las点云数据格式

• LIDAR Data：

LIDAR数据类似于带有激光的RADAR，是光检测和测距的缩写。
laspy库提供了python API，用于读取，写入和操作一种流行的用来存储LIDAR数据的（.LAS文件）。 LAS文件是根据几种规格打包的二进制文件。

• Las： 二进制格式；是点云lidar数据的一种典型格式。
  las文件是根据多种las规格打包而成的二进制文件。
• Las 规格
  las1.0支持las1.0~1.2，对格式1.3，1.4提供了初步支持。

las规格	文档
1.0	http://www.asprs.org/a/society/committees/standards/asprs_las_format_v10.pdf
1.1	http://www.asprs.org/a/society/committees/standards/asprs_las_format_v11.pdf
1.2	http://www.asprs.org/a/society/committees/standards/asprs_las_format_v12.pdf
1.3	http://www.asprs.org/a/society/committees/standards/LAS_1_3_r11.pdf
1.4	http://www.asprs.org/a/society/committees/standards/LAS_1_4_r11.pdf

• 头文件

las1.0~las1.2	las1.3~las1.4
头文件区	头文件区
变长记录区	变长记录区
点数据区	点数据区
	波形数据记录区、扩展变长记录区

蓝色：las1.3新增头文件区
红色：las1.4新增头文件区

属性名	laspy缩写	文件格式（长度）
File Signature	file_signature	char[4] (4)
File Source Id	file_source_id	unsigned short[1] (2)
(Reserved or Global Encoding)	global_encoding	unsigned short[1] (2)
Gps Time Type	gps_time_type	Part of Global Encoding
Project Id (4 combined fields)	guid	ulong+ushort+ushort+char[8] (16)
Verion Major	version_major	unsigned char[1] (1)
Version Minor	version_minor	unsigned char[1] (1)
Version Major + Minor	version	(see above)
System Identifier	system_id	char[32] (32)
Generating Software	software_id	char[32] (32)
File Creation Day of Year	(handled internally)	unsigned short[1] (2)
File Creation Year	(handled internally)	unsigned short[1] (2)
Creation Day + Year	date	(see above)
Header Size	header_size	unsigned short[1] (2)
Offset to Point Data	data_offset	unsigned long[1] 4
Number of Variable Length Recs	(handled internally)	unsigned long[1] 4
Point Data Format Id	data_format_id	unsigned char[1] (1)
Data Record Length	data_record_length	unsigned short[1] (2)
Number of point records	records_count	unsigned long[1] (4)
Number of Points by Return Ct.	point_return_count	unsigned long[5 or 7] (20 or 28)
Scale Factor (X, Y, Z)	scale	double[3] (24)
Offset (X, Y, Z)	offset	double[3] (24)
Max (X, Y, Z)	max	double[3] (24)
Min (X, Y, Z)	min	double[3] (24)
Start of waveform data record	start_waveform_data_rec	unsigned long long[1] (8)
Start of first EVLR	start_first_evlr	unsigned long long[1] (8)
Number of EVLRs	(handled internally)	unsigned long[1] (4)
Number of point records	point_records_count	unsigned long long[1] (8)
Number of points by return ct.	point_return_count	unsigned long long[15] (120)

• 点格式：

LAS Format	Point Formats Supported
1.0，1.1	0, 1
1.2	0, 1, 2, 3
1.3	0, 1, 2, 3, 4, 5
1.4	0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

LAS规格	支持的点数据格式
1.0，1.1	0,1（x、y、z、intensity、flag_type、raw_classification、user_data、pt_src_id，1新增gps_time）
1.2	0, 1, 2, 3（2减少gpsTime，3新增red、green、blue）
1.3	0, 1, 2, 3, 4, 5，新增wavefm_packet_desc_index、byte_offset_to_waveform_data等；
1.4	0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

点格式：

Field Name	laspy简写	File Format[number] (length)	备注
X	X (x for scaled)	long[1] (4)
Y	Y (y for scaled)	long[1] (4)
Z	Z (z for scaled)	long[1] (4)
Intensity	intensity	unsigned short[1] (2)
(Flag Byte)	flag_byte	unsigned byte[1] (1)
(Classification Byte)	raw_classification	unsigned byte[1] (1)
User Data	user_data	unsigned char[1] (1)
Point Source Id	pt_src_id	unsigned short[1] (2)
GPS Time	gps_time	double[1] (8)	1新增
Red	red	unsigned short[1] (2)	2新增
Green	green	unsigned short[1] (2)	2 新增
Blue	blue	unsigned short[1] (2)	2 新增