LAS file format: public header block

LAS is published by the American Society for Photogrammetry and Remote Sensing (ASPRS). This reference follows LAS 1.4 revision 15 and LAS 1.5 revision 0, approved in August 2025, and notes where earlier versions differ. All numbers are little-endian. Text fields are ASCII, padded with zero bytes. Fields that are not required and not used must be zero.

Versions

Version	Header size	Point formats	Main changes
1.0	227	0, 1	Bytes 4 to 7 reserved
1.1	227	0, 1	File Source ID at byte 4
1.2	227	0 to 3	Global Encoding at byte 6 (GPS time type); colour formats
1.3	235	0 to 5	Waveform data and its offset in the header
1.4	375	0 to 10	64-bit point counts, 15 returns, 256 classes, extended VLRs, WKT
1.5	393	6 to 10	GPS time range and Time Offset; formats 0 to 5 and GeoTIFF systems dropped

A reader should take the header’s length from Header Size rather than from the version, and must use Offset to Point Data to find the points.

Header fields

Offset	Size	Type	Name	Versions	Meaning
0	4	char[4]	File Signature	All	`LASF`
4	2	uint16	File Source ID	1.1 on	Source of the file, such as a flight line, 1 to 65,535; 0 means none assigned, as for a merged tile
6	2	uint16	Global Encoding	1.2 on	Bit field; see below. Reserved (0) in 1.1
8	4	uint32	Project ID – GUID data 1	All	Optional project identifier, together with the next three fields
12	2	uint16	Project ID – GUID data 2	All
14	2	uint16	Project ID – GUID data 3	All
16	8	uint8[8]	Project ID – GUID data 4	All
24	1	uint8	Version Major	All	1
25	1	uint8	Version Minor	All	0 to 5
26	32	char[32]	System Identifier	All	Hardware, or the operation that made the file; see below
58	32	char[32]	Generating Software	All	Software and version, such as `TerraScan V-10.8`
90	2	uint16	File Creation Day of Year	All	Day of the year in GMT, 1 January being day 1
92	2	uint16	File Creation Year	All	Four-digit year
94	2	uint16	Header Size	All	Size of this header in bytes
96	4	uint32	Offset to Point Data	All	Bytes from the start of the file to the first point
100	4	uint32	Number of Variable Length Records	All	VLRs between the header and the points
104	1	uint8	Point Data Record Format	All	0 to 10; see point records
105	2	uint16	Point Data Record Length	All	Bytes per point; anything beyond the format’s own fields is extra bytes
107	4	uint32	Legacy Number of Point Records	All	Number of points (the only count before 1.4). From 1.4, 0 unless the file keeps legacy compatibility
111	20	uint32[5]	Legacy Number of Points by Return	All	Points that are return 1 to 5, under the same rule
131	8	float64	X Scale Factor	All	Multiplier for stored X, such as 0.01
139	8	float64	Y Scale Factor	All
147	8	float64	Z Scale Factor	All
155	8	float64	X Offset	All	Added after scaling
163	8	float64	Y Offset	All
171	8	float64	Z Offset	All
179	8	float64	Max X	All	Actual extents of the points, as real coordinates; 0 if there are no points
187	8	float64	Min X	All
195	8	float64	Max Y	All
203	8	float64	Min Y	All
211	8	float64	Max Z	All
219	8	float64	Min Z	All
227	8	uint64	Start of Waveform Data Packet Record	1.3 on	Offset of waveform data inside the file; 0 if none or stored externally
235	8	uint64	Start of First Extended Variable Length Record	1.4 on	Offset of the first EVLR, or 0
243	4	uint32	Number of Extended Variable Length Records	1.4 on	EVLRs after the points
247	8	uint64	Number of Point Records	1.4 on	Number of points, always filled in
255	120	uint64[15]	Number of Points by Return	1.4 on	Points that are return 1 to 15
375	8	float64	Max GPS Time	1.5	Highest non-zero GPS time of the points, in the file’s time encoding
383	8	float64	Min GPS Time	1.5	Lowest non-zero GPS time
391	2	uint16	Time Offset	1.5	Used with Global Encoding bit 6; see below

A coordinate is stored value × scale factor + offset. For example, with X scale 0.01 and X offset 500000, a stored X of 1234567 is 512345.67.

From 1.4, a writer that keeps legacy compatibility fills both the legacy 32-bit counts and the new 64-bit ones; this is possible only with point formats 0 to 5 and at most 4,294,967,295 points. Otherwise the legacy fields are 0. If a non-zero legacy field disagrees with the new one, the specification tells readers to use the legacy value.

Global Encoding

Bit	Name	Meaning
0	GPS Time Type	0: GPS times in the points are GPS week time (seconds into the week). 1: Adjusted Standard GPS Time, standard GPS time minus 1,000,000,000 seconds. From 1.2
1	Waveform Data Packets Internal	Waveform data is inside this file (in 1.4 and 1.5 as an EVLR). Deprecated. From 1.3
2	Waveform Data Packets External	Waveform data is in a separate file with the same name and the extension `.wdp`. Never set together with bit 1. From 1.3
3	Synthetic Return Numbers	The return numbers were generated, for example by merging a first-return file and a last-return file. From 1.3
4	WKT	The coordinate system is given as OGC WKT rather than GeoTIFF keys. Required for point formats 6 to 10, and always set in 1.5. From 1.4
5	Reserved	0
6	Time Offset Flag	With bit 0 also set, GPS times are Offset GPS Time: standard GPS time minus 1,000,000 × Time Offset seconds. Must not be set without bit 0. From 1.5
7 to 15	Reserved	0

Standard GPS time counts seconds from midnight at the start of 6 January 1980. A Time Offset of 1000 gives the same result as Adjusted Standard GPS Time.

System Identifier

Made by	System Identifier
A hardware system	The hardware’s name, such as `ALS50`
Merging one or more files	`MERGE`
Modifying a single file	`MODIFICATION`
Extracting from one or more files	`EXTRACTION`
Reprojecting, rescaling, warping and so on	`TRANSFORMATION`
Another operation	`OTHER`, or up to 32 characters naming it

.LAS File Format – Public header block

Versions

Header fields

Global Encoding

System Identifier