LiDAR Tutorial using QGIS

Introduction

This tutorial aims to guide on how to access LiDAR data from the Scottish Remote Sensing Portal, download the data and visualize it in QGIS, a Geographic Information System software. This document is not intended to be a fully comprehensive guide but a brief overview and a pointer to further resources.

LiDAR

LiDAR stands for Light Detection and Ranging and is an active remote sensing technique that records the earth surface. The LiDAR sensor emits pulses of laser and measures properties of the reflected light - the timings, the angles and the wavelengths. The integration of GNSS (Global Navigation Satellite System) permits to accurately define the location (XYZ coordinates) of the point from which the signal was returned.
In addition to geographic position other attributes of the LiDAR points can be recorded, for example, intensity, classification, RGB values, number of returns or scan angle. Although, not always all the attributes are provided to the end-users.

LAS and LAZ files

LiDAR points XYZ measurement, attributes and other metadata are stored in LAS files, an open format considered to be an industry standard. LAZ files are compressed LAS files.

Digital Elevation Models

Digital Surface Model (DSM) is a numeric representation of the earth surface produced from the first return of laser signal. DSM includes objects on its surface such as vegetation or buildings.

Digital Terrain Model (DTM) is a numeric representation of the earth surface produced from the last return of laser signal. DTM shows the bear earth with vegetation and buildings removed.

Scottish Remote Sensing Portal

Scottish Government and JNCC collaborate to develop an online data portal to host public sector LiDAR datasets. The Scottish Remote Sensing Portal currently provides access to three sets of Scottish public sector airborne LiDAR data, which can be downloaded as 10km tiles or accessed via Web Map Services (WMS). The data are provided as point clouds (LAZ) and raster files (GeoTIFF) All data are shared under the Open Government License v3 unless otherwise stated.
The Scottish Remote Sensing Portal can be accessed following this link https://remotesensingdata.gov.scot/.

QGIS

QGIS is a free and open-source Geographic Information System created to view, edit and analyse geospatial data. The software can be freely downloaded from the project website - https://qgis.org/en/site/index.html - and installed on various platforms including Windows, Linux and Mac OSX.

If you are not familiar with the software it is recommended that you familiarize yourself with the documentation section - https://qgis.org/en/docs/index.html

Downloading Data

Scottish LiDAR data can be downloaded directly from the Scottish Remote Sensing Portal. The portal provides Graphical User Interface (GUI) in the form of an interactive map. The user can specify the area of interest by manipulating the size and location of a blue rectangle. Once the location is specified, the left panel will display available datasets within the area. The user can then select between LAZ, DTM and DSM files. Next, the user can select particular tiles by highlighting and clicking on a grid square on the map or tile name on the right-hand panel. The selection then is added to the shopping basket and available in the Download tab. Finally, each file needs to be downloaded separately by clicking the Download button. The files are compressed as ZIP files and have to be extracted before loading them into QGIS.
In our example, we have downloaded a file called NX6055_4PPM_LAS_PHASE3.LAZ into a data folder.



Workings with LAZ

Open the file

Once the LAZ file is downloaded and extracted it can be opened in QGIS.

  • open a new project in QGIS
  • open Data Source Manager and select Point Cloud tab
  • navigate to the LAZ file location and add to the map view
  • alternatively you can drag and drop the file from the file browser


After adding the file QGIS will create a new sub-directory for EPT files indexing the LiDAR points. As a result, when panning and zooming QGIS will render only a subset of points for better performance.

Check CRS

Point Cloud should have Coordinate Reference System (CRS) assigned but it is not always a case and sometimes we have to specify the projection manually.

  • right-click on the question mark next to the filename
  • specify the CRS to OSGB 1936 / British National Grid (EPSG:27700)


Investigate Attributes

Once the file is loaded QGIS is looking at the attributes stored in the point cloud to apply appropriate colouring. In our example, the points are visualized based on the classification (Ground, Vegetation, Building, and so on)



The Identify Map Tool can be used to investigate further information about specific point attributes e.g. XYZ or Intensity.



The Layer Styling Panel allows changing the point visualization using the additional attributes.

  • in the panel change the rendering from Classification to Attribute by Ramp

  • select the Z value to shade the points based on their height



The summary statistics of the attributes can be accessed in the layer properties.

  • right-click on the file in the Table of Contents (TOC)

  • select Properties and click on the Statistics tab

3D map view

QGIS can also visualize the points in 3 dimensions.

  • go to View and select New 3D Map View

  • go to Layer Styling Panel and select the 3D View Tab - change the rendering to Attribute by Ramp and Attribute to z

  • in the same Layer Styling Panel select Symbology and change rendering to Extent Only

  • use the navigation tools in 3D view to zoom and rotate the scene



It is possible to achieve more realistic rendering of the terrain by clicking on the Options and selecting Show Eye Dome Lightning.



Working with Raster

FAQ