USGS 3D Elevation

Program

Quality Control at the National

Geospatial Technical Operations Center

(NGTOC)

FL-ASPRS/UF Fall 2017 LiDAR Workshop

Lou Driber

Physical Scientist, Geospatial Liaison

U.S. Geological Survey

National Geospatial Program

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3DEP Products

• Classified Point Cloud

• Lidar-derived 1-meter raster bare-earth DEM

Products publish through the National Map

nationalmap.gov

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NGTOC Quality Control Overview

Standard Checks:

• Metadata

• Data processed to meet applicable

USGS Lidar Base Specification

• Lidar Point Cloud file (Swath LAS and

Classified LAS) header information/format

• Point Classification

• Spatial Accuracy

• Lidar-derived DEM meets required

format/specifications, accuracy, and

portrayal of bare-earth surface

DEM with Vegetation not removed

Profile of DEM with

Vegetation not removed

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Lidar Base Specification

▪ All current 3DEP projects adhere

to the USGS Lidar Base

Specification Version 1.2 adopted

November of 2014

▪ Many projects have customer-

specific requirements beyond the

LBS documented in the Project

Task Order or contract agreement

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Note: Doesn’t address Lidar Emerging Technologies

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3DEP Data Source Points

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Tools of the Trade

Workhorse

Provides a combination of advanced tools for

viewing header information, visualizing and classifying point

cloud data, conflating breaklines and exporting DEMs.

- ArcGIS with WMX Extension controls the USGS lidar QC workflow

- LP360 incorporates a set of toolbars that can be

run inside ArcMap as an extension.

- Combining the editing tools available fromArcGIS

and the toolsets available through LP360 provides a robust

set of functions supporting data validation and editing.

Generally used as a Qualitative tool to view and evaluate

3DEPDEMs

Offers a variety of open source tools to

quickly view and edit LAS header information

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Metadata

Inspected with FGDC Metadata Parser

2015 Suwannee River Water Management District Lidar Project

9999Data Content / Formatting

In-House Applications

▪ LAS_Check (in-house)

▪ Verify LAS 1.4 files follow format standards

▪ LAS_QC (in-house)

▪ Reads LAS header and point information

▪ Reports:

▪ Spatial Reference System

▪ Point Form ID

▪ Number of Classes Used

▪ Returns Used

▪ Point Density

▪ Intensity and Scan Angle

▪ GDAL (in-house)

▪ Checks each LAS file references correct coordinate system

▪ File expressed in the proper Well Known Text (WKT-LAS 1.4) format

▪ Las Point Classifications meets project requirements

▪ Point count totals are correct

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Procedures Include:

▪ Visually review the Swath and Classified LAS Point cloud for

missing data

▪ Horizontal Position check (relative) for issues such as sensor

miscalibration

Overlap area between two

flight lines showing relative

horizontal offset.

Swath Point cloud with Calibration Issues

Initial Qualitative Review

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Vertical Accuracy Review

Assumption:

▪ Check points are error free

▪ Any accuracy discrepancies are attributable

to Lidar Dataset

20 Checkpoints minimum (30 preferred)

for each major land cover class:

▪ ASPRS Guidance:

▪ Independent, well distributed

▪ NSSDAGuidance

▪ May be distributed more densely

in vicinity of important features

Other independent control used when

available (USGS, NGS, USACE)

3DEP QL2 (minimum)

RMSEz NVA≤ 10cm

Nominal Point Density ≥ 2.0

Nominal Point Spacing ≤ 0.71

SRWMD Check Point Distribution

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Vertical Accuracy Review

Tools

ArcMap

• Load Project Area Polygon and Check Points

• Verify

• Checkpoint Distribution

• Checkpoint Quantity

• Checkpoint Quality

LP360

• Load Swath files to compute NVA

• Compare value of checkpoint to those of the TIN at that location

• Verify

• Accuracy results computed to those reported by Contractor

13131313DEM Review

Swamp/Marsh misclassified as Class 2

bare-earth in Point Cloud

Visual Check: GlobalMapper

• NGTOC performs 100% manual review

• Inspected at 1:6,000 scale

DEM Min/Max Check GlobalMapper▪ Scans the selected elevation grid layers to find

and report the minimum and maximum values

▪ Drives to Pits or Spikes

14141414Lidar Point Classification

DEM: Vegetation Classified as Ground

ORANGE

GREY

Ground Points

Unclassified Points

Profile highlights

misclassified points

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DEM Review: Hydrography

• Verify DEM tiles are Hydro-Flattened

• Culverts are maintained (Not Hydro-Enforced)

• Bridges/Overpasses are properly removed

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DEM Review:

Floating Water Bodies

Hydro-Flattening Water Bodies

Typically caused by:

incorrectly conflating water breaklines

developing breaklines with incorrect elevation value.

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DEM Review

Hydro-Flattening Streams

Streams 100’ or greater are flattened in a downstream manner

“There is a minor step in surface water elevation located in the North Feeder Canal where there is no discerniblephysical reason for it...”

Remedy:Develop Accurate Breaklines

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DEM Review: Data Voids• Commonly results from void in Point Cloud

• Typical Causes

• Few returns over water Bodies

• Few returns over densely vegetated areas

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DEM Review:

Building Removal

• Cause for rejection

of both the DEM

and the point cloud

data

• Typically caused by

incorrect point

classification

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Meeting the Needs of Emerging

Lidar Technologies

Conventional Lidar or Linear Mode Lidar

Geiger-mode Lidar

Sigma Space Single-Photon

Lidar

Evaluating smoothness

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Thank-you

Lou Driber

Physical Scientist, Geospatial Liaison

U.S. Geological Survey

National Geospatial Program

ldriber@usgs.gov