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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…
5
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
7
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
38
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/
43
https://imap.maryland.gov/Pages/training-documents.aspx• Access Maryland LiDAR Topography Server
• ArcGIS for Desktop LiDAR Tutorials
44
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
45
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
46