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.

Goals

Task 2

• Geodatabase of bridges

Module downloads

• Decompress and save to your root GIS folder
• tools > notebook, toolbox, and laszip64.exe
• data > lidar tile grid layer

Lidar

• 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

• Kentucky Aerial Photography & Elevation Data (KYAPED) program
• Collected during leaf-off conditions
  • no snow and water levels at or below normal.
• Point cloud has max 2.23-foot point horizontal spacing.

Goals

• 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.

Classification

• 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?

Point cloud Derivatives

DEM

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

DSM

• 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.

Decompress

• 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.

Goals

• 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.

Module downloads

• Decompress and save to your root GIS folder
• tools > notebook, toolbox, and laszip64.exe
• data > lidar tile grid layer

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.

LAZ to LAS

• 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.

Analysis

• 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.

QA/QC

• 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?

Layout

• 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.

Submission

• Export layout as JPG and upload to Canvas assignment page.

STOP

Addendum

• 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.