Lidar Analysis of Vegetation Structure

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This exercise was initially created as a session in a GIS training for the U. S. Fish and Wildlife Service in May, 2016 by Doug Newcomb.

Session Objectives

At the conclusion of this session, you will be able to:

  • Open GRASS GIS and Create a Location from an existing file
  • Link external raster elevation data to the Location
  • Import LAS point cloud data to assess DEM accuracy
  • Import LAS point cloud data to create various vegetation structure products
  • Export raster vegetation structure data layers from GRASS to GeoTiff

Material Created By: Doug Newcomb (May 2016)

Software: GRASS 7.2

Directory Path: D:\grasslidar (assumed at some places, use any directory you want)

Image Files: D05_37_20026801_20141209.tif D05_37_20026803_20141209.tif D05_37_20026802_20141209.tif D05_37_20026804_20141209.tif

LAZ format LiDAR files: LA_37_20026801_20141209.laz LA_37_20026803_20141209.laz LA_37_20026802_20141209.laz LA_37_20026804_20141209.laz

Data can be accessed online here

Elevation data is commonly used in landscape analysis, but it is also quite useful in vegetation analysis. This exercise will walk you through basic analysis of a LiDAR point cloud to better understand vegetation structure.

All data are located in c:\grasslidar\data, unless otherwise noted.

Step 1: Creating GRASS Workspace The first thing to do when starting to work in GRASS is to create a Location. GRASS Locations are single projection areas with a defined resolution and extent. The initial location can be easily created from an existing data set.

In Windows, Click on Start-->All Programs-->GRASS GIS 7.2--> GRASS GIS 7.2 GUI

Two windows will open, the GRASS startup window ( to select or create a workspace) and the GRASS command prompt.

Initial GRASS startup screen on Windows

  • Click on the New button between the Location and Mapset windows. This will bring up the menu to define a new Location.

Location Menu 1

The GIS Data Directory is where all of your grass workspaces will reside. Creating a new directory with a unique name for grass data is recommended. This directory can be created anywhere that the user has write access. Project location is a subdirctory name for this particular project. Like with ArcGIS, it is best to avoid spaces in Directory names to avoid problems down the road. Click on the Browse button and select c:\grasslidar\grassdata. The data is from Bladen County, NC and is in the North Carolina State Plane NAD83(2011) projection with units feet, so call it bladen_stpft

  • Enter the Data Directory and Project Location – this brings up the location creation method menu

Location projection Menu 1

  • Click on the radio button for Read projection and datum terms from a georeferenced file.
  • Click Next

This brings up the georeferenced file dialog.

  • Browse to C:\grasslidar\data and look at the data available:

File data 1

In this directory, you will see 4 file types: asc, laz, tif, and vrt. LiDAR data is usually distributed as tiles of point clouds and Digital Elevation Models (DEMs) ASC and TIFF are common file formats to distribute DEM data. Asc is an ArcInfo ASCII Grid file, which is simply a text file representing a grid and does not have any projection data associated with it. Generally .tif files distributed as DEMs have projection information embedded in the file. LAZ is an open method of compression for LAS files. VRT is a virtual raster index of the 4 .tif files in this directory.

In this directory, and select D05_37_20026801_20141209.tif as the georeferenced file. 
  • Click Next.