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Lesson 3: Create Derivative Products from Lidar with UniDEM

This tutorial illustrates methods to derive additional data from LAZ data files.

For more lessons visit Working with Lidar Point Clouds.

The sample data used in this lesson is 3DEP lidar data in two LAZ files containing LAS version 1.2 points located in Madison, MS, USA. Prior to commencing this lesson, please download the sample data:

This lesson will take approximately 20 minutes.

The following video executes the steps in the tutorial.

1. Load and upgrade to LAS 1.4

  1. Click uniDEM icon
  2. Select Load LIDAR
  3. Open both LAZ files
  4. Select Upgrade file format to LAS version 1.4
  5. Click Yes to all files into single dataset
  6. Enter Madison for the combined dataset name
  7. Data is displayed in the Table Of Contents (TOC)
upgrade to las v1.4

Help references:

Load LIDAR | Data Management | Table of Contents

2. Display Lidar Point Cloud

  1. Right Click Madison in the TOC
  2. Select Check All
  3. Lidar points are colored by CLASS
  4. Within the LIDAR tab
    • Set (Point) Density to Normal
    • Set Point Size to Large
show lidar dataset

Help references:

Table of Contents | Point Density | Point Size

3. Crop and Merge Lidar Point Clouds

  1. Create Second Data View
    • Press Ctrl-N to create a new data view
    • Press Ctrl-T to tile the two data view windows
  2. Click into left data view window
  3. Press P to start the polygon drawing tool
  4. Press Shift + Left Click to add vertices to draw a polygon in the middle of the lidar points
  5. Within the Lidar tab click Crop/Merge Points
  6. Click Select All to select both LAZ files
  7. Name the new lidar file crop
  8. Select Current drawing to crop data to the polygon
polygon to crop lidar points
  1. Click into right data view window
  2. Right click on the cropped dataset in the Table of Contents
  3. Select Check All to display the cropped dataset.
cropped lidar points

Help references:

New Window | Tile Windows | Polygon Drawing Tool | Crop/Merge Points | Table of Contents

4. Create a Digital Elevation Model (DEM) Raster from Lidar

A DEM represents a raster grid of the bare earth surface with all buildings and vegetation removed.

Create DEM Raster

  1. Within the LIDAR tab click Points to DEM
  2. Select A loaded point cloud from the input
  3. Select the Madison dataset
  4. Click Select All to pick both LAZ files
  5. Select Copy From an existing dataset to define projection and extents
  6. Select the Madison dataset to define the extents
  7. Click OK to use the recommended pixel spacing and extents
  8. Click OK to use Point Elevation
  9. Click OK to use the Average algorithm
  10. Select LAS class Ground (2)
  11. Click OK to "Use all points"
  12. Name the output as DEM - licensed mode only. Otherwise the layer will be named New DEM
  13. Click into right data view window
  14. Right Click New DEM in the Table of Contents
  15. Click Check All to display the DEM
Note: If using uniDEM Free mode right click on New DEM in TOC, select Rename and name dataset "DEM".
dem from lidar

Fill Missing Data

  1. Press Ctrl-A to select all pixels in the DEM
  2. Within the DEM tab click Triangulation
  3. Click OK to use "10" pixels for triangulation size
  4. Click OK to use "1" pixel for smoothing
  5. Click OK to add interpolated points inside void
  6. Press Esc key to clear the selection
void filled dem from lidar

Help references:

Points To DEM | Triangulation | Custom Shader Min | Custom Shader Max | Table of Contents

5. Create a Digital Surface Model (DSM) Raster from Lidar

A DSM respresents raster grid of the maximum measured height above bare ground including buildings and vegetation.

Create DSM Raster

  1. Within the LIDAR tab click Points to DEM
  2. Select A loaded point cloud from the input
  3. Select the Madison dataset
  4. Click Select All to pick both LAZ files
  5. Select Copy From an existing dataset to define projection and extents
  6. Select the Madison dataset to define the extents
  7. Click OK to use the recommended pixel spacing and extents
  8. Click OK to use Point Elevation
  9. Select the Maximum algorithm and Click OK
  10. Click Select All to use all classes when creating the grid
  11. Click OK to "Use all points"
  12. Name the output as "DSM" - licensed mode only. Otherwise the layer will be named New DEM(1)
  13. Click into left window
  14. Right Click DSM in the Table of Contents
  15. Click Check All to display the DEM
  16. Right Click Madison lidar dataset in the TOC
  17. Select Uncheck All to turn off the lidar points
  18. Within the Home tab set the Shader Scope to Custom
    • Set Min. to 100
    • Set Max. to 125
Note: If using uniDEM Free mode right click on New DEM in TOC, select Rename and name dataset "DSM".
dsm from lidar

Fill Missing data

  1. In the TOC double Click DEM in the DSM dataset to make the DSM active for editing
  2. Press Ctrl-A to select all pixels in the DSM
  3. Within the DEM tab click Triangulation
  4. Click OK to use "10" pixels for triangulation size
  5. Click OK to use "1" pixel for smoothing
  6. Click OK to add interpolated points inside void
  7. Press Esc key to clear the selection
void filled dsm from lidar

Help references:

Points To DEM | Triangulation | Table of Contents

6. Create a Height Above Ground Level (AGL) raster

An AGL is a raster grid of the highest height of a point of a first surface above ground height illustrating building and vegetation heights. This is created by subtracting the DEM from the DSM.

  1. Within the DEM tab click Difference
  2. Select the DSM dataset for raster 1 in the dropdown list
  3. Select the DEM dataset for raster 2 in the dropdown list
  4. Click OK to select DEM for the output type
  5. Enter AGL to name the difference output
  6. Press Esc key to clear selection
  7. Close right data view
  8. Click into the remaining data view
  9. Press Ctrl-T to scale the data view
  10. Right click DSM,or New DEM(1) in the TOC and select Uncheck All to turn off DSM
  11. Right click AGL in the TOC and select Check All to turn on AGL
  12. Press F12 key and enter "20" to set the elevation color scale to ±20m
height above ground from lidar

Help references:

Difference (DEM) | Tile Windows | ±N | Table of Contents

7. Create an Intensity Image from Lidar Metadata

Each LAS point has metadata holding the intensity return of the light pulse from the source. Intensity returns are variable dependent on the material that the pulse interfaces with and can be used for interpretation and classification.

  1. Within the LIDAR tab click Points to Image
  2. Select A loaded point cloud from the input
  3. Select the Madison dataset
  4. Click Select All to pick both LAZ files
  5. Select Copy From an existing dataset to define projection and extents
  6. Select the Madison dataset to define the extents
  7. Click OK to use the recommended pixel spacing and extents
  8. Select intensity to use for the image value
  9. Select 16-bit values for output format to create a gray scale image
  10. Select Maximum for the algorithm to use
  11. Click Select All to use all classes when creating the grid
  12. Click OK to "Use all points"
  13. Name the output as Intensity - licensed mode only. Otherwise the layer will be named New Image
  14. Right Click Intensity (New Image) in the TOC
  15. Click Check All to display the Intensity image draped over the AGL
  16. Scale Image for viewing
    • Right Click Intensity dataset and select Properties
    • Select Auto Contrast (Global) radio button and click OK
las intensity image

Help references:

Points To Image | Table of Contents