High Accuracy Helicopter Lidar & Mapping

Jeffrey B. Stroub, CP,RLS,PPS,SPVice President Business Development

September 9, 2014

Jeff Stroub CP, RLS, PPS, SPVice-President Business DevelopmentSeptember 16, 2014

Understanding USGS LiDAR Base Specification Version 1.0

USGS LiDAR Base Specification Version 1.0

Goal USGS Base Specification

• Consistency – all USGS funded LiDAR Collections• USGS Interest is only LiDAR Derived Elevation Models• USGS Scope specific to their mission

– Hydro-Flattened surface – Hydro Enforced optional surface

• A carefully planned project may support other uses– USGS Version 1.1 in concept stage

U.S. Department of the InteriorU.S. Geological Survey

H. Karl Heidemann, GISPPhysical ScientistU.S. Geological Survey/EROS

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Background• In response to ARRA funding for USGS LiDAR collection,

development of a common minimum specification was begun in early 2009; the USGS NGP Lidar Base Specification, Version 1.0 was published in the summer 2012: .

• Time marches on …– NEEA Study on national LiDAR value published– The 3DEP established – ASPRS Accuracy Standards developed– Technical advances in the industry

• The now 5 year-old v1.0 Specification requires revision

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ASPRS Accuracy Standard Alignment • Alignment to ASPRS Accuracy Assessment Methodology

– NVA on point cloud assessed in single-return areas– VVA must be met (excluding delineated Low Confidence areas)– CVA is no longer reported

• Use of ASPRS recommended check point quantities

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Lidar Specification Changes QL2 is the minimum QL for 3DEP lidar collections.

2 points/m2

10 cm RMSEZ

LAS Version 1.4 is required. OGC Well Known Text Georeference information required

LAS Point Record Format 6, 7, 8, 9, or 10 are required. Proper use of Withheld and Overlap flags required.

Metadata for LiDAR files. LiDAR metadata tags suggested in v1.0 are required in v1.1.

LiDAR Specification Changes 2GB limit on swath file size has been removed.

Flightline Overlap requirement has been removed.

Scan Angle guideline has been removed.

Classification: Two added required classifications Bridges (17) High Noise (18)

Classification Accuracy for : QL2, QL1, and QL0 Test areas are now 1 square km, not 1 km square

LiDAR Accuracy Accuracy is dependent on:• Flying height• Sensor parameters

– Rep Rate– Scan Angle – Scan frequency

• System accuracy • Terrain• Vegetation• Baseline distance

– Location of base station to Aircraft

• Plan based on– Workable blocks of data– Delivery tiles– Baseline requirements– Flightline distance

limitations– Control locations– Accuracy– Application– Topography

LiDAR Project Planning

Processing Steps1. GPS Processing2. QC GPS3. IMU Processing4. QC IMU5. Calibration6. Check Calibration7. LAS point Cloud Output8. Verify coverage9. Classification

1. Sub sample for Macros2. Breakline generation

10.QC Manual Editing11. QC process12.Generation products13.Check Deliverables

Full Return Surface Model

LiDAR Classified .LAS File

Classification

Manual Editing

USGS ProductHydrologically – Flattened (Hydro-Flattened) – USGS Standard Product

Processing of LiDAR derived surface (DEM or TIN) so mapped water surfaces are flat from bank to bank, and rivers demonstrate a gradient change. Breaklines are used to establish elevations for water surfaces consistent with surrounding topography, and produce aesthetically acceptable water surfaces in final DEM or TIN.

Hydro flattening is driven solely by USGS cartographic mapping needs.

Breaklines• Breakline specifications vary by project and point

densities• Hydrologically-Conditioned (Hydro-Conditioned)

– Processing of a DEM or TIN so that the flow of water is continuous across the entire terrain surface whether flow in channel or not (evaluation basin / large areas)

• Hydrologically –Enforced (Hydro-Enforced)– Process of mapping water bodies so that lakes and

reservoirs are at level surface and so that streams flow downhill……(typically used for hydrologic and hydraulic modeling) – optional product

Bare-Earth Surface without Breaklines

Bare-Earth Surface with Breaklines

Breaklines

• If a DEM is required for a project and the breaklines fail acceptance, the DEM will fail acceptance.

• LiDAR industry has come along way in breakline development

• Breakline generation depends on source material – formerly Photogrammetry now LiDAR derived

Breaklines

• USGS Spec.

• 100 Feet River• 2 Acre

Breaklines

Breaklines

Breaklines

BreaklinesA Cross Section is viewed to see if the red XBAR line is set at the lowest elevation.The red XBAR line elevation can be changed if not correct.

Breaklines

After placing the red XBAR lines and setting their elevation so they monotonic you are ready to drape water breaklines

BreaklinesThis is a 5000’ x 5000’ Tile

This is a full tile with the water bodies and river collected. The red XBARs have been placed and the elevations have been set.

BreaklinesThe Final check to make sure the river breaklines are monotonicis to run contours. A surface is created with the river breaklines only. Contours are developed for That surface and contours are created crossing only the river breaklines.

Bare-Earth Surface

Bare-Earth with Breaklines – Hydro Flattened Surface

Bare-Earth Surface - Hydro Flattened

Bare-Earth with Contours processed through a Hydro Flattened Surface

Hydro Flattened - Bare-Earth Surface

Hydro Flattened Surface with Flood Stage Introduced

Bare-Earth with Breaklines – Hydro Enforced Surface

Bare-Earth Surface Hydro Enforced

Bare-Earth with Contours processed through a Hydro Enforced Surface

Hydro Enforced Bare-Earth Surface

Hydro Enforced Surface with Flood Stage Introduced

Accuracy

Accuracy

Standard USGS Deliverables

• Hydro-flattening per USGS water surface requirements• No single line drain breaklines – optional• Metadata – extraneous• Raw point cloud in .LAS – file size fixed at 2gb• Classified Point cloud – USGS standard Bare-Earth

Surface (Raster DEM) per classification scheme• Breaklines per USGS specification - ESRI feature class• No contour processing

Project Reporting• Designed to USGS and other agency requirements

Questions and AnswersThank You