Geometry Type: Raster (TIF)
Table of Contents
1. Identification
2. Data Quality and Specifications
3. Attribute Information
| Purpose | The hydro-enforced digial elevation model may be used for hydologic modeling and identifying where water may collect. Since elevation values are modified due to placement of culverts, this model should not be used for creating contours or deriving elevation values. |
| Description | The bare earth digital elevation model (DEM) represents the earth's surface with all vegetation and anthropogenic features removed. It is derived from Green and NIR LiDAR data using TIN processing of the ground and bathymetric bottom point returns. Green LiDAR was used within the water’s edge breakline for data splicing shape (provided as another deliverable) only " and NIR LiDAR was used everywhere else outside of this shape. Within the NIR-only portion of the AOI all rivers greater than 20 feet in width and lakes at least 0.25 acres in size have been flattened to consistent elevations. Some smaller streams and ponds were also flattened when deemed appropriate. Water boundary polygons were developed manually and by using automatic algorithms. Elevation values were then assigned to the water's edge from the LiDAR data creating 3D breaklines enforced during model creation to flatten water bodies. Within the green-only portion of the AOI (inside the low tide breaklines shape), the data has been clipped to avoid triangulation and false interpolation over areas identified as voids in the Bathymetric Coverage Polygon (provided as a separate deliverable). Additionally, hydro-enforcement breaklines were created at all artificial obstructions to flow found in the ground model (i.e. culverts) to break the obstruction and allow flow to continue. Some elevation values have been interpolated across areas in the ground model where there is no elevation data (e.g. under dense vegetation). This version of hydroenforced DEM has not had sinks filled. Another version of hydroenforced DEM has been provided with sinks filled. The horizontal datum for this dataset is NAD83, the vertical datum is NAVD88, Geoid 12B, and the data is projected in New York State Plane - Long Island. Units are in US Survey Feet. Quantum Spatial collected the New York City LiDAR data for The City of New York between 05/03/17 and 07/26/17. |
| Source(s) | City of New York, Quantum Spatial Inc. |
| Publication Dates | Data: 2017 Last Update: 2018 Metadata: 09/12/2018 Update Frequency: As needed. This dataset was created as part of the 2017 LiDAR update |
| Available Formats | Topographic Mosaic Topographic Tiled Bathymetric Mosaic Bathymetric Tiled Topobathymetric Mosaic Topobathymetric Tiled |
| Use Limitations | |
| Access Rights | Public |
| Links | Digital Elevation and Surface Models available via New York State GIS Clearinghouse |
| Tags | LiDAR, Light Detection and Ranging, elevation data, topography, bare earth, hydro-flattened, hydro-enforced, breaklines, DEM, digital elevation model, New York City, New York, NYC, Manhattan, Brooklyn, Queens, The Bronx, Staten Island |
| Horizontal Coordinate System | New York State Plane Coordinates, Long Island East Zone, NAD83, US foot |
| Resolution | 1 foot |
| Spatial Coverage | New York City, NY |
| Temporal Coverage | Topographic: 05/03/2017 - 05/17/2017 Bathymetric: 07/04/2017 - 07/26/2017 |
| Capture and Update Notes | In some areas of heavy vegetation or forest cover, there may be relatively few ground points in the LiDAR data. TINing the points produces large triangles and hence the elevations may be less accurate within such areas. Due to some very large buildings within the city, there are very large triangles/interpolation throughout. Mosaicking lines and "cross hairs" may be seen in the middle of some interpolation. This is normal and will not affect the quality of the data. Wooden boardwalks and concrete boardwalks which are known to be on pylons and where separation is clearly visible, were removed from the bare earth models. In some areas of the dataset, the DEM goes from being hydroflattened to being bathymetric bottom data. This happens where the "Waters_Edge_for_Data_Splicing" shape cuts through a coastline or long stream/river. For ponds and lakes that cross this boundary, the data has been hydroflattened within the shape while bathymetric data may still exists within the LiDAR point cloud. |