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3D Elevation Program (3DEP) Vertical Accuracy Error Dictionary

By NGP Standards and Specifications

The purpose of this dictionary is to provide standardized language to describe commonly encountered errors associated with Light Detection and Ranging (lidar) survey points submitted to USGS Elevation Operations. This document is intended to improve communication between 3D Elevation Program operations, the project’s point of contact, contractors, contributors, and partners. Please note this list

Click here to download a .pdf of the VA Error Dictionary

For the purposes of this document, the term “Survey Point” refers to all checkpoints; Non-vegetative Vertical Accuracy (NVA), Vegetated Vertical Accuracy (VVA), Bathometric Vertical Accuracy (BVA) and control points delivered in accordance with the applicable USGS Lidar Base Specification (LBS) and ASPRS Positional Accuracy Standards for Digital Geospatial Data for review.

Table of Contents

Project Survey Points
  •   Erroneous Point
  •   Format
  •   Incorrect Attribution
    • unique identifier
    • point_type
    • comment
    • collection_date
    • source_geoid
    • source_horizontal_epsg
    • source_horizontal_unit
    • source_vertical_epsg
    • source_vertical_unit
    • source_easting
    • source_northing
    • source_elevation
    • project_id
  • Incorrect Geometry
    • Quantity
    • Spatial Distribution
    • Location
    • Z-Value
  • Spatial Reference

 

Content

  • Erroneous Point - Any errors involving placement of survey points not in accordance with the ASPRS Positional Accuracy Standards definitions as referenced by Lidar Base Specification. A survey point may be considered erroneous due to the properties of its physical location on the ground. Examples include, but are not limited to: 
    • Located on steep terrain with slopes greater than 10%.
    • Located on elevated surfaces not included in the Digital Elevation Model, such as a bridge or deck.
    • Located within a few meters of a breakline which significantly redefines the interpolation area surrounding the point.
    •  Located in areas where topography has changed significantly between the collection and final survey dates.

 

  • Format - Any errors involving the format of the digital file provided for Vertical Accuracy review. Examples include but are not limited to:
    • File not properly named in accordance with applicable Lidar Base Specification.
    • Delivered in incorrect file format (please refer to applicable Lidar Base Specification for requirements).
    • File is corrupt and will not load into GIS software.

 

  • Incorrect Attribution - Any errors involving content, existence, and/or format of the attribution of survey points delivered for review. General errors applicable to every attribute field include:
    • Field is missing completely from Geopackage.
    • Field is misspelled or named not in accordance with applicable Lidar Base Specification. (Note: the use of “metre” is an acceptable alternative to “meter.”)
    • Field is present, but not populated.
      • Errors specific to required attribute fields are detailed below:
        • unique_identifier - Field failed to contain single unique identifier for each specific point distinguishing a point from all others (i.e., two or more features share the same identifier), or identifiers are inconsistent with survey reports and/or images.
        • point_type - Field was populated with a value other than NVA, VVA, Control, or BVA.
        • comment - Additional information is inconsistent with similar information in survey reports and/or images.
        • collection_date - Date format is inconsistent with format specified in applicable Lidar Base Specification (i.e., date recorded as 3 May 2022 instead of 2022-05-03), and/or date associated with survey point(s) is inconsistent with survey reports and/or images.
        • source_geoid - Geoid model specified is inconsistent with the survey reports and/or images.
        • source_horizontal_epsg - Source horizontal EPSG specified is inconsistent with survey reports and/or images.
        • source_horizontal_unit - Source horizontal unit of measure specified is inconsistent with source unit described in horizontal EPSG or is populated with a unit other than those accepted by USGS (i.e., meter, US survey feet, or international feet).
        • source_vertical_epsg - Source vertical EPSG specified is inconsistent with survey reports or images.
        • source_vertical_unit - Source vertical unit of measure specified is inconsistent with source unit described in horizontal EPSG or is populated with a unit other than those accepted by USGS (i.e., meter, US survey feet, or international feet).
        • source_easting - Field is populated incorrectly, with inaccurate easting coordinates or incorrect values, or exceeds three decimal places in precision.
        • source_northing - Field is populated incorrectly, with inaccurate northing coordinates or incorrect values, or exceeds three decimal places in precision.
        • source_elevation - Elevation values are inaccurate, inconsistent with the “source_vertical_unit” field or exceed three decimal places in precision.
        • project_id - Project identification listed is inconsistent with USGS assigned Project identification number.

 

  • Incorrect Geometry - Any errors involving the geometric properties of the survey point file provided for review. Errors will be called more specifically as detailed below.
    • Quantity - Number of survey points provided fails to satisfy the minimum specified by USGS guidance on requirements based on area of the Project.
    • Spatial Distribution - Survey points are not “well-distributed,” as defined by and in accordance with applicable Lidar Base Specification and/or survey report. Any limitations in achieving well-distributed survey point collection should be noted in the survey or Lidar Mapping Report.
    • Location -  Survey point(s) located outside of Defined Project Area (DPA) or EPSG Area.
    • Z-Value - Any issues involving the vertical (Z) measurements of the survey points. These can include but are not limited to:
      • Geopackage not being Z-Enabled.
      • Z values of attribution not correctly matching actual Z values of the point geometry.

 

  • Spatial Reference - Any errors involving the spatial reference of survey points. Examples include, but are not limited to:
    • Coordinate Reference System used for some, or all, survey points is incorrectly formatted.
    • Coordinate Reference System does not match requirements for Project as defined in Task Order.
    • Vertical and/or horizontal information is incorrect or missing.