Presentation Outline• What is LiDAR• Use Cases• Technology | Components• How is it acquired• Point Cloud• Quality Levels [Point densities | Accuracy]• Data Formats and Compression [LAS > LAZ]• Point Cloud to Surface Models [DEM | DSM]• Hydro-Flattening | Enforcing | Conditioning• Accessing Maryland LiDAR• ArcGIS Desktop DEMO

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What is LiDAR?Light Detection and Ranging

Remote sensing method used for measuring variable distances from an object back to the sensor.

Light in the form of a pulsed laser.

Ranges (distances), combined with position and orientation data.

Results in a dense cloud of points – “point cloud”

3Source: NOAA

Light Detection and Ranging

Each point in this cloud contains 3-dimensional spatial coordinates (X, Y, Z)

Generate surface models Digital Elevation Models (DEMs) Digital Surface Models (DSMs)

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Using LiDAR for…

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Hazard assessment Risk management Ortho rectification Forestry Agriculture Emergency management Damage assessment Viewshed analysis

Natural resource management Archaeology Climate monitoring City planning Meteorology Mining operations Hydrologic modeling Geologic surveys

Source: GISGeography.com, 2018

LiDAR Acquisition

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LiDAR Components

• Laser Scanner and Sensor• Upwards of 400,000 pulses per second• Sensor receives reflected echo from emitted pulse as waveform

• GPS – Global Positioning System• Tracks location of the plane as it collects data

• IMU – Inertial Measurement Unit• Tracks pitch, roll and yaw of the plane as it collects data

• Ground Station• Provides a ‘correction’ factor for the GPS in the plane

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Source: Dashora, Lohani, & Deb, 2013

LiDAR Acquisition

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LiDAR Returns

Discrete Returns

Waveform Returns

9Source: GISGeography.com, 2018

LiDAR Returns

10Source: GISGeography.com, 2018

Point Classifications

11Source: ESRI

Point Classifications

12Source: GISGeography.com, 2018

2018 Ellicott City QL1 LiDAR Point Return – Cross Section Profile

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2018 Ellicott City QL1 LiDAR Point Classification – Cross Section Profile

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Aggregate Nominal Point Spacing and Density for LiDAR Quality Levels

16Source: USGS

Relative Vertical Accuracy for LiDAR Quality Levels

17Source: USGS

Absolute Vertical Accuracy for LiDAR Quality Levels

18Source: USGS

Minimum Digital Elevation Model (DEM) Cell Resolution

19Source: USGS

Point Cloud Format

LAS – Required point deliverable format from data producers (American Society for Photogrammetry and Remote Sensing | USGS)

LAZ – Open source compression format for LAS. Upwards of 90% compression.

Visit https://laszip.org/ to check out LASzip, the free open source LAS compression/LAZ extraction tool; part of the rapidlasso GmbH product suite https://rapidlasso.com/lastools/

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Point Cloud to TIN

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Surface Model Interpolation

Interpolation Types:•Binning •Triangulation

Interpolation Methods:•Linear interpolation•Natural Neighbor interpolation

22Source: USGS

Digital Surface Model (DSM)

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Filter LAS file to return ALLclassified points, except Noise and High Noise

1st Return only.

Digital Surface Model (DSM)

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Example of Noise / High Noise

Eastern Shore –Caroline County 2013

European Starlings… Most likely the culprit here

Digital Surface Model (DSM)

25Source: Ellicott City LiDAR, 2018

Digital Elevation Model (DEM)

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Filter LAS file to return only Groundclassified points.

ALL Returns

Digital Elevation Model (DEM)

27Source: Ellicott City LiDAR, 2018

Hydro-flattened

• Breaklines are used to force the water surfaces to be flat/constant elevation.

• Not driven by any hydrologic and hydraulic (H&H) modeling requirements

28Source: USGS

Hydro-enforced

• Includes hydro-flattening

• Enables hydrologic and hydraulic models to allow the flow of water through culverts and under bridges

29Source: USGS

Hydro-conditioned

• Similar to hydro-enforcement

• Erroneous sinks and pits in the dataset are filled to aid in water flow across the entire surface model.

30Source: USGS

LiDAR Intensity

• Strength of the returned laser pulse

• Partly determined by an objects reflectivity

• Aid in feature detection

• Supplemental dataset for aerial imagery

31Source: ESRI

LiDAR Intensity

32Source: Ellicott City LiDAR, 2018

ESRGC | DOIT Partnership

• Supporting LiDAR initiative in Maryland since 2013

• County and Statewide surface models and derivatives

• Aspect

• Slope

• Hillshade and Multi-directional Hillshade

• Shaded Relief

• DEM (feet and meters)

• Download options/tools | Topography viewer/server

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So What’s Available in Maryland?• 2011

• Anne Arundel | Calvert | Howard | Somerset | Wicomico | Worcester• 2012

• Frederick | Somerset | Washington | Wicomico• 2013

• Cecil | Dorchester | Harford | Montgomery | Queen Anne’s• 2014

• Charles | Prince Georges | St. Mary’s | Washington D.C.• 2015

• Baltimore City | Baltimore | Carroll | Garrett | Kent | Talbot | • 2017

• Calvert | Anne Arundel• 2018

• Ellicott City | Prince George’s | Montgomery | Washington D.C.34QL1 in Red

Coming Soon

• 2018• Howard County (in QC)

• 2019• Wicomico | Worcester | Somerset (planned 2019/2020)

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Metadatahttps://imap.maryland.gov/Pages/lidar-metadata.aspx

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• The DATA about the data…

• When was the LiDAR collected?

• What is the resolution?

• NPS?

• Quality level?

• Spatial reference?

• Vertical accuracy?

• Hydrologic processing?

Options for Exploring Elevation Data in Maryland

•Dropbox Downloads

• Predefined DEMs• https://imap.maryland.gov/Pages/lidar-dem-download-files.aspx

• Predefined Point Cloud• https://imap.maryland.gov/Pages/lidar-download-files.aspx

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Options for Exploring Elevation Data in Maryland

• Maryland Statewide LiDAR Download Tool• https://lidar.geodata.md.gov:8443/ExpressZip

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ArcGIS REST Services Directory

• https://lidar.geodata.md.gov/imap/rest/services

Slope

Shaded Relief

Hillshade

DEM

Connect via ArcGIS Pro

• Search ‘Maryland LiDAR’ in Portal (All)

Slope

Shaded Relief

Hillshade

DEM

Owner: mdimapdatacatalog

Connect via QGIS

• WMS capabilities

Slope

Shaded Relief

Hillshade

DEM

Connect via ArcGIS for Desktop

• ArcGIS Server Connection

Slope

Shaded Relief DEM

Options for Exploring Elevation Data in Maryland

• MD iMAP Topography Viewer• https://geodata.md.gov/topoviewer/

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https://imap.maryland.gov/Pages/training-documents.aspx• Access Maryland LiDAR Topography Server

• ArcGIS for Desktop LiDAR Tutorials

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Online Training

• Extract from Image services

• Access Image Service Raster Functions

• Reclassify Raster Datasets

• Generate Contours

• Perform a ViewshedAnalysis

• Delineate a Watershed

• Build LAS Datasets

MSGIC: Elevation Working Group

http://msgic.org/elevation/

• Stay educated and informed on Maryland Elevation Data

• Hear about the latest acquisitions and what’s in the pipeline

• Discover training opportunities

• Network and collaborate with professionals in your industry

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Sources• NOAA

• ESRI

• Dashora, A., Lohani, B., & Deb, K. (2013). Two-step procedure of optimisation for flight planning problem for airborne LiDAR data acquisition. IJMNO, 4, 323-350.

• https://gisgeography.com/lidar-light-detection-and-ranging/

• https://my.usgs.gov/confluence/download/attachments/592446371/FAQ13.pdf?version=2&modificationDate=1524671104812&api=v2

• https://pubs.usgs.gov/tm/11b4/pdf/tm11-B4.pdf

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