• LIDAR Data：

LIDAR數據類似于帶有激光的RADAR，是光檢測和測距的縮寫。
laspy庫提供了python API，用于讀取，寫入和操作一種流行的用來存儲LIDAR數據的（.LAS文件）。 LAS文件是根據幾種規格打包的二進制文件。

• Las： 二進制格式；是點云lidar數據的一種典型格式。
  las文件是根據多種las規格打包而成的二進制文件。
• Las 規格
  las1.0支持las1.0~1.2，對格式1.3，1.4提供了初步支持。

las規格	文檔
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

• 頭文件

las1.0~las1.2	las1.3~las1.4
頭文件區	頭文件區
變長記錄區	變長記錄區
點數據區	點數據區
	波形數據記錄區、擴展變長記錄區

藍色：las1.3新增頭文件區
紅色：las1.4新增頭文件區

屬性名	laspy縮寫	文件格式（長度）
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)

• 點格式：

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規格	支持的點數據格式
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減少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

點格式：

Field Name	laspy簡寫	File Format[number] (length)	備注
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

總結

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