Specification > Header

Header Structure

Bytes
0   2                       14                                      34             42               50              58
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.....
| V |          TYPE         |              DEVICE_NAME              |   TIME_STAMP  |   BODY_SIZE   |     CRC64     |   BODY  		  
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.....

Byte Order

Big endian should be used for all numerical values (version, body size, crc). Unused spaces are padded with 0 (binary).

Header Fields

Data	Type	Description
V	Unsigned short (16bit)	Version number (1)
TYPE	char[12]	Type name of data
DEVICE_NAME	char[20]	Unique device name
TIME_STAMP	64 bit unsigned int	Timestamp or 0 if unused
BODY_SIZE	64 bit unsigned int	Size of body in bytes
CRC	64 bit unsigned int	64 bit CRC for body data

Description of Fields

Version number

The version number field specifies the header format version. Currently the version number is 1. Please note that this is different from the protocol version.

Type name

The type name field is an ASCII character string specifying the type of the data contained in the message body e.g. “TRANSFORM”. The length of the type name must be within 12 characters.

Device name

The device name field contains an ASCII character string specifying the name of the the message.

Timestamp

The timestamp field contains a 64-bit timestamp indicating when the data is generated. Please refer Timestamp for the format of the 64-bit timestamp.

Body size

CRC

The 64-bit CRC used in OpenIGTLink protocol is based on ECMA-182 standard. An example code is available in igtl_util.c in the OpenIGTLink library.