lidar deliverables for gis users
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LiDAR Deliverables for GIS Users
Isaiah DitmerLiDAR AnalystAKSMC February 2013
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AeroMetric Company Overview
Geospatial Services Provider Historical Imagery
LiDAR
Photogrammetry
Satellite Imagery
Enterprise GIS
Notable Markets Include Large Scale Mapping
Airport Obstruction Surveys
Forestry & Environmental Studies
Transportation & Utility Mapping
Emergency Management
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dy·nam·ic (adj.) \dī- na-mik\ ˈ
marked by usually continuous and productive activity or change
The State of Alaska is dynamic
The Alaskan GIS Community is dynamic
LiDAR as a Geospatial tool is dynamic
Sounds like we’re in good company!
AKSMC 2013
Today’s Underlying Theme…
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LiDAR Products & UsesAn Overview
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Digital Elevation Models & Contours
Most Common LiDAR Deliverables
Generated from “Bare-Earth” classified LiDAR data and digitized breaklines
Innumerable uses, from infrastructure to hydrological analysis
Often used to generate other terrain-based GIS data sets such as aspect and slope rasters
AKSMC 2013
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River Valley DEM & ContoursHydro-flattened LiDAR data along Willow Fishook Road West of Hatcher’s Pass
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Mountainous DEMModels such as this are frequently used throughout Alaska for applications such as line-of-sight analysis and route planning
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AKSMC 2013
DTM Resolution Comparisons
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Digital Surface Models
Generated from First-Return LiDAR data in order to represent continuous surface as viewed from above
Used to analyze relationship between terrain and natural or man-made obstructions above it
Especially convenient for raster analysis
AKSMC 2013
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Seward, Alaska DSMModel includes tree canopy as well as man made structures.
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Seward, Alaska DEMBare-Earth model of terrain that could be used to analyze feature heights etc. from DSM
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LAS Point Cloud Data
LAS Data is inherently attribute rich Each file consists of a Header, Variable Length
Records (VLRs), and Point Records
While ground / non-ground is the base classification, endless options abound
New LiDAR tools in ArcGIS 10.1 increase accessibility for end users to this richness
AKSMC 2013
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Fully Classified LAS DataUnique point classes used for structures, transmission lines, and vegetation, in addition to the bare-earth terrain
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LiDAR Standards & SpecsA Brief Overview
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Data Resolution
LiDAR data resolution referred to as either “Nominal Point Spacing” (NPS) or Point Density (in terms of points per square meter)
Related as follows:
USGS Base Specification Calls for an NPS of 2 meters or less (or a density of at least 0.25 ppm^2)
High accuracy airborne LiDAR typically requires densities of 6 – 10 ppm^2
AKSMC 2013
density
1NPS
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Vertical Accuracy
Determined through comparisons with surveyed ground data
The Fundamental Vertical Accuracy (FVA) of a LiDAR data set is reported as RMSEz * 1.960, which gives the NSSDA 95% confidence interval
Supplemental Vertical Accuracy (SVA) checks in categories other than “open terrain” may be desired and /or required
AKSMC 2013
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Hydro-Flattening
USGS Base Specification requires lakes at single elevations, rivers flat bank-to-bank and following gradient of surrounding terrain.
Breaklines to be digitized for lakes of 2 acres or greater surface area, rivers of 100 feet or greater nominal width
Goal is for DEMs to represent water bodies in a “cartographically and aesthetically pleasing manner.”
AKSMC 2013
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Hydro-Flattened Water BodiesHere the flattened wireframe is shown illustrating how software flattens lakes using breaklines
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AKSMC 2013
Hydro Enforcement Comparison
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LiDAR ProcurementAll Things Considered
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A Good Starting Point…
Before ironing out the details of a Scope of Work, consider the following questions, and discuss them with a LiDAR consultant if possible:
What will this data be used for ultimately?
Who will ultimately be using this data?
Will this data need to tie into existing data sets?
What products will be derived from this data set?
AKSMC 2013
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Product Considerations
What resolution of data do you need? Are additional/ unique classifications desired?
Is hydro-flattening or hydro-enforcement required? USGS or custom tailored specifications?
Is vertical accuracy a concern? Is vertical accuracy in additional land cover categories a concern?
Further questions? Get in touch!
AKSMC 2013
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Relevant Sources:USGS LiDAR Base Specification v 1.0http://pubs.usgs.gov/tm/11b4/
ASPRS Guidelines Vertical Accuracy
Reporting www.asprs.org/a/society/committees/lidar/Downloads/Vertical_ Accuracy_Reporting_for_Lidar_Data.pdf
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