OpenIGTLink/Protocol
Contents
Overview
Every message transfered from a sender to a receiver through OpenIGTLink communication consists of the header byte array followed by the body.
The header contains type string and size of the body, which helps receiver to interpret the body.
The type string may be one of the names defined in OpenIGTLink protocol specification (this page) or a name defined by a user.
The sender does not need to care whether the receiver can interpret the data type, since the receiver can skip reading the body as long as the body size information in the header is correct.
The header also contains device name. This would be helpful when the sender sends same type of data acquired from multiple sources. For example, if the sender has multi-channel tracking device, sender can assign different name to each channel, then the receiver can recognize from which channel data has been acquired.
Details of the header and body structures are defined in following sections.
Client - Server
A device (scanner, tracker) exposing functionality and executing commands is usually the Server. Once started will stand by listening for connection requests.
A Client (for ex. a PC) usually connects to multiple devices and coordinates the whole process.
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 |
Data types
Data type:
- Command (get position, get status, go to target, stop, start continuous push, stop push, ready)
- Data (image, position, status)
IMAGE
Bytes 58 60 62 64 70 82 94 106 118 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | V |T|S|E|O|RI |RJ |RK | TX | TY | TZ | SX | SY | SZ | NX | NY | NZ | PX | PY | PZ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 118 124 130 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.... |DI |DJ |DK |DRI|DRJ|DRK| IMAGE_DATA +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+....
Descriptions:
| Data | Type | Description |
| V | unsigned short | version number |
| T | 8bit unsigned int | Image type (1: Scalar) |
| S | 8bit unsigned int | Scalar type (2:int8 3:int8 4:int16 5:uint16 6:int32 7:uint32 10:float32 11:float64) |
| E | 8bit unsigned int | Endian for image data (1:BIG 2:LITTLE) (NOTE: values in image header is fixed to BIG endian) |
| O | 8bit unsigned int | image coordinate (1:RAS 2:LPS) |
| RI, RJ, RK | 16 bit unsigned int | Number of pixels in each direction |
| PX, PY, PZ | 32 bit float | center position of the image |
| TX, TY, TZ | 32 bit float | Transverse vector (direction for 'i' index) / The length represents pixel size in 'i' direction |
| SX, SY, SZ | 32 bit float | Transverse vector (direction for 'j' index) / The length represents pixel size in 'j' direction |
| NX, NY, NZ | 32 bit float | Normal vector of image plane(direction for 'k' index) / The length represents pixel size in 'z' direction or slice thickness |
| DI, DJ, DK | 16 bit unsigned int | Starting index of subvolume |
| DRI, DRJ, DRK | 16 bit unsigned int | number of pixels of subvolume |
| IMAGE_DATA | Binary image data () | Image data (endian is determined by "E" field) |
TRANSFORM
The transform data is upper three rows of 4x4 transformation matrix, where element (3,3) is assumed to be 1.
Each element is a 4 byte (32 bit) float, 12x4 = 48 byte in total.
Bytes (Body) 58 62 66 70 74 78 82 86 90 94 98 102 106 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | (0,0) | (1,0) | (2,0) | (0,1) | (1,1) | (2,1) | (0,2) | (1,2) | (2,2) | (0,3) | (1,3) | (2,3) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
POSITION
Parameters (24 byte total):
- Vector of three 32 bit (3x4 byte) floats: position X, Y, Z
- Vector of three 32 bit (3x4 byte) floats: orientation
The orientation is optional, if not used the values are (1,0,0)
Bytes (Body) 58 62 66 70 74 78 82 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | x | y | z | ox | oy | oz | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
GET_STATUS
Parameters: none (BODY_SIZE=0)
Response: one STATUS packet for each implemented device
STATUS
Bytes (Body) 58 60 68 88 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+..... | C | Sub Code | Status name | Status message (optional) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+.....
| Data | Type | Description |
| C | Unsigned short (16bit) | Status code groups: 1-Ok, 2-Generic Error, ... (see below) |
| Sub Code | 64 bit integer | Sub code for the error (ex. 0x200 - file not found) |
| Error name | char[20] | "Error", "Ok", "Starting up" - can be anything, don't relay on this |
| Status Message (optional) | char[ BodySize - 30 ] | Optional (English) description (ex. "File C:\test.ini not found") |
Status codes:
0 No Errors Found (use status 1 instead!)
1 OK (Default status)
2 Unknown error
3 Panic mode (emergency)
4 Not found (file, configuration, device etc)
5 Access denied
6 Busy
7 Time out / Connection lost
8 Overflow / Can't be reached
9 Checksum error
10 Configuration error
11 Not enough resource (memory, storage etc)
12 Illegal/Unknown instruction (or feature not implemented)
13 Device not ready (starting up)
14 Manual mode (device does not accept commands)
15 Device disabled
16 Device not present
17 Device version not known
18 Hardware failure
19 Exiting / shut down in progress
JHU BRP Robot protocol
JHU BRP Robot protocol description
- Set Workphase (Slicer -> Robot)
- Query and Command (Slicer -> Robot)
- Responses (Robot -> Slicer)
Open questions
- What if the application receives hundreds of "position" packets?
Should we have packet types?
-keep only the last (position)
- all important (command)
- high priority (emergency) - Priority
- Authentication (other than Unique Name)
- Compression?
- Duplicate messages
Resources
- Slicer 3 Image Guided Therapy (IGT) suite
- BioImage Suite VVLink Tool (uses TCL/TK object streaming)
- Meetings concerning Open IGT Link
