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Product Affected: MapInfo Pro™
What is LiDAR?LiDAR (Light Detection and Ranging), a remote sensing method, uses light in the form of a pulsed laser to measure ranges (variable distances) to the Earth. These light pulses when combined with various datasets recorded by the airborne system generate precise, three-dimensional (3D) information about the shape and surface characteristics of the Earth (NOAA).
There are two major types of LiDAR
- Topographic: Used for mapping land through near-infrared laser
- Bathymetric: Used to measure sea-floor and river bed elevations through water penetrating green light
LiDAR attributesVarious attributes are maintained with LiDAR point datasets along with from x, y and z values. Table 1 describes the attributes that are recorded for each laser pulse and provided with each LiDAR point.
|Elevation (Z)||Elevation values of point density cloud|
|Intensity||Return strength of the laser pulse that generated the LiDAR point|
|Return number||An emitted laser pulse can have various levels of returns depending on the features it is reflected from and the capabilities of the laser scanner used to collect the data. The first return is flagged as return number one, the second as return number two, and so on.|
|Number of returns||The number of returns is the total number of returns for a given pulse.|
|Classification||Every LiDAR point that is post-processed can have a classification that defines the type of object that has reflected the laser pulse. LiDAR points can be classified into a number of categories including bare earth or ground, top of canopy, and water. The different classes are defined using numeric integer codes in the LAS files.|
|Scan angle||Scan angle is a value in degrees between -90 and +90. At 0 degrees, the laser pulse is directly below the aircraft at nadir. At -90 degrees, the laser pulse is to the left side of the aircraft, while at +90, the laser pulse is to the right side of the aircraft in the direction of flight. Most LiDAR systems are currently less than ±30 degrees.|
|Point Source ID||Identification number of point dataset|
|GPS Time||The GPS time stamp at which the laser point was emitted from the aircraft. The time is in GPS seconds of the week.|
What are different LIDAR data types?LiDAR dataset can be stored in various formats. The native data are delivered as points (point clouds) which can be used to generate elevation models (Digital Elevation Models) or create Triangulated Irregular Network surfaces (TINs). These surfaces can be used to generate contours (line joining point of equal height).
PointPoints Point data are stored in LAS format, which “is a binary file format that maintains information specific to the LIDAR nature of the data while not being overly complex” (ASPRS, 2007). These point cloud contains information such as the number of returns, intensity of the returns, classification, the source (flight line) of each point, the time apart from x, y, and z values.
Surface: Digital Elevation Models (DEMs) or Triangulated Irregular Networks (TINs)Surface models such as DEMs and TINs can be generated from point cloud data based on through interpolation techniques such as Nearest Neighbor, Inverse distance, minimum curvature, natural neighbors etc. The appropriate interpolation method depends on the data and the desired use of the DEM. Figure 1 illustrates surface generated based on height values (Z) of the point cloud data using MapInfo Pro Raster.
Figure 1: Surface generated based on height values (Z) of the point cloud data
What is LAS format?The LAS file format is a public file format for the interchange of 3-dimensional point cloud data between data users. Although developed primarily for exchange of LiDAR point cloud data, this format supports the exchange of any 3-dimensional x,y,z tuplet (ASPRS, 2007).
LAS file can be easily imported using MapInfo Raster and surface can be generated on various LiDAR attributes such as elevation, intensity, return numbers etc.
Where can I obtain free LIDAR data?LIDAR datasets are available from various public and private entities and can be obtained free, or at a cost. A few sources for obtaining free LIDAR datasets are enlisted below:
- USGS Earth Explorer https://earthexplorer.usgs.gov/
- NOAA’s Digital Coast Data Access Viewer - https://coast.noaa.gov/dataviewer/#/LiDAR/search/
- United States Interagency Elevation Inventory https://coast.noaa.gov/inventory/
- Open Topography - http://opentopo.sdsc.edu/datasets?listAll=true
- Centre for the Environmental Data Archival (CEDA) http://www.ceda.ac.uk
- GIPUZKOA.NET (SPAIN) ftp://ftp.geo.euskadi.net/LiDAR/
What applications are there for LiDAR data?LiDAR datasets are now used everywhere. These dataset allows examining both natural and manmade environments with accuracy, precision, and flexibility. LIDAR dataset accuracy and precision enables to supports activities such as risk modelling, vulnerability analysis, forest characterization, urban planning, flood forecasting, geomorphic mapping and many more. A few of the LIDAR applications is listed which can easily analyzed in MapInfo Pro Raster.
Forestry Management and PlanningLiDAR datasets help in measurement of tree canopies as well as mapping the ground beneath the tree. The dataset can be used identify trees, tree types, canopy size, density and canopy base height. Various information obtained can be used for, fire risk modelling, forest planning or to estimate the root expanse which could help insurers when considering house premium in particular region.
Precision Farming/AgricultureLiDAR dataset can be used to create topographical map of the fields and help in precision farming such as which area need to be supplied with fertilizers if sun exposure is low, or which area require more water by analyzing slope profile from LiDAR surface.
Vulnerability Analysis and Risk ModellingLiDAR data helps in detecting faults and for measuring surface uplifts. The matrix based on proximity of faults, surface uplifts etc. can help in performing vulnerability analysis of a region. Vulnerability is also an important parameter of risk modelling. For example flood modelling: Features such as buildings, river banks or constructed roads have a great effect on flow dynamics and flood propagation. LiDAR has brought feature level details which allow much more accurate flood prediction models to be created.
Urban PlanningLiDAR dataset can be easily used to obtain Digital Surface Models (DSMs) of the earth's surface which when combine with aerial photographs or orthophotos can be used create digital City Models. These city models can be used for planning such as solar panel placements for power generation, land-use planning building and its amenities mapping etc.
Cartographic MappingLiDAR assists in road, building and vegetation mapping due to its high resolution and accuracy. Used in conjunction with aerial photography. The 3D aspect of LiDAR makes it especially suitable for mapping terrain models, deriving high-resolution contour maps, profile, curvatureof a topography for various uses.
UPDATED: August 7, 2019