lidarPointAttributes
Description
The lidarPointAttributes
object stores additional point
attributes that are not stored in a pointCloud
object. These attributes are
associated to lidar data.
Creation
Use either lidarPointAttributes
function or the
readPointCloud
function to create a
lidarPointAttributes
object. The readPointCloud
function also creates a pointCloud
object.
To create a lidarPointAttributes
object using
readPointCloud
function, see the Read Attributes from LAS File example.
Description
creates a attr
= lidarPointAttributes(Name=Value
)lidarPointAttributes
object with properties set using one or
more name-value arguments.
Properties
Count
— Number of available point records in file
nonnegative integer
This property is read-only.
Number of available point records in the file, specified as a nonnegative integer.
Classification
— Classification numbers
[]
(default) | M-by-1 vector of nonnegative integers
Classification numbers of each point, specified as an M-by-1 vector of nonnegative integers. M is equal to the number of available point records.
For LAS file point data record formats 0 to 5, the classification number ranges from 0 to 31.
Classification Number | Classification Type |
---|---|
0 | Created, never classified |
1 | Unclassified |
2 | Ground |
3 | Low vegetation |
4 | Medium vegetation |
5 | High vegetation |
6 | Building |
7 | Low point (noise) |
8 | Model key-point |
9 | Water |
10 | Reserved |
11 | Reserved |
12 | Overlap points |
13 - 31 | Reserved |
For LAS file point data record formats 6 to 10, the classification number ranges from 0 to 255.
Classification Number | Classification Type |
---|---|
0 | Created, never classified |
1 | Unclassified |
2 | Ground |
3 | Low vegetation |
4 | Medium vegetation |
5 | High vegetation |
6 | Building |
7 | Low point (noise) |
8 | Reserved |
9 | Water |
10 | Rail |
11 | Road surface |
12 | Reserved |
13 | Wire guard (shield) |
14 | Wire conductor (phase) |
15 | Transmission tower |
16 | Wire-structure connector (insulator) |
17 | Bridge deck |
18 | High noise |
19
| Overhead structure |
20 | Ignored ground |
21 | Snow |
22 | Temporal exclusion |
23 - 63 | Reserved |
64 - 255 | User-defined |
These are standard class names and class-object mappings. The class definition and mapping might differ depending on the application that created the LAS or LAZ file.
Example: Classification
=[0 255 128]'
specifies
the classification numbers for three points as 0, 255, and 128.
Data Types: uint8
LaserReturn
— Laser pulse return numbers
[]
(default) | M-by-1 vector of positive integers
Laser pulse return numbers of each point, specified as an M-by-1 vector of positive integers. M is equal to the number of available point records.
For LAS file point data record formats 0 to 5, the values are in the range 1 to 5, and for point data record formats 6 to 10, the values are in the range 1 to 15.
Example: LaserReturn
=[10 15 1]'
specifies the
laser pulse return numbers for three points as 10, 15, and 1.
Data Types: uint8
NumReturns
— Total number of returns
[]
(default) | M-by-1 vector of positive integers
Total number of returns for a pulse, specified as an M-by-1 vector of positive integers. M is equal to the number of available point records.
For LAS file point data record formats 0 to 5, the values are in the range 1 to 5, and for point data record formats 6 to 10, the values are in the range 1 to 15.
Example: NumReturns
=[1 10 15]'
specifies the
total number of returns for three points as 1, 10, and 15.
Data Types: uint8
GPSTimeStamp
— GPS time stamps
[]
(default) | M-by-1 duration
vector
GPS time stamps of each point, specified as an M-by-1 duration
vector in seconds. M is equal to the number of
available point records.
Example: GPSTimeStamp
=seconds(1:3)'
specifies
the GPS time stamps for three points as 1, 2, and 3 seconds.
NearIR
— Near infrared channel value
[]
(default) | M-by-1 vector of positive integers
Near infrared channel value of each point, specified as an M-by-1 vector of positive integers. M is equal to the number of available point records. Values must be in the range [0, 65535].
Example: NearIR
=ones(3,1)
specifies the near
infrared channel values for three points as 1
.
Data Types: uint16
ScanAngle
— Scan angle
[]
(default) | M-by-1 vector
Scan angle of each point, specified as an M-by-1 vector. Each value represents the rotational angle at which the point is captured in the laser system. The angle is negative to the left of the front of the sensor, positive to the right, and 0 degrees directly in front. M is equal to the number of available point records.
For LAS file point data record formats 0 to 5, the values are in the range –90 to 90, and for point data record formats 6 to 10, the value ranges from –180 to 180.
Example: ScanAngle
=[0 -180 105]'
specifies the
scan angles for three points as directly ahead, 180 degrees to the left, and 105 degrees
to the right.
Data Types: single
PointSourceID
— Point source ID
[]
(default) | M-by-1 vector of nonnegative integers
Point source ID of each point, specified as an M-by-1 vector of nonnegative integers. Each element defines the source from which a point originates. M is equal to the number of available point records.
A source is a grouping of temporally consistent data, such as a flight line for aerial systems. The values are in the range [0, 65535].
Example: PointSourceID
=[0 1 65535]'
specifies
the point source IDs for three points as 0, 1, and 65535.
Data Types: uint16
ScannerChannel
— Scanner channel
[]
(default) | M-by-1 vector of nonnegative integers
Scanner channel of each point, specified as an M-by-1 vector of nonnegative integers. M is equal to the number of available point records.
For single channel systems the value is 0
. The values are in the
range [0, 3].
Example: ScannerChannel
=[0 0 0]'
specifies the
scanner channels for three points as 0
.
Data Types: uint8
ScanDirectionFlag
— Scan direction flag
[]
(default) | M-by-1 logical vector
Scan direction flag of each point, specified as an M-by-1 logical vector. M is equal to the number of available point records.
The value specifies the direction of scanner mirror motion during the capture of the
corresponding point. Left-to-right motion is defined as positive, while right-to-left
motion is defined as negative. A logical 1
(true
)
denotes a positive scan direction for the point, and a logical 0
(false
) denotes a negative scan direction.
Example: ScanDirectionFlag
=false(3,1)
specifies
the scan direction flags for three points as right-to-left.
Data Types: logical
EdgeOfFlightLineFlag
— Edge of flight line flag
[]
(default) | M-by-1 logical vector
Edge of flight line flag of each point, specified as an M-by-1 logical vector. M is equal to the number of available point records.
Logical 1
(true
) indicates that the point lies
on the edge of the flight line. Otherwise, the corresponding element is a logical
0
(false
).
Example: EdgeOfFlightLineFlag
=true(3,1)
specifies that three points lie on the edge of the flight line.
Data Types: logical
ClassificationFlags
— Classification flags
empty structure (default) | structure
Classification flags, specified as a structure. The structure contains these fields:
Synthetic
— An M-by-1 logical vector, where logical1
(true
) indicates that the point was generated synthetically. Otherwise, the point is specified as logical0
(false
).Keypoint
— An M-by-1 logical vector, wheretrue
indicates that the point is a model key-point. Otherwise, the point is specified asfalse
.Withheld
— An M-by-1 logical vector, wheretrue
indicates that the point is withheld from the processing algorithm. Otherwise, the point is specified asfalse
.Overlap
— An M-by-1 logical vector, wheretrue
indicates that the point lies within the overlap region of two or more swaths. Otherwise, the point is specified asfalse
.
Example: ClassificationFlags
=struct(Synthetic=true(3,1),Keypoint=false(3,1),Withheld=true(3,1),Overlap=false(3,1))
specifies the classification flags for three points as a structure.
WaveformData
— Waveform data
empty structure (default) | structure
Waveform data, specified as a structure. The waveform data is stored in point records and the corresponding variable length records of a LAS or LAZ file. The structure contains these fields:
Field | Value | Description |
---|---|---|
WavePacketDescriptorIndex | M-by-1 vector of type double | If this value is greater than zero, then the corresponding point has waveform information in the VLR record indicated by the value of this field + 99. When this value is zero, the point has no waveform data. |
ByteOffsetToWaveformPacketData | M-by-1 vector of type double | Defines the location of the waveform packet of a particular point within the stored waveform data. This data is present in an extended variable length record (EVLR) or an auxiliary WPD file. |
WaveformPacketSize | M-by-1 vector of type double | Defines the size of waveform packet in bytes. This value is present in an extended variable length record (EVLR) or an auxiliary WPD file. |
ReturnPointLocation | M-by-1 vector of type double | Each element represents the offset from the first digitized value to the location within the waveform packet at which the associated return pulse was detected. These values are represented in picoseconds. |
Xt | M-by-1 vector of type double | Defines the X component of parametric line equation. For more information, see Parametric line equation. |
Yt | M-by-1 vector of type double | Defines the Y component of parametric line equation. For more information, see Parametric line equation. |
Zt | M-by-1 vector of type double | Defines the Z component of parametric line equation. For more information, see Parametric line equation. |
BitsPerSample | M-by-1 vector of type double | Number of bits for each sample in the range 2 to 32 bits. |
CompressionType | M-by-1 vector of type double | Compression algorithm for waveform packets. Value 0 represents no compression. Reserved for future use. |
NumberOfSamples | M-by-1 vector of type double | Defines the number of samples in decompressed waveform packet. |
TemporalSpacing | M-by-1 vector of type double | Defines the temporal sample spacing in picoseconds. |
DigitizerGain | M-by-1 vector of type double | Defines the digitizer gain to use to convert raw digitized value to an absolute digitizer voltage. |
DigitizerOffset | M-by-1 vector of type double | Defines the digitizer offset to use to convert raw digitized value to an absolute digitizer voltage. |
This example specifies the waveform data for three points as a structure.
WaveformData = struct(WavePacketDescriptorIndex=[2011 2200 3215]', ... ByteOffsetToWaveformPacketData=[51 65 78]', ... WaveformPacketSize=[12 28 25]', ... ReturnPointLocation=[1 2 3]', ... Xt=[1 2 3]',Yt=[3 4 5]',Zt=[5 6 7]', ... BitsPerSample=[1 2 3]', ... CompressionType=[1 0 1]', ... NumberOfSamples=[10 25 32]', ... TemporalSpacing=[11 21 31]', ... DigitizerGain=[11 12 13]', ... DigitizerOffset=[21 22 23]')
UserData
— User data
[]
(default) | M-by-1 vector of integers
User data, specified as an M-by-1 vector of integers. M is equal to the number of available point records. This value corresponds to the user data field of the point record data in the LAS file. Use this field at your discretion.
Example: UserData
=[1 2 4]'
specifies the user
data for three points.
Object Functions
select | Select subset of lidar point attributes |
concatenate | Concatenate lidar point attributes array |
Examples
Read Attributes from LAS File
Create a lasFileReader
object for a LAS file. Then, use the readPointCloud
function to read attributes from the LAS file and generate a lidarPointAttributes
object.
Create a lasFileReader
object to access the LAS file data.
path = fullfile(toolboxdir("lidar"),"lidardata", ... "las","aerialLidarData2.las"); lasReader = lasFileReader(path);
Read all points and point attributes from the LAS file to a pointCloud
object and lidarPointAttributes
object, respectively, by using the readPointCloud
function.
[ptCloud,pointAttributes] = readPointCloud(lasReader,Attributes= ... ["Classification","LaserReturn","NumReturns", ... "EdgeOfFlightLine","ScanAngle"]);
Display the point attributes.
disp(pointAttributes)
lidarPointAttributes with properties: Count: 78970 Classification: [78970x1 uint8] LaserReturn: [78970x1 uint8] NumReturns: [78970x1 uint8] GPSTimeStamp: [0x0 duration] NearIR: [] ScanAngle: [78970x1 single] PointSourceID: [] ScannerChannel: [] ScanDirectionFlag: [] EdgeOfFlightLineFlag: [78970x1 logical] ClassificationFlags: [1x1 struct] WaveformData: [1x1 struct] UserData: []
Create lidarPointAttributes
Object
Specify attributes of the lidarPointAttributes
object for three points.
classificationValues=[0 255 128]'; laserReturns=[10 15 1]'; numReturns=[1 10 15]';
Create a lidarPointAttributes
object.
attr=lidarPointAttributes(Classification=classificationValues, ...
LaserReturn=laserReturns,NumReturns=numReturns);
Display the point attributes.
disp(attr)
lidarPointAttributes with properties: Count: 3 Classification: [3x1 uint8] LaserReturn: [3x1 uint8] NumReturns: [3x1 uint8] GPSTimeStamp: [0x0 duration] NearIR: [] ScanAngle: [] PointSourceID: [] ScannerChannel: [] ScanDirectionFlag: [] EdgeOfFlightLineFlag: [] ClassificationFlags: [1x1 struct] WaveformData: [1x1 struct] UserData: []
Algorithms
The values of Xt
, Yt
, and Zt
fields in WaveformData
property define a parametric line equation for
extrapolating points along the associated waveform. The position along the wave is given by:
where X, Y, and Z represent the spatial position of the derived point, X0, Y0, and Z0 define the position of the anchor point, Xt, Yt, and Zt define the position of the point at a distance of time t, in picoseconds, relative to the anchor point. The X, Y, and Z units are identical to the units of the coordinate system of the LAS data. If the coordinate system is geographic, the horizontal units are decimal degrees and the vertical units are in meters.
The fields Xt
, Yt
, and Zt
have
been renamed to dx
, dy
, and dz
in
latest LAS file specification. For more information, see the ASPRS LASER (LAS) File Format Exchange Activities page.
Version History
Introduced in R2022aR2024a: select
and concatenate
object functions
The lidarPointAttributes
object has these new object functions:
select
— Select subset of lidar point attributesconcatenate
— Concatenate lidar point attributes
R2022b: WaveformData
property has additional fields
The structure for the WaveformData
property has these additional fields.
WavePacketDescriptorIndex
ByteOffsetToWaveformPacketData
WaveformPacketSize
R2022b: WaveformData
structure fields are updated
The order of fields in the WaveformData
structure has been updated
to:
WavePacketDescriptorIndex: [] ByteOffsetToWaveformPacketData: [] WaveformPacketSize: [] ReturnPointLocation: [] Xt: [] Yt: [] Zt: [] BitsPerSample: [] CompressionType: [] NumberOfSamples: [] TemporalSpacing: [] DigitizerGain: [] DigitizerOffset: []
Prior to R2022b, the order was:
Xt: [] Yt: [] Zt: [] ReturnPointLocation: [] BitsPerSample: [] CompressionType: [] NumberOfSamples: [] TemporalSpacing: [] DigitizerGain: [] DigitizerOffset: []
See Also
Functions
Objects
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