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Standardized Breakline Delivery

By NGP Standards and Specifications

The current requirements in the Lidar Base Specification allow for delivery in different formats. A new, standardized breakline delivery format will allow automated checking of downstream constraints on centerline vertices and lake/pond values.  

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Introduction

The current version of the Lidar Base Specification (LBS 2023 rev. A) requires delivery of breaklines in a shapefile or geodatabase format without details regarding attribution. The new requirement has breaklines delivered in a GeoPackage format and includes more details regarding attribution and adds a centerline requirement. 

Current requirement:

In LBS 2023 rev. A: Breaklines:
Breaklines 
  • Delivery of all breaklines collected on or used in support of the project is required for USGS–NGP lidar projects. This includes breaklines used for bridge and saddle treatments and any additional breaklines required by project cooperators.
  • Breaklines representing all hydro-flattened features in a project, regardless of the method used for hydro-flattening, are required for USGS–NGP lidar projects. Specific research projects may be exempt from these requirements with prior approval of the USGS–NGP.
  • Breakline deliverables shall include or conform to the following procedures and specifications:
    • Breaklines developed to the limit of the DPA. 
    • Breaklines delivered in shapefile or file geodatabase formats, as PolylineZ and PolygonZ feature classes, as appropriate to the type of feature represented and the methodology used by the data producer. 
    • Breakline data shall be in the same CRS as the lidar data. 
    • Each breakline feature class shall have properly formatted, accurate, and complete georeferenced information stored in the format’s standard file system location. Each shapefile shall include a correct and properly formatted .prj file. All CRS information for 3-dimensional (3D) data shall include the vertical reference and identify the geoid model used to convert from the ellipsoid to orthometric heights. 
    • Breakline delivery may be in a single layer or in tiles, at the discretion of the data producer. In the case of tiled deliveries, all features shall edge-match exactly across tile boundaries in both the horizontal (x, y) and vertical (z) spatial dimensions. Delivered data shall be sufficient for the USGS to effectively recreate the delivered DEMs using the lidar points and breaklines without substantial editing.

The current requirement will be replaced with:

Breaklines 
  • Delivery of all breaklines collected on or used in support of the project is required for USGS–NGP lidar projects. This includes breaklines used for bridge and saddle treatments and any additional breaklines required by project cooperators.
  • Breaklines representing all hydro-flattened features in a project, regardless of the method used for hydroflattening, are required for USGS–NGP lidar projects. Specific research projects may be exempt from these requirements with prior approval of the USGS–NGP.
  • Work unit breaklines shall be delivered in the GeoPackage (GPKG) file format with the following requirements. 
    • The GPKG will use the most recent published version of the GeoPackage Encoding Standard (presently OGC GeoPackage Encoding Standard (2021)) will be used. A blank template will be provided.    
    • The GPKG will include all breaklines used to generate DEM products.
    • Streams and rivers, as defined in the hydroflattening section of this specification, shall contain a centerline with z-values corresponding to the hydroflattened surface.
    • The GPKG shall be in the same CRS as the lidar point cloud data. 
    • The CRS information of the GPKG shall adhere to all the Well-Known Text requirements in the Data Processing and Handling section of this specification, with only the following exceptions:  
    • The name of the GPKG shall contain only the USGS defined name of the work unit appended with “_Breaklines”; for example, FL_Everglades_2009_1_Breaklines).  
    • The GPKG shall have the following minimum attribution: 
      • unique_identifier (Text format) – Unique identifier that distinguishes the specific feature from all other features within the file. 
    • The GPKG will contain up to six layers. 
      • Waterbodies (polygon) 
      • Rivers (polygon)  
      • Centerline (line)  
      • Ocean (polygon)  
      • Other Breaklines Lines (line) 
      • Other Breaklines Polygons (polygon) 
    • If the project or work unit does not require one of the layers, such as Ocean, the contractors will not need to supply that layer.  
    • Other Breaklines Lines: used for bridges, buildings, dams, waterfall, for example.  
    • Other Breaklines Polygons: used for islands (unless depicted as holes within water polygons), bridges, buildings, dams, waterfalls, for example.  
    • All features shall be Z- and M-value enabled.