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Lidar Mapping Report

USGS requires descriptive metadata to accompany 3DEP datasets. This documentation is intended to convey characteristics of the lidar mapping campaign as well as the data. This lidar mapping report guidance identifies key components of the data collection and processing that may be useful to USGS staff reviewing the data as well as data users.

Status of this revision: Published in Lidar Base Specification 2021 rev. A

Current requirement: See the current Lidar Base Specification--Deliverables section for relevant current requirements. 

Approved revision:

The Lidar Mapping Report (LMR) shall include a graphic showing flightline vectors by lift, delivery block tiles, and DPA. It will convey, at a glance, the different collection flights covering the delivery block tiles. 

The LMR shall also include the following sections:

  • Data Acquisition and Processing including 

    • A brief write-up of the project to include the USGS 3DEP Lidar QL and any additional products and services required as part of the task order.

    • A brief write-up to include any circumstances encountered during acquisition or processing that resulted in data anomalies, such as

      • adverse environmental conditions (for example, heavy smoke, standing snow, flooded land, full leaf-on conditions);

      • information regarding tidal constraints including tide-gauges used, tidal datum, and tidal windows;

      • issues with data collection (for example, lidar sensor problem, ABGNSS interference); 

      • reference to any ancillary files, such as low confidence polygons that are used to delineate data anomalies. 

  • ABGNSS-inertial Processing including:

    • A write-up of the process including processing software used.

    • Comprehensive processing reports with graphics from POSPac, Inertial Explorer, or similar software (these can be provided as appendices and are satisfactory replacements for any of the following items if requested content is contained in those reports).

    • List or graphics of any reference stations used for differential correction.

    • Confirmation of processing reference frame.

    • Graphics of processing interface to show trajectory data and labeled reference stations for each lift. If precise point position used, a graphic of trajectory only. 

    • Graphics of processed plots for each mission/flight/lift to include, at a minimum:

      • forward/reverse separation of trajectory,

      • estimated accuracy of trajectory,

      • and any additional plots that contractor used in the analyses of trajectory quality and believed to be of value. 

  • Point cloud creation including:

    • Summary of original point cloud (LAS) creation software and processes used, to include:

      • version—this can be represented with a screenshot embedded in the document;

      • coordinate reference system (reference frame, projection, units, vertical datum, geoid height model) selected for point output—this can be represented with a screenshot embedded in the document; 

      • and any supporting graphics the contractor believes are of value.

  • Geometric quality including:

    • Write-up of point density/spacing assessment and results for the dataset including which points were tested and the methodology for assessing density/spacing. 

    • Write-up of geometric adjustment to include

      • a summary of sensor model calibration, boresight process, and subsequent swath adjustment process, and

      • a summary of smooth surface precision and interswath accuracy analyses.

    • Graphics and statistics to support smooth surface precision analyses.

    • Graphics and statistics to support interswath accuracy assessment to include:

      • Swath separation image graphics and write-up of processes and settings used to create these images. Settings to be documented include image GSD, color ramp values, points used, surface algorithm (TIN, point-in-cell, other). This can be documented with a screenshot embedded in the document. 

      • Reporting of other methodologies for assessing interswath and any supporting statistics. 

    • Any additional graphics and statistics the contractor believes may be of value in conveying relative accuracy of the point cloud data.

  • Production including:

    • Point-cloud flagging and classification routines to include:

      • software used,

      • process for assigning withheld bit flags,

      • process for assigning additional classification codes (for example, vegetation by height, segmentation, building classification).

    • Breakline placement methodology and elevation conflation method including:

      • Description of hydrologic features treated with breaklines (for example, area of water body, stream width).

      • Breakline compilation methodology including:

        • software used and whether compilation was manual, semi-automated, or fully automated,

        • elevation conflation method,

        • QA/QC procedures employed to confirm breaklines meet 3DEP requirements,

        • list of any ancillary imagery or data used for breakline compilation including imagery sources and acquisition dates. 

      • Raster production including interpolation method used for bare earth DEM creation and the version of GDAL used to define the raster CRS.