LAS ProjectID Encoding and Representation

LAS GUIDs as encoded in the four ProjectID fields of the LAS header are intended to follow Microsoft-style 4-2-2-2-6 UUIDs with one 4-byte unsigned integer, followed by three 2-byte unsigned integers, followed by one 6-byte unsigned integer. The first three integers are customarily encoded in Little-Endian (LE) format, while the last two integers are encoded in Big-Endian (BE) format as follows:

4u-2u-2u-2u-6u
LE-LE-LE-BE-BE

Since the LAS file uses Little-Endian encoding, the final two integers are encoded in LAS as an 8-byte unsigned char array to maintain byte order.

LAS data types:   U32 - U16 - U16 - CC - CCCCCC
LAS Project ID: | p1  | p2  | p3  |     p4     |

GUID/UUID Representations

It is customary to represent GUIDs as a string in hexadecimal format, with two characters for each byte. The following presents several representations of the same GUID using different interpretations of the LAS Project ID raw data:

Standard Hex GUID String:      00112233-4455-6677-8899-AABBCCDDEEFF
LAS Project ID (raw bytes):    [33 22 11 00][55 44][77 66][88 99 AA BB CC DD EE FF]         <-- note BE order of the last section
LAS Project ID (integers):     [1122867    ][17493][26231][136 153 170 187 204 221 238 255] <-- note LE interpretation of first 3 sections
LAS Project ID (raw bits):     [00110011 00100010 00010001 00000000]
                               [01010101 01000100]
                               [01110111 01100110]
                               [10001000 10011001 10101010 10111011 11001100 11011101 11101110 11111111]

Download samples:

• Raw: Example
• LAS: Example

ProjectID4 as a String?

Because the fourth ProjectID field is an unsigned char array, some users have elected to manipulate the GUID such that it spells out a word relevant to the project when the unsigned char values are interpreted literally against the standard ASCII table. For example:

Standard Hex GUID String:      00112233-4455 -6677 -4D79-50726F6A3031
LAS Project ID (raw bytes):    33221100-5544 -7766 -4D79-50726F6A3031
LAS Project ID (literal):      1122867 -17493-26231-M y  P r o j 0 1 <-- literally, "MyProj01"
                                U32    - U16 - U16 -  C x8

Note that ASCII values 128 and above, which usually comprise accented letters (e.g., "ü"), do not have a globally standard representation and will vary widely based on your region.

Download samples:

• Raw: Example
• LAS: Example

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Following these recommendations is not required for a compliant LAS file because Project ID values are primarily for your own internal use. Hopefully, though, this gives you some ideas for your own implementations.

Read more here:

• Microsoft blog: https://blogs.msdn.microsoft.com/openspecification/2013/10/08/guids-and-endianness-endi-an-ne-ssinguid-or-idne-na-en-ssinguid/
• Wikipedia: https://en.wikipedia.org/wiki/Universally_unique_identifier#Encoding