Header · LASDatasets.jl

Each LAS file starts with a block of header information that contains metadata for the whole file. LASDatasets.jl uses the LasHeader struct to wrap around this data and defines a user-friendly interface to modify certain aspects of it.

LASDatasets.LasHeader — Type

mutable struct LasHeader

A LAS Header containing metadata regarding information in a LAS file See full specification here

las_version::VersionNumber: The LAS spec version this header was written in
file_source_id::UInt16: Numeric identifier for the source that made this file. Set to 0 if the ID is unassigned
global_encoding::UInt16: A bit field used to indicate global properties. See the spec for more info
guid_1::UInt32: First member of the Project GUID
guid_2::UInt16: Second member of the Project GUID
guid_3::UInt16: Third member of the Project GUID
guid_4::NTuple{8, UInt8}: Fourth member of the Project GUID
system_id::NTuple{32, UInt8}: A unique identifier indicating how the data was created
software_id::NTuple{32, UInt8}: Identifier for the software that created the LAS file
creation_dayofyear::UInt16: The Greenwich Mean Time (GMT) day of the year (as an unsigned short) on which the file was created
creation_year::UInt16: Four digit number for the year the file was created
header_size::UInt16: Size (in bytes) of the public header block in the LAS file. This varies depending on which LAS version was used to write it. For LAS v1.4 it's 375 bytes
data_offset::UInt32: Offset to the point data (in bytes) from the start of the file to the first field of the first point record
n_vlr::UInt32: Number of Variable Length Records (VLR's) in the LAS file. These come after the header and before the point records
data_format_id::UInt8: Point data record format stored in the LAS file. LAS v1.4 supports formats 0-10
data_record_length::UInt16: Size in bytes of a point data record
legacy_record_count::UInt32: For maintaining legacy compatibility, the number of point records in the file (must not exceed typemax(UInt32)). Only populated for point records 0-5
legacy_point_return_count::NTuple{5, UInt32}: For maintaining legacy compatibility, the number of points per return (max of 5 returns, counts must not exceed typemax(UInt32)). Only populated for point records 0-5
spatial_info::SpatialInfo: Spatial information describing the bounding range of the points, their offsets and any scaling factor applied to them
waveform_record_start::UInt64: Offset in bytes from the start of the file to the first byte of the Waveform Data Package Reckord
evlr_start::UInt64: Offset in bytes from the start of the file to the first byte of the first Extended Variable Length Record (EVLR)
n_evlr::UInt32: Number of EVLR's in the LAS file
record_count::UInt64: Number of point records saved in this file (can't exceed typemax(UInt64)). This is populated for LAS v1.4
point_return_count::NTuple{15, UInt64}: Number of points per return saved in this file (15 returns total, counts can't exceed typemax(UInt64)). This is populated for LAS v1.4

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You can access information from the header using any of the following functions:

LASDatasets.las_version — Function

las_version(h::LasHeader) -> VersionNumber

Get the LAS specification version from a header h

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LASDatasets.file_source_id — Function

file_source_id(h::LasHeader) -> UInt16

Get the file source ID specification version from a header h

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LASDatasets.global_encoding — Function

global_encoding(h::LasHeader) -> UInt16

Get the global properties bit vector from a header h

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LASDatasets.system_id — Function

system_id(h::LasHeader) -> String

Get the system ID from a header h

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LASDatasets.software_id — Function

software_id(h::LasHeader) -> String

Get the software ID from a header h

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LASDatasets.creation_day_of_year — Function

creation_day_of_year(h::LasHeader) -> UInt16

Get the creation day of the year from a header h

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LASDatasets.creation_year — Function

creation_year(h::LasHeader) -> UInt16

Get the creation year from a header h

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LASDatasets.header_size — Function

header_size(h::LasHeader) -> Int64

Get the size of a header h in bytes

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LASDatasets.point_data_offset — Function

point_data_offset(h::LasHeader) -> Int64

Get the offset to the first point record in a LAS file specified by a header h

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LASDatasets.point_record_length — Function

point_record_length(h::LasHeader) -> Int64

Get the number of bytes assigned to each point record in a LAS file specified by a header h

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LASDatasets.point_format — Function

point_format(header::LasHeader) -> Any

Get the LAS point format from a header header

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LASDatasets.number_of_points — Function

number_of_points(h::LasHeader) -> Int64

Get the number of points in a LAS file from a header h

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LASDatasets.get_number_of_points_by_return — Function

get_number_of_points_by_return(
    header::LasHeader
) -> Union{NTuple{5, UInt32}, NTuple{15, UInt64}}

Get the number of points per return for a header header

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LASDatasets.number_of_vlrs — Function

number_of_vlrs(h::LasHeader) -> Int64

Get the number of Variable Length Records in a LAS file from a header h

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LASDatasets.number_of_evlrs — Function

number_of_evlrs(h::LasHeader) -> Int64

Get the number of Extended Variable Length Records in a LAS file from a header h

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LASDatasets.evlr_start — Function

evlr_start(header::LasHeader) -> UInt64

Get the offset in bytes to the first EVLR in a LAS file from a header header

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LASDatasets.spatial_info — Function

spatial_info(h::LasHeader) -> SpatialInfo

Get the spatial information for point positions in a LAS file from a header h. This includes the offsets/scale factors applied to points and bounding box information

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LASDatasets.num_return_channels — Function

num_return_channels(h::LasHeader) -> Int64

Get the number of return channels in a LAS file from a header h

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LASDatasets.is_standard_gps — Function

If true, GPS Time is standard GPS Time (satellite GPS Time) minus 1e9. If false, GPS Time is GPS Week Time.

Note that not all software sets this encoding correctly.

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LASDatasets.is_wkt — Function

Check if the projection information is in WKT format (true) or GeoTIFF (false)

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LASDatasets.is_internal_waveform — Function

is_internal_waveform(header::LasHeader) -> Bool

Returns whether a LAS file with header header has waveform data stored in the LAS file

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LASDatasets.is_external_waveform — Function

is_external_waveform(header::LasHeader) -> Bool

Returns whether a LAS file with header header has waveform data in an external file

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LASDatasets.waveform_record_start — Function

waveform_record_start(header::LasHeader) -> UInt64

Get the offset in bytes to the first waveform record for a LAS file with header header

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You can also modify certain fields in the header, but one should note that for some of these fields, such as those impacting the byte layout of the LAS file itself, it's better to let the system do it automatically so that your header remains consistent with your dataset.

set_las_version!(h::LasHeader, v::VersionNumber)

Set the LAS specification version in a header h to version v

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set_point_format!(h::LasHeader, _::Type{TPoint<:LasPoint})

Set the point format in a header h to a new value, TPoint

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set_spatial_info!(
    header::LasHeader,
    info::SpatialInfo
) -> SpatialInfo

Set the spatial information associated to points in a LAS file with a header header

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set_point_data_offset!(
    header::LasHeader,
    offset::Integer
) -> UInt32

Set offset to the first point record in a LAS file with a header header

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set_point_record_length!(
    header::LasHeader,
    length::Integer
) -> UInt16

Set the number of bytes associated to each point record in a LAS file with a header header

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set_point_record_count!(
    header::LasHeader,
    num_points::Integer
)

Set the number of points in a LAS file with a header header

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set_num_vlr!(header::LasHeader, n::Integer) -> UInt64

Set the number of Variable Length Records in a LAS file with a header header

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set_num_evlr!(header::LasHeader, n::Integer) -> UInt64

Set the number of Extended Variable Length Records in a LAS file with a header header

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set_gps_week_time_bit!(header::LasHeader) -> UInt16

Sets the bit flag indicating that the header header is in GPS week time

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set_gps_standard_time_bit!(header::LasHeader) -> UInt16

Sets the bit flag indicating that the header header is in GPS standard time

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set_waveform_internal_bit!(header::LasHeader) -> UInt16

Sets the bit flag indicating that the header header has internal waveform records

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set_waveform_external_bit!(header::LasHeader) -> UInt16

Sets the bit flag indicating that the header header has external waveform records

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set_synthetic_return_numbers_bit!(
    header::LasHeader
) -> UInt16

Sets the bit flag indicating that the header header has synthetically-generated return numbers

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unset_synthetic_return_numbers_bit!(
    header::LasHeader
) -> UInt16

Sets the bit flag indicating that the header header does not have synthetically-generated return numbers

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set_wkt_bit!(header::LasHeader) -> UInt16

Sets the bit flag indicating that the LAS file with header header has its coordinate reference system set as a WKT

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unset_wkt_bit!(header::LasHeader) -> UInt16

Sets the bit flag indicating that the LAS file with header header doesn't have its coordinate reference system set as a WKT

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set_number_of_points_by_return!(
    header::LasHeader,
    points_per_return::NTuple{N, Integer}
)

Set the number of points per return for a header header to the values points_per_return

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