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LAS file format
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| LAS | |
|---|---|
| Filename extension |
.las |
| Internet media type | application/vnd.las |
| Magic number | LASF |
| Developed by | American Society for Photogrammetry and Remote Sensing |
| Initial release | May 9, 2003 |
| Latest release | 1.4 R15 July 9, 2019 |
| Type of format | Point cloud data |
| Open format? | Yes |
The LAS (LASer) format is a file format designed for the interchange and archiving of Lidar point cloud data. It is an open, binary format specified by the American Society for Photogrammetry and Remote Sensing (ASPRS). The format is widely used[1] and regarded as an industry standard for Lidar data.[2][3]
File structure
[edit]A LAS file consists of the following overall sections:
| Section | Description |
|---|---|
| Public header block | Describes format, number of points, extent of the point cloud and other generic data. |
| Variable length records (VLR) | Any number of optional records to provide various data such as the spatial reference system used, metadata, waveform packet information and user application data.[1][4] Each VLR can hold a data payload of up to 65,535 bytes in length. |
| Point data records | Data for each of the individual points in the point cloud, including coordinates, classification (e.g. terrain or building), flight and scan data, etc. |
| Extended variable length records (EVLR) | Introduced with LAS 1.3,[5] EVLRs are similar to VLRs but are located after the point data records and allow a much larger data payload per record due to the use of 8-byte size descriptors. |
Point data records
[edit]A LAS file contains point records in one of the point data record formats defined by the LAS specification; as of LAS 1.4, there are 11 point data record formats (0 through 10) available. All point data records must be of the same format within the file. The various formats differ in the data fields available, such as GPS time, RGB and NIR color and wave packet information.
The 3D point coordinates are represented within the point data records by 32-bit integers, to which a scaling and offset defined in the public header must be applied in order to obtain the actual coordinates.
As the number of bytes used per point data record is explicitly given in the public header block, it is possible to add user-defined fields in "extra bytes" to the fields given by the specification-defined point data record formats. A standardized way of interpreting such extra bytes was introduced in the LAS 1.4 specification, in the form of a specific EVLR.[4]
Derivative formats
[edit]LAZ
[edit]LAZ is an open format for lossless compression of LAS files developed by Martin Isenburg, author of its original LASzip reference implementation.[6][7][8] The size of a LAZ file is typically 7 to 25 percent of the corresponding LAS file, and it has become a de facto industry standard for compressed point cloud data.[9]
LAZ files are similar in structure to the corresponding uncompressed LAS files, except the point data records are replaced by chunks of compressed point data.[10]
LASzip was originally published under the GNU LGPL, but relicensed under the Apache Public License 2.0 in late 2021.[11] Alternative LAZ implementations include LAZperf[12] and laz-rs.[13]
COPC
[edit]The Cloud Optimized Point Cloud (COPC) format specified by Hobu, Inc.[14] is a cloud-optimized variant of LAZ, analogous to the COG format's relationship to GeoTIFF.[15] A COPC file guarantees a restricted structure of the LAZ file to make its data chunks correspond to nodes in an octree, making the file suitable for subset requests.
References
[edit]- ^ a b "LAS (LASer) File Format, Version 1.4". Library of Congress. 2015-01-14. Retrieved 2019-01-12.
- ^ "About Point Clouds and LiDAR Data". Autodesk Knowledge Network. Autodesk. 2018-05-01. Retrieved 2019-01-12.
- ^ "What is a LAS dataset?". Esri. Retrieved 2019-01-12.
- ^ a b "LAS specification, version 1.4 – R13" (PDF). American Society for Photogrammetry and Remote Sensing. 2013-07-15. Retrieved 2019-01-12.
- ^ "LAS specification, version 1.3 – R11" (PDF). American Society for Photogrammetry and Remote Sensing. 2010-10-24. Retrieved 2019-01-12.
- ^ "LASzip - free and lossless LiDAR compression". rapidlasso GmbH. Retrieved 2025-05-25.
- ^ Isenburg, Martin (November 2011). LASzip: lossless compression of LiDAR data (PDF) (Technical report). rapidlasso GmbH. Retrieved 2025-05-25.
- ^ Isenburg, Martin. "Homepage of Martin Isenburg". The University of North Carolina at Chapel Hill. Archived from the original on 2025-03-16. Retrieved 2025-05-25.
- ^ "OGC considers LAZ 1.4 as Community Standard". Open Geospatial Consortium. 2025-02-13. Retrieved 2025-05-26.
- ^ Eickenberg, Björn (2024-10-27). "5.1. Overview". LAZ Specification 1.4 (PDF) (Technical report). rapidlasso GmbH. Retrieved 2025-05-25.
- ^ Isenburg, Dieter (2021-10-18). "LASzip Apache Software License version 2.0 grant" (PDF). rapidlasso.de. Retrieved 2025-05-26.
- ^ "laz-perf". GitHub. Hobu, Inc. Retrieved 2025-05-25.
- ^ "laz-rs". GitHub. Retrieved 2025-05-25.
- ^ "Cloud Optimized Point Cloud Specification – 1.0". Hobu, Inc. 2021. Retrieved 2025-05-25.
- ^ "Cloud-Optimized Point Clouds (COPC)". Cloud-Optimized Geospatial Formats Guide. Cloud-Native Geospatial Foundation. Retrieved 2025-05-25.
External links
[edit]LAS file format
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Introduction
Purpose and Development
The LAS (LASer) file format serves as an open binary interchange standard for exchanging 3-dimensional point cloud data, originally developed for airborne LiDAR acquisitions but also supporting terrestrial, bathymetric, and other sensor-derived datasets to facilitate interoperability among hardware vendors, software developers, and data users.[6] This format addresses the need for a vendor-neutral structure to store geospatial coordinates, intensity values, and associated metadata without proprietary constraints, enabling efficient data sharing in remote sensing applications.[7] Initiated by the American Society for Photogrammetry and Remote Sensing (ASPRS) Lidar Division's LAS Working Group in 2003, the format's first version, LAS 1.0, was released on May 9, 2003, establishing a foundational binary structure for point records and headers.[7][8] The specification evolved through iterative revisions to accommodate advancing LiDAR technologies: LAS 1.1, released on May 7, 2005, introduced GPS time stamps for precise temporal referencing of points.[9] LAS 1.2, released on April 29, 2008, added support for RGB color values to integrate photogrammetric enhancements.[3] LAS 1.3, approved in August 2009 with specification issued October 24, 2010, incorporated full waveform data packets and expanded classification options to 256 discrete classes for improved point categorization. LAS 1.4, approved in 2011 with its latest revision (R16) issued in August 2025, introduced 64-bit offset support for larger datasets, up to 15 returns per pulse, and Well-Known Text (WKT) coordinate reference system definitions.[10][11] The LAS format has achieved widespread adoption as the de facto standard for topographic and hydrographic point cloud data, mandated by the U.S. Geological Survey (USGS) in its 3D Elevation Program (3DEP) deliverables and by the National Oceanic and Atmospheric Administration (NOAA) for coastal and marine LiDAR projects.[12][13][14] It has also been endorsed internationally, including as an Open Geospatial Consortium (OGC) Community Standard in March 2018, promoting global consistency in geospatial data exchange.[15] LAS 1.5 was released in August 2025, incorporating features like point density validation methods (e.g., the Voronoi method) and support for synthetic aperture-derived points, following a public comment period from April to May 2025.[16][17]Key Features and Versions
The LAS file format is a binary standard designed for the efficient storage and interchange of large-scale 3D point cloud data, capable of handling up to billions of points through the use of 64-bit integer extents for coordinates and other spatial parameters in version 1.4 and later.[10] This binary structure, employing little-endian byte order, minimizes file sizes while preserving data integrity for lidar-derived and other point cloud datasets.[10] Core features of the format include scalable precision for point coordinates, achieved via offset and scale factors that allow representation of sub-millimeter accuracy within fixed-size integer fields, adapting to varying project requirements without altering the overall file schema.[10] It supports multiple returns per laser pulse, enabling up to 15 returns in version 1.4 to capture detailed vertical structures in vegetation or terrain.[10] Classifications are expanded to 256 distinct categories in 1.4, facilitating nuanced labeling of points such as ground, vegetation, or buildings.[10] Optional attributes enhance data richness, including intensity values for signal strength, scan angle for beam orientation, and GPS time for temporal synchronization.[10] The format maintains backward compatibility across versions from 1.5 down to 1.0, ensuring older software can read newer files by ignoring unrecognized elements.[10] Point data records are categorized into legacy formats 0 through 5, which use simple integer coordinates, and extended formats 6 through 10, which incorporate double-precision coordinates and require Well-Known Text (WKT) representations for Coordinate Reference Systems (CRS) to specify spatial projections.[10] Version 1.4 introduces several enhancements for advanced lidar applications, including an overlap flag to indicate points from overlapping flight lines, a scanner channel identifier for multi-channel systems, and a synthetic point flag that designates class 1 for algorithmically generated points rather than directly measured ones.[10] Additionally, extra bytes Variable Length Records (VLRs) allow for the inclusion of custom attributes, such as color or waveform data, extending the format's flexibility.[10] Structural limits in the format promote interoperability while constraining overhead: the public header block is fixed at 375 bytes, Variable Length Records (VLRs) are capped at 65,535 bytes each for metadata like georeferencing, and Extended VLRs (EVLRs) accommodate larger payloads, such as full waveforms exceeding 65 KB.[10] These constraints balance efficiency with the need to support expansive datasets in geospatial workflows.[10]File Organization
Version and Well Information Sections
LAS files are organized as plain-text ASCII files divided into sections, each starting with a tilde (~) prefix followed by a section name in uppercase (e.g., ~VERSION). Sections are mandatory or optional, appear in a prescribed order, and contain key-value pairs or data arrays delimited by spaces, commas, or tabs as specified in the ~Version section. The format supports backward compatibility across versions, with LAS 2.0 using fixed sections for one-dimensional log data and LAS 3.0 extending to multidimensional arrays and additional data types like core analyses.[18][19] The first mandatory section, ~Version, identifies the file's LAS version (e.g., "VERS. 2.0" or "VERS. 3.0 : CWLS LAS FORMAT VERSION 3.0"), wrap status ("WRAP. NO" for non-wrapped data, deprecated in 3.0), and data delimiter ("DLM. SPACE" or alternatives like comma or tab). It may include a program identifier for the creating software. This section ensures parsers recognize the file structure and data layout.[18] Immediately following is the mandatory ~Well section, which provides essential well identification and logging parameters. It includes mnemonics such as "WELL." for well name, "LOC." for location, "CTRY." for country, "SRVC." for service company, "DATE." for logging date (in DD-MMM-YYYY format), "UWI." for unique well identifier, "API." for API number, latitude ("LATI."), longitude ("LONG."), elevation ("ELEV."), and time zone ("TZ."). Depth-related fields cover start depth ("STRT."), stop depth ("STOP."), step interval ("STEP."), and null value indicator ("NULL."). In LAS 3.0, it requires at least 11 specific parameters for completeness. This section establishes the spatial and temporal context for the log data.[18][19]Curve and Parameter Sections
The mandatory ~Curves section (or ~Curve in some versions) lists the log traces included in the file, with one line of mnemonic-unit pairs corresponding to each column in the data array. For example: "~Curves DEPT.FT GR.GAPI NPHI.PU" defines depth (DEPT) in feet, gamma ray (GR) in API units, and neutron porosity (NPHI) in porosity units. Mnemonics are uppercase, up to 10 characters, followed by a period and 3-6 character units (e.g., FT, GAPI, PU). This section defines the structure of the subsequent data, ensuring interoperability. In LAS 3.0, for multidimensional data, this is replaced by a ~Definition section within data sets.[18] The optional ~Parameter section (or ~Params) stores supplementary one-dimensional well attributes as key-value pairs, such as "RUN. 1" for run number, "DREF. 500" for depth reference, "BHA. 7 1/2"" for bottom-hole assembly size, or fluid properties like mud weight ("MDWT. 9.2 PPG"). Each parameter has a mnemonic, unit, value, and description. Multiple ~Parameter sections can exist for different runs or tools. In LAS 3.0, these are grouped within data section sets for logs, cores, or other types. This enriches the dataset without altering the core log structure.[18][19] An optional ~Other section allows free-form comments or additional text, often used for tool calibration notes or disclaimers. It is less structured and deprecated in favor of more specific sections in LAS 3.0.[19]| Section | Mandatory/Optional | Key Contents | Version Notes |
|---|---|---|---|
| ~Version | Mandatory | Version (e.g., 2.0, 3.0), wrap (NO), delimiter (SPACE) | 3.0 adds program ID |
| ~Well | Mandatory | Well name, location (LATI, LONG), depths (STRT, STOP, STEP), NULL value | Requires 11 params in 3.0 |
| ~Curves | Mandatory (2.0) | Mnemonic-unit pairs for log traces (e.g., DEPT.FT) | ~Definition in 3.0 for arrays |
| ~Parameter | Optional | Key-value metadata (e.g., MDWT. 9.2 PPG) | Grouped in data sets in 3.0 |
| ~Other | Optional | Free-form comments | Deprecated in 3.0 |
Data Section
The mandatory data section, ~ASCII in LAS 2.0 or ~Data in LAS 3.0, contains the numerical log values as a delimited array, with one row per depth step. Each row starts with the index value (typically depth, e.g., "3264.500 DEPT GR NPHI"), followed by values for each curve, using the null indicator (-999.25 or specified) for missing data. Data supports floating-point (default), integer, string, exponential, date-time, and degree-minute-second formats, with precision controlled by {F x.y} or similar descriptors in 3.0.[18] In LAS 3.0, the data section is part of extensible "data section sets" for multiple runs or types (e.g., ~Log_Data, ~Core_Data), supporting 1D curves, 2D arrays (e.g., for image logs), and 3D arrays (e.g., for dipole sonic). Sections are indexed (e.g., ~Log_Data[20]) for multiple instances, with preceding ~Parameter and ~Definition sections. This allows comprehensive storage of geophysical, geological, and petrophysical data while maintaining the simple ASCII parsing. Files end without a specific terminator, relying on the ~ASCII or ~Data marker to signal the start.[18][19]Point Data Records
Legacy Formats
The legacy point data record formats 0 through 5 in the LAS specification form the foundational structures for encoding LiDAR point cloud data, originating from the earliest versions of the standard and continuing to support backward compatibility in later releases. These formats prioritize efficiency for basic airborne and terrestrial LiDAR datasets, accommodating essential geometric, radiometric, and metadata attributes while maintaining compact record sizes ranging from 20 to 63 bytes per point. They are particularly prevalent in datasets generated by pre-2011 systems, where advanced features like multi-return expansion or high-precision waveform descriptors were not yet standardized. Limitations include support for up to five returns per emitted pulse, 32 classification categories (values 0-31), and scan angle ranks encoded in a single signed byte representing -90 to +90 degrees in 0.006-degree increments.[6][11] Format 0, the simplest legacy variant at 20 bytes per point, includes core spatial coordinates as scaled long integers (X, Y, Z; 4 bytes each), intensity as an unsigned short (2 bytes, ranging 0-65535), a flags byte (1 byte) detailing return number (bits 0-2: 1-5), number of returns (bits 3-5: 1-5), scan direction (bit 6: 0 right-to-left, 1 left-to-right), and edge of flight line (bit 7: 0 interior, 1 edge), classification as an unsigned char (1 byte), scan angle rank as a signed char (1 byte), user data as an unsigned char (1 byte), and point source ID as an unsigned short (2 bytes, identifying the originating flight line or scanner). This format suits unenhanced LiDAR surveys focused on elevation modeling without temporal or colorimetric data.[6] Format 1 extends Format 0 to 28 bytes by appending GPS time as a double-precision float (8 bytes, in seconds since the GPS epoch of January 6, 1970, 00:00:00 UTC), enabling temporal synchronization for trajectory-aware processing in multi-pulse scans. It remains ideal for legacy datasets requiring pulse timing without color or waveform details.[6] Format 2, at 26 bytes, builds on Format 0 by adding RGB color values (red, green, blue; each an unsigned short of 2 bytes, ranging 0-65535), facilitating visualization integration with imagery from co-registered cameras in early hyperspectral or photogrammetric LiDAR workflows.[6] Format 3 combines the enhancements of Formats 1 and 2 into a 34-byte record, incorporating both GPS time (8 bytes) and RGB colors (6 bytes total) for temporally and visually enriched point clouds, commonly used in pre-2011 urban mapping projects blending LiDAR with aerial photography.[6] Format 4, expanded to 57 bytes, incorporates waveform packet data atop Format 1's structure: wave packet descriptor index (unsigned char, 1 byte, referencing up to 256 descriptors in the file header), byte offset to waveform data packet (unsigned long long, 8 bytes, file-relative position), waveform packet size (unsigned long, 4 bytes), and return point waveform location (float, 4 bytes) with parametric offsets dx, dy, dz (each float, 4 bytes, relative to the point in meters). This format supports full-waveform decomposition for vegetation penetration analysis in legacy full-waveform LiDAR systems, with coordinate reference system details handled via GeoTIFF variable-length records for backward compatibility.[6][11] Format 5, the most feature-complete legacy option at 63 bytes, merges Format 3's GPS time and RGB with Format 4's waveform attributes, serving complex datasets from early hybrid sensors combining discrete returns, colors, timing, and pulse shapes, such as in environmental monitoring applications prior to the 2011 specification update.[6]| Format | Size (bytes) | Key Additions Over Format 0 | Primary Use Case |
|---|---|---|---|
| 0 | 20 | None (core fields only) | Basic elevation data |
| 1 | 28 | GPS time (8) | Time-synchronized scans |
| 2 | 26 | RGB colors (6) | Colorized point clouds |
| 3 | 34 | GPS time (8) + RGB (6) | Visual-temporal mapping |
| 4 | 57 | Waveform descriptors (29) | Full-waveform analysis |
| 5 | 63 | GPS time (8) + RGB (6) + waveform (29) | Hybrid sensor data |
Extended Formats
The extended point data record formats 6 through 10, introduced in LAS version 1.4, expand upon the capabilities of earlier formats by incorporating higher precision for coordinates (scaled integers with 32 bits each for X, Y, Z), mandatory GPS time stamping, and additional flags for data quality and processing attributes.[6] These formats support up to 15 returns per pulse (encoded in 4 bits) and 256 classification values (using 1 byte), compared to the limitations in legacy formats 0-5.[6] They also include enhanced bit fields in the return information and classification bytes to flag synthetic points, keypoints, withheld points, and overlaps, enabling more nuanced lidar data management.[6] The return information byte (2 bytes total) allocates bits 0-3 for the return number (1-15) and bits 4-7 for the number of returns (1-15), providing finer granularity for multi-return pulses.[6] The classification byte (1 byte) uses 5 bits (0-4) for the classification value (0-31, extensible to 256 with higher bits) and includes 4 flag bits: bit 5 for synthetic points (indicating non-directly measured points, often from interpolation), bit 6 for keypoints (critical features), bit 7 for withheld points (excluded from processing), and an additional overlap flag (bit 5 in some contexts, but primarily bit 7 in extended use for overlap detection).[6] A deleted flag is integrated into bit 6 of the classification byte across these formats, allowing points to be marked for removal without altering the file structure.[6] The scanner channel is encoded in 2 bits (0-3, for multi-channel systems), and the scan angle uses 2 bytes for values from -360 to +360 degrees in 0.006-degree increments.[6] Synthetic points are further supported via the synthetic flag in classification and source ID flags in the point source ID field (2 bytes, values 1-65535 indicating origin).[6] Format 6 serves as the 30-byte base for these extensions, including the enhanced flags, GPS time (8 bytes, double-precision), and point source ID (2 bytes), but without color or waveform data.[6] Format 7 extends this to 36 bytes by adding RGB color values (3 unsigned shorts, 16 bits each, scaled 0-65535).[6] Format 8 increases to 38 bytes, incorporating near-infrared (NIR) data (2 bytes, unsigned short) alongside the RGB from format 7 for multispectral applications.[6] Formats 9 and 10 build on waveform-enabled structures similar to legacy formats 4 and 5 but with the new flags and precision. Format 9 (59 bytes) adds full waveform packet data, including descriptor index (1 byte), byte offset to waveform (8 bytes), waveform packet size (4 bytes), return point location (4 bytes), and parametric offsets dx/dy/dz (3 x 4 bytes).[6] Format 10 (67 bytes) combines this waveform support with RGB and NIR colors from formats 7 and 8.[6] All extended formats require GPS time as a mandatory field for temporal synchronization and Well-Known Text (WKT) Coordinate Reference System (CRS) representation in the file header, replacing GeoTIFF for these point types to ensure precise georeferencing.[6]| Format | Bytes | Key Additions Over Base |
|---|---|---|
| 6 | 30 | Enhanced flags, GPS time, scan angle (2 bytes), scanner channel |
| 7 | 36 | RGB (3 × 2 bytes) |
| 8 | 38 | RGB + NIR (2 bytes) |
| 9 | 59 | Waveform packet data (29 bytes total) |
| 10 | 67 | Waveform + RGB + NIR |
Data Attributes
Well Information and Location
The ~WELL section in the LAS file format provides essential identification and location attributes for the well, serving as a mandatory component to contextualize the log data. Key mnemonics include WELL (well name, up to 40 characters), FLD (field name), LOC (location identifier), CTRY (country code), STAT (state or province), DATE (logging date in DD-MMM-YYYY format), SRVC (service company name), COMP (company name), and LIC (license number).[19] Location attributes encompass coordinate data, such as LATI (latitude in decimal degrees, positive north), LONG (longitude in decimal degrees, positive east), X and Y coordinates if applicable, and GDAT (geodetic datum, e.g., "WGS84"). Elevation details include KB (kelly bushing elevation in specified units, e.g., FT or M), RT (rotary table elevation), and GL (ground level elevation). The section also defines the log index range with STRT (start depth), STOP (stop depth), STEP (step interval), all in consistent units (e.g., M or FT), and NULL (null value indicator, e.g., -999.25). These attributes ensure traceability and georeferencing of the borehole data, with units and descriptions provided for each mnemonic to promote standardization.[18]Parameters
The optional ~PARAMETER (or ~Params in LAS 3.0) section stores supplementary one-dimensional attributes related to the well, tools, or environmental conditions, enhancing the dataset with metadata not covered in ~WELL. Each parameter is recorded as a four-field line: mnemonic (up to 10 characters, e.g., BHT for bottom-hole temperature), value (numeric or string, e.g., 120.5), unit (up to 6 characters, e.g., DEG C), and description (free-text explanation, e.g., "Bottom Hole Temperature"). Common examples include tool-specific details like LITH (lithology description), BS (bit size in IN), or MD (measured depth at a reference).[21] In LAS 3.0, parameters can be grouped under specialized sections such as ~Core (for core analysis attributes like porosity, permeability) or ~Inclinometry (for deviation survey data like AZIM for azimuth, MD for measured depth). Values support various formats (integer, floating-point, date), with nulls handled via the global NULL value. This section facilitates petrophysical interpretation by providing context for log corrections and quality control, maintaining backward compatibility with LAS 2.0.[18]Curve Data
The mandatory ~CURVE section (or ~Curves/~Log_Definition in LAS 3.0) defines the attributes of the log traces, listing each curve's mnemonic, units, API code (if applicable), and description to enable accurate data interpretation. The first mnemonic is typically the index, such as DEPT (depth in FT or M) or TIME (time in S for time-based logs). Subsequent mnemonics represent measurements, e.g., GR (gamma ray in API units), NPHI (neutron porosity in V/V or PU), or LLSD (laterolog deep resistivity in OHMM). Each line follows the format: mnemonic (up to 10 characters), unit (up to 6 characters, e.g., API, OHMM, US/G), API (industry code or blank), description (text, e.g., "Gamma Ray"). In LAS 3.0, extended support for arrays (e.g., NMR[1:10] for multi-channel data) and frames allows multidimensional attributes, with formats specified (e.g., {F6.2} for floating-point). These attributes directly precede the ~ASCII section, where numerical values are arrayed row-wise, delimited by spaces or commas, ensuring interoperability in analysis software. Units must be consistent across the file, and descriptions aid in identifying curve purposes, such as distinguishing corrected vs. raw data.[19][18]Georeferencing
Coordinate Systems
The LAS file format for well logging provides georeferencing primarily through the mandatory ~WELL section, which stores well location and elevation data using simple mnemonic-based parameters. This section supports geographic coordinates via latitude and longitude, or projected coordinates using X and Y values, along with associated datum information. Unlike multidimensional point cloud formats, well log LAS files focus on one-dimensional depth-indexed data tied to the well's surface location.[18] Key mnemonics for horizontal positioning include:- LATI: Latitude of the well location, in decimal degrees or degrees/minutes/seconds (e.g., 45.37° 12' 58" N).
- LONG: Longitude of the well location, in decimal degrees or degrees/minutes/seconds (e.g., 13.22° 30' 09" W).
- X and Y: Easting and northing coordinates for projected systems, in meters or feet, as alternatives to LATI/LONG.
- KB or RKB: Elevation of the rotary kelly bushing, the common depth reference point.
- GL: Ground level elevation at the well site.
- EREF: Elevation of the depth reference point, in the units specified (default meters).
Projection and Metadata
Projection details in LAS well log files are limited to the specification of the horizontal coordinate system in the ~WELL section via HZCS, which identifies the map projection (e.g., "Lambert Conformal Conic" or UTM parameters). No dedicated records for transformation parameters like scale factors or false origin are included; users rely on external definitions from the datum and projection codes. For UTM, the zone and hemisphere are typically appended (e.g., "UTM 15N").[18] Additional metadata enriches georeferencing context:- COUN: Country code, using ISO standards for jurisdictional reference.
- SRVC: Service company, often providing the location survey.
- Comments in the ~WELL section can include survey details, such as GPS accuracy or datum transformation notes.
Derivatives
LAZ Compression
The LAZ format is a lossless compression extension for the LAS file format, designed to significantly reduce file sizes while preserving all original data for exact reconstruction. Developed by Martin Isenburg and presented in November 2011 at the European LiDAR Mapping Forum in Salzburg, it builds directly on the LAS 1.4 specification and is implemented through the open-source LASzip library.[22][23] LAZ employs entropy coding combined with predictive arithmetic techniques to exploit redundancies in LiDAR point data, such as spatial correlations and repeating attribute values, enabling efficient compression without any loss of information.[24][25] LAZ files maintain binary compatibility with LAS files upon decompression, differing only in the compressed point data records section, which is organized into fixed-size chunks (default 50,000 points) for streaming and random access support. The file header includes a mandatory "laszip encoded" Variable Length Record (VLR) with Record ID 22204, which specifies the compressor version, chunk size, and a list of compressed items tailored to the point format. These items define reversible coders for individual fields: for example, X, Y, and Z coordinates use differential encoding with second-order prediction (medians of prior differences for X/Y and previous return for Z); intensity values are encoded via differences from the most recent value using context-based arithmetic coding (four contexts based on return number); and classification bytes employ 256-context entropy coding to handle the limited range of values efficiently. LAZ supports all LAS point data record formats 0 through 10, with formats 0-5 using pointwise compression and formats 6-10 employing layered chunked compression for extended attributes like color or waveform data.[24][23] LAZ achieves typical size reductions to 7-20% of the original LAS file (equivalent to 5-14x compression). This results in substantial savings for large datasets; for instance, a 776 GB LAS file containing 30 billion points can be compressed to 64 GB in LAZ format. The process is fully reversible, ensuring decompressed output is bit-identical to the source LAS file, which has made LAZ the de facto industry standard for LiDAR data storage and distribution.[24][23][22] Encoding and decoding are facilitated by the LAStools suite, which includes the laszip command-line utility for direct conversion between LAS and LAZ files, and the LASzip library is integrated into broader ecosystems such as PDAL for point cloud processing pipelines and CloudCompare for visualization and analysis.[22]COPC Format
The Cloud Optimized Point Cloud (COPC) format is an extension of the LAZ 1.4 compressed LAS format that incorporates a clustered octree structure for efficient spatial indexing and querying of point cloud data. Developed by Howard Butler, Andrew Bell, and Connor Manning at Hobu, Inc., and released in 2021, COPC enables partial and hierarchical access to large datasets without requiring the entire file to be loaded into memory, making it suitable for cloud-based and web delivery applications.[26][27] COPC files maintain the core LAZ structure but add specific Variable Length Records (VLRs) to define the octree organization. The primary info VLR (User ID: "copc", Record ID: 1) is a 160-byte record located at offset 375 in the file header, containing the unscaled octree center coordinates (center_x, center_y, center_z as doubles), the root node halfsize (double, representing the distance from center to edge along each axis), base spacing (double, which halves at each subsequent level), offset and size of the root hierarchy page (uint64_t each), and the minimum/maximum GPSTime values (doubles), followed by 11 reserved uint64_t fields set to zero. This VLR effectively defines the overall bounding box using six double-precision values derived from the center and halfsize. The hierarchy VLR (User ID: "copc", Record ID: 1000) stores the octree metadata in one or more fixed-size pages, each comprising consecutive 32-byte entries for octree nodes; each entry includes a VoxelKey (level as int32_t, followed by x, y, z coordinates as int32_t, with negative values indicating invalid nodes) and an Entry struct (offset as uint64_t, byte size as int32_t, point count as int32_t: positive for leaf nodes with points, -1 for internal nodes linking to child pages, or 0 for empty nodes). COPC requires LAZ 1.4 with Point Data Record Formats (PDRF) 6, 7, or 8 to support the necessary extended header fields.[27] The indexing mechanism in COPC relies on an octree hierarchy starting at level 0 (root) and descending to a maximum level determined by the data density and spacing, where each level subdivides the space into eight child nodes with halved spacing. Hierarchy pages group entries for nodes whose bounding volumes contain points, allowing readers to traverse from the root page (whose offset and size are specified in the info VLR) to subpages or data chunks via the entry offsets and sizes; leaf nodes point directly to compressed LAZ chunks of points within their bounds. This structure supports spatial filtering by bounds or density, as applications can skip irrelevant branches and stream only required pages or chunks over networks, reducing I/O overhead for massive datasets.[27] In practice, COPC facilitates web and cloud delivery of point clouds, with tools like PDAL for reading/writing and Potree 2.0 for visualization providing native support; it is particularly effective for national-scale LiDAR repositories, such as the USGS 3D Elevation Program (3DEP), where it minimizes data transfer for subset queries compared to unindexed LAZ files.[28][29][30]References
- Sep 1, 1989 · The Canadian Well Logging Society's Floppy Disk Committee has designed a standard format for log data on floppy disks. It is known as the LAS ...