Module 02


Yesterday in the Great Smokies
Webcam archive
GEO 509: Workshop in Geospatial Technologies

Maps of bridges!

in no particular order

Jobs in GIS

  • Trends in GIS competencies link
    • LiDAR data processing and analysis
    • Geospatial imagery data processing and analysis

KAMP Conference

  • Ky Assoc of Mapping Professionals annual conference next week in Lex.
  • Let's take a look at the schedule.

02: Infrastructure


Use lidar point clouds and their derivatives to describe the dimensions of flood-prone infrastructure and visualize the results. Primarily, we will try to find the bridge deck height above stream crossings and attribute the bridge point data made in the previous lab.

Task 2

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  • Light detection and ranging.
  • Active sensor
  • with multiple returns and attributes.
  • Creates a point cloud (massively sampled locations).

Point cloud attributes

  • x, y, z position
  • time
  • intensity of return
  • Algorithms classify point, e.g., ground, vegetation, building, etc., and assign a class value.

Airborne lidar

  • Massive sampling of earth's surface by plane.
  • Uses GPS and IMU (inertia measurement unit) to map point.
  • While can penetrate canopy, cannot 'see' under solid structures.
  • I.e., cannot see under our arches, bridges, overhangs.

Terrestrial lidar

  • Ground-based sampling.
  • Can build true 3D model, e.g., see under and inside.
  • Increasingly available in consumer products.

Kentucky project


  • Create elevation products for bare-earth conditions.
  • A statewide 5-ft resolution DEM is now available.
  • Collection 2010–present.
  • Two phases with different resolutions.
  • Completely free.


  • Algorithms classify point
  • as ground, noise, or unassigned.
  • Unassigned points are above-ground features.

Lidar challenge

  • Massive file size
  • State divided into 46,105 tiles
  • with one tile ~ 500 MB.
  • Difficult to visualize (today).
  • How to handle these file sizes?
9 GB point cloud ➡️ 250 MB raster

Point cloud Derivatives

Airborne point clouds can be reduced to high-resolution raster imagery.


  • Digital Elevation Model
  • Most often bare-earth surface
  • Point cloud class code 2


  • Digital Surface Model
  • Includes the reflected surface
    • buildings, trees, bridges, etc.
  • Point cloud class codes 1, 2, 9, 17

Data file formats

  • LAS file
    • Laser format most common in GIS
  • LAZ file
    • A compressed LAS file
    • Most common storage format
    • Need a separate utility to decompress and use in ArcGIS Pro.
      • laszip.exe include in our tools folder


Create new ArcGIS Pro project

  • Create a folder in your project called
    • las
  • Load the Kentucky_5k_PointCloudGrid layer from the downloaded GDB.
  • Download two adjacent tiles
    • Make sure they are the same Phase, i.e., same version.


  • Drag and drop the LAZ file, one by one, onto the laszip.exe application
  • Verify that you have two LAS files.

Create LAS dataset

  • Treat multiple tiles as a single layer.
  • Visualize in a new Scene.

LAB 02


  • Attribute our bridges with height above stream.
  • Visualize three bridges with point cloud representations and verify the height with a direct measurement in an ArcGIS Pro Local Scene.

What we know so far

  • We have corrected point locations for our bridges.
  • We can sample the value of the DEM at that point to get stream surface elevation.
  • Note: Bridges are removed from the DEM so we can model hydrology.

What lidar gives us

  • Our lidar point cloud shows above ground features.
  • We can sample the value of the DSM at that point to get bridge surface elevation.

Minus function

  • For each bridge point, subtract the stream surface elevation (DEM) from the bridge surface (DSM) elevation.
  • That will give us the height above stream.
  • Add that value to the bridge point attribute table as a new field that we'll call "Z".

Sources of errors

  • Point locations are not exact.
  • Canopy cover over bridge.
  • Parallax: Displacement of high bridge surfaces in the aerial view.

Methods overview

  • Extract three bridges to a new ArcGIS Pro project.
  • Download LAZ files for the three bridges AOI.
  • Create point clouds and analysis for each AOI.
  • Visualize in layout.

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Jupyter Notebook

  • Open lab-02-process-heights.ipynb in ArcGIS Pro.
  • Modify cell to point to your root GIS folder, new project, new layer, etc.

Next three cells

  • Create our local environment and load external data.
  • Buffer our bridges and extract the lidar tiles that we'll download.

Download LAZ tiles

  • You should have the grid layers that reference the tile downloads needed in all of your bridge AOIs.
  • Interactively download the LAZ files.


  • Next cell will convert all LAZ files in the download folder to LAS files
  • and create a LAS dataset.
  • You will not see points until you zoom in closely.


  • The last cell extracts point clouds and creates a few raster datasets
  • for each bridge AOI.
  • The OBJECTID attribute relates each bridge point to the analysis output.

Visualize each AOI

  • Create New Local Scene and add three layers:
    • DEM to Ground Surface
    • aerial imagery to 2D Layer
    • LASD to 3D Layer.


  • Open your bridge's point layer attribute table.
  • Measure the bridge height above stream and compare to Z attribute.
  • Do we need to move our points?


  • with five maps or scenes:
    • State locator map.
    • Regional locator map.
    • Three scenes, one for each bridge, showing the calculated and measured height of the bridge above the stream.
  • The style of the layout is completely up to you.




  • Model builder tools in toolbox to create LASD and analysis for our locations.
  • They will not decompress the LAZ files, but you can use the notebook to do that.