LiDAR & Ground Truthing
Situated in Tacoma’s historic Warehouse District, the University of Washington Tacoma (UWT) continues to evolve and expand since its opening in 1997. Currently serving nearly 5,000 students, the university has recently completed renovations on and/or newly constructed a new science building, student housing and on campus YMCA, with plans to expand further.
An accurate and updated GIS layer which includes these new building footprints is a critical component for planning and development purposes.
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For more please visit www.tacoma.uw.edu
or
An Expanded University of Washington Tacoma Campus
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Click the image for a printable version of this analysis
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LiDAR Data
LiDAR is an acronym that stands for ‘Light Detection And Ranging’. It is a remote sensing procedure that uses laser pulses to determine the distance between a LiDAR unit and another object or surface. The Data used in this analysis was LiDAR point cloud that was collected during aerial overflights of Pierce County.
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Bare earth LiDAR data includes only single returns (Figure 1) yielding ground elevations. Beam pulses that encounter reflective surfaces including buildings or trees create data sets that include all structures and varying heights (Figure 2).
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Ground elevations were interpolated using the Inverse Distance Weighting (IDW), which has been shown to be appropriate for LiDAR data and results in the creation of a floating-point raster.
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Original UWT Campus building footprints were joined to the LiDAR data rasters in order to create building ground and height attributes.
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Figure 1: Result of bare earth LiDAR surface interpolation
Figure 2: Result of all returns LiDAR surface interpolation
Ground Elevations & Building Heights
Building heights and building footprint elevations were interpolated fron LiDAR data using two methods:
Method 1. Zonal Statistics: Uses mean values to infer heights and elevations
Method 2. Extract Values to Points: Creates composite height and elevation values using Bilinear Interpolation
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LiDAR data is relatively accurate, but not necessarily precise, thus these two different methods will resulted in different values due to differences aggregation methods. The composite, Extract Values to Points results were used as building heights, as these values using multiple points to determine elevations and heights. Additional confirmation of the accuracy of these values was provided by groundtruthing and known relative building heights.
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Table 1: Building height interpolation results and differences
Table 1: Building height interpolation results and differences
Table 1: Building height interpolation results and differences
Building Extrusion in ArcScene
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In ArcScene, building polygons and an orthophoto were draped over the bare earth grid values used as a 3D topographical map (Figure 3)
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Building footprints were extruded based on each feature's minimum interpolated building height to create 3D symbology from 2D features (Figure 4)
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Ground truthing revealed errors in building footprints, building heights as well as missing buildings
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Figure 3: Draped building footprint polygons, orthophoto and bare earth grid.
Figure 4: Extruded buildings over orthophoto visualized using ArcScene.
Creating an Updated Campus Map
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A high resolution Ortho Image Mosaic was created and used to digitize missing buildings and correct building footprints
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One building which will be breaking ground (AIB) in the next UWT Master Plan Phase was also digitized
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Differences in building heights were determined via ground truthing and building attributes updated
AIB Academic Innovation Building
BB Birmingham Block
BHS Birmingham Hay & Seed
CAR Carlton Center
CP Cherry Parkes
C17 Court 17
DOU Dougan
GWP Garretson Woodruff & Pratt
JOY Russell T. Joy
KEY Keystone
LBH Laborers Hall
MAT Mattress Factory
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MDS McDonald Smith
WPH William W. Philip Hall
PNK Pinkerton
PKT Pinkerton Turnaround
SCI Science
SNO Snoqualmie Building
TLB Tioga Library Building
UWY University Y Student Center
WG Walsh Gardner
WCG West Coast Grocery
WHT The Whitney
Figure 5: Revised 3D rendering of UWT Campus.
Resources/References
Cartographer/GIS Analyst: Tracie S. Barry Contact: barryts@uw.edu
Created: May 5, 2019
Software: ArcMap & ArcScene 10.6.1
Projected Coordinate System:NAD 1983 HARN StatePlane Washington South FIPS 4602 Feet
Data Sources: UWT GIS Certificate Program, S Schunzel 2015 Orthophotos, UWT Master Plan Update 2008