
Breakline Elevation Units = Meters
Downhill Treatment Applied = Monotonic
Type of Hydro Treatment Required = Hydro-flattened
20171115
20180422
ground condition
None planned
-78.763149
-77.841087
43.002889
41.970881
None
Breaklines
Elevation Data
Lidar
None
New York
Wyoming County
Cattaraugus County
Genesee County
Allegany County
No restrictions apply to these 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 the limitations of the data. Acknowledgement of New York Office of Information Technology Services would be appreciated for products derived from these data. The data represented is the result of data collection and processing per contract specifications and indicates the general existing conditions at the time of the data collection. As such, it is only valid for its intended use, content, time, and accuracy specifications. The user is responsible for the results of any application of the data for other than its intended purpose.
Data covers the entire area specified for this project. Breaklines were collected in all inland ponds and lakes ~2 acres or greater. These features were flat and level water bodies at a single elevation for each vertex along the bank. The entire water surface edge is at or below the immediate surrounding terrain. Breaklines were collected for all streams and rivers ~30m nominal width or wider. These features are flat and level bank to bank, gradient will follow the surrounding terrain and the water surface will be at or below the surrounding terrain. Streams/river channels will break at culvert locations however not at elevated bridge locations. Partially elevated water bodies may be present where use of Class 10 (Ignored Ground) next to the hydro breaklines has eliminated ground points on a small berm or raised bank.
All files are inspected to ensure that they conform to the specified file naming conventions, all files load in their correct geographic position, all files conform to the project specifications for file standard and content. Points with extreme elevations (negative values, or positive values well above the expected maximum) are present in this dataset. These points are classified as low or high noise in classified point cloud tiles.
Hydro Flattening Breakline Processing: The Class 2 (ground) lidar points was used to collect 3D breaklines of inland streams and rivers with a 30 meter nominal width and Inland Ponds and Lakes of 2 acres or greater surface area. Elevation values were assigned to all Inland Ponds and Lakes, Inland Pond and Lake Islands, Inland Stream and River Islands, using TerraModeler functionality. All ground (ASPRS Class 2) lidar data inside of the collected inland breaklines were then classified to water (ASPRS Class 9) using TerraScan macro functionality. A buffer of 1 meter was also used around each hydro-flattened feature. These points were moved from ground (ASPRS Class 2) to Ignored Ground (ASPRS Class 10). Breaklines are reviewed against lidar intensity imagery to verify completeness of capture. All breaklines are then compared to TINs (triangular irregular networks) 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 proprietary tools. Partially elevated water bodies may be present where use of Class 10 (Ignored Ground) next to the hydro breaklines has eliminated ground points on a small berm or raised bank.
2018
Vector
Universal Transverse Mercator
17
0.9996
-81.00
0.0
500000
0.0
coordinate pair
0.01
0.01
meters
North American Datum of 1983 (2011)
Geodetic Reference System 80
6378137
298.257222101
North American Vertical Datum of 1988 (Geoid12B)
0.01
meters
Explicit elevation coordinate included with horizontal coordinates
20180823
New York Office of Information Technology Services
mailing and physical
10B Airline Drive
Albany
NY
12235
USA
(518)242-5061
FGDC Content Standard for Digital Geospatial Metadata
FGDC-STD-001-1998