lasFileReader

LAS or LAZ file reader

Since R2020b

Description

A lasFileReader object stores the metadata present in the LAS or LAZ file as read-only properties. The object function, readPointCloud, uses these properties to read point cloud data from the file. The lasFileReader object supports up to the LAS 1.4 specification.

A LAS file contains a public header, which has lidar metadata, followed by lidar point records. Each point record contains attributes such as 3-D coordinates, intensity, and GPS timestamp.

The LAS file format is an industry-standard binary format for storing lidar data, developed and maintained by the American Society for Photogrammetry and Remote Sensing (ASPRS). The LAZ file format is a compressed version of the LAS file format.

Creation

Syntax

lasReader = lasFileReader(fileName)

Description

lasReader = lasFileReader(fileName) creates a lasFileReader object with properties set by reading the metadata present in the LAS or LAZ file fileName. The fileName input sets the FileName property.

Properties

FileName — Name of LAS or LAZ file

character vector | string scalar

This property is read-only.

Name of the LAS or LAZ file, specified as a character vector or string scalar.

Count — Number of available point records

positive integer

This property is read-only.

Number of available point records in the file, specified as a positive integer.

LasVersion — LAS or LAZ file version

character vector

This property is read-only.

LAS or LAZ file version, specified as a character vector.

XLimits — Range of coordinates along x-axis

two-element real-valued row vector

This property is read-only.

Range of coordinates along the x-axis, specified as a two-element real-valued row vector.

YLimits — Range of coordinates along y-axis

two-element real-valued row vector

This property is read-only.

Range of coordinates along the y-axis, specified as a two-element real-valued row vector.

ZLimits — Range of coordinates along z-axis

two-element real-valued row vector

This property is read-only.

Range of coordinates along the z-axis, specified as a two-element real-valued row vector.

GPSTimeLimits — Range of GPS timestamps

1-by-2 duration vector

This property is read-only.

Range of GPS timestamp readings, specified as a 1-by-2 duration vector.

NumReturns — Maximum of all point laser returns

1 (default) | positive integer

This property is read-only.

Maximum of all point laser returns, specified as a positive integer.

NumClasses — Maximum of all point classification values

1 (default) | positive integer

This property is read-only.

Maximum of all point classification values, specified as a positive integer.

SystemIdentifier — Name of hardware sensor system identifier

string scalar

This property is read-only.

Name of the hardware sensor system identifier that generated the LAS files, specified as a string scalar.

GeneratingSoftware — Name of generating software

string scalar

This property is read-only.

Name of the generating software, specified as a string scalar. This property specifies the generating software package used when the LAS file was created.

FileCreationDate — Date of file creation

datetime object

This property is read-only.

Date of file creation, specified as a datetime object.

FileSourceID — LAS file source identifier

nonnegative integer

This property is read-only.

LAS file source identifier, specified as a nonnegative integer. Values are in the range 0 to 65535. This defines the flight line number if this file was created from an original flight line. A value 0 specifies that no ID has been assigned. Use the ProjectID and FileSourceID properties to uniquely identify each point in a LAS file.

ProjectID — Project ID

string scalar

This property is read-only.

Project ID, specified as a string scalar. This value is a globally unique identifier (GUID). Use the ProjectID and FileSourceID properties to uniquely identify each point in a LAS file.

PointDataFormat — Point data record format ID

nonnegative integer

This property is read-only.

Point data record format ID, specified as a nonnegative integer. Values are in the range 0 to 10. For more information, see Point Data Record Format.

ClassificationInfo — Classification information

table

This property is read-only.

Classification information, specified as a table. Each row of the table contains this information describing a point class:

• Classification Value — Unique classification ID number for the class, specified as a positive integer.

• Class Name — Label associated with the class, specified as a string scalar.

• Number of Points by Class — Number of points in the class, specified as a positive integer.

LaserReturnInfo — Laser return information

table

This property is read-only.

Laser return information, specified as a table. Each row of the table contains this information describing a laser return:

• Laser Return Number — Laser return number, specified as a positive integer.

• Number of Points by Return — Number of points per laser return, specified as a positive integer.

VariableLengthRecords — Variable length record information

table

This property is read-only.

Variable length record (VLR) or extended VLR information, specified as a table. Each row of the table contains this information describing a record:

• Record ID — Record identification number, specified as a positive integer.

• User ID — User identification associated with record ID, specified as a string scalar.

• Description — Description of record, specified as a string scalar.

Object Functions

readPointCloud	Read point cloud data from LAS or LAZ file
readCRS	Read coordinate reference system data from LAS or LAZ file
readVLR	Read variable length record from LAS or LAZ file
hasCRSData	Check if LAS or LAZ file has CRS data
hasGPSData	Check if LAS or LAZ file has GPS data
hasWaveformData	Check if LAS or LAZ file has waveform data
hasNearIRData	Check if LAS or LAZ file has near IR data

Examples

Read Point Cloud Data from LAZ File

This example shows how to read and visualize point cloud data from a LAS / LAZ file.

Create a lasFileReader object for a LAZ file. Then, use the readPointCloud function to read point cloud data from the LAZ file and generate a pointCloud object.

Create a lasFileReader object to access the LAZ file data.

filepath = fullfile(toolboxdir("lidar"),"lidardata", ...
    "las","aerialLidarData.laz");
lasReader = lasFileReader(filepath);

Read point cloud data from the LAZ file using the readPointCloud function.

ptCloud = readPointCloud(lasReader);

Visualize the point cloud.

figure
pcshow(ptCloud.Location)

Visualize Point Cloud Based on Classification Data from LAZ File

Segregate and visualize point cloud data based on classification data from a LAZ file.

Create a lasFileReader object to access data from the LAZ file.

path = fullfile(toolboxdir("lidar"),"lidardata", ...
    "las","aerialLidarData.laz");
lasReader = lasFileReader(path);

Read point cloud data and associated classification point attributes from the LAZ file using the readPointCloud function.

[ptCloud,pointAttributes] = readPointCloud(lasReader,"Attributes","Classification");

Color the points based on their classification attributes. Reshape the label image into the shape of the point cloud.

labels = label2rgb(pointAttributes.Classification);
colorData = reshape(labels,[],3);

Visualize the color-coded point cloud.

figure
pcshow(ptCloud.Location,colorData)

More About

Point Data Record Format

A LAS file contains point cloud data as a collection of point data records, as well as a public header block and optional metadata information about the records. The public header block indicates the point numbers and point data bounds of the LAS file, as well as the point data record format.

As of the LAS 1.4 specification, there are 11 point data record formats, ranging from Point Data Record Format 0 to Point Data Record Format 10, divided into two major groups.

• Point Data Record Format 0 to Point Data Record Format 5 — These formats contain 20 core bytes, with formats 1–5 adding optional information about GPS time, color channels, or wave packets.

• Point Data Record Format 6 to Point Data Record Format 10 — These formats contain 30 core bytes, with formats 7–10 adding optional information about color channels, near IR, or wave packets.

For more information, including which point data record formats are available for each version of the LAS file specification, see the ASPRS LASER (LAS) File Format Exchange Activities page.

Version History

Introduced in R2020b

R2022a: Object has additional properties

The lasFileReader object includes these additional properties:

• SystemIdentifier

• GeneratingSoftware

• FileCreationDate

• FileSourceID

• ProjectID

• PointDataFormat

• ClassificationInfo

• LaserReturnInfo

• VariableLengthRecords