OpenIGTLink/ProtocolV2/Type/TrackingData

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Summary

The TDATA message type is intended for transferring 3D positions of surgical tools, markers etc. Those positions are often measured by optical, electromagnetic or other type of 3D position sensor continuously and transferred as series of messages. Since it is important for software that receives TDATA to control data flow, STT_TDATA query data type has interval field to control the frame rate of consecutive messages.

Message Types

TDATA

Data	Type	Description
NAME_1	char[20]	Name (=Id) of the instrument/tracker
TYPE_1	8 bit unsigned	1: tracker, 2: 6D instrument (regular instrument), 3: 3D instrument (only tip of the instrument defined), 4: 5D instrument (tip and handle are defined, but not the normal vector)
--	8 bit unsigned	Reserved
MATRIX_1	32 bit float	12 values like in TRANSFORM message
...
NAME_N	char[20]	Name (=Id) of the instrument/tracker
TYPE_N	8 bit unsigned	1: tracker, 2: 6D instrument (regular instrument), 3: 3D instrument (only tip of the instrument defined), 4: 5D instrument (tip and handle are defined, but not the normal vector)
--	8 bit unsigned	Reserved
MATRIX_N	32 bit float	12 values like in TRANSFORM message

GET_TDATA

Data

Type

Description

STT_TDATA

Data	Type	Description
Resolution	32 bit unsigned	Minimum time between two frames. Use 0 for as fast as possible. If e.g. 50 ms is specified, the maximum update rate will be 20 Hz.
Coordinate system name	char[32]	Coordinate system to use. Can be empty for default coordinate system. (not included if action = 2)

• All tracking data from one frame is included.
• Invisible/unavailable trackers/instruments are not included.
• Easy to develop. Sample pseudo code: while(true) { recv(trackingdata); updateView(trackingdata); }
• Usually the tracking data will be sent using the standard coordinate system, which is also used for POINT, IMAGE, ... But this does only work after patient registration. Therefore the body of START_PUSH has an optional field for specifing the coordinate system "CAMERA". To switch back to the standard coordinate system, one has to send STOP_PUSH and afterwards START_PUSH without explicitly specifing the camera coordinate system.

STP_TDATA

Data

Type

Description

RTS_TDATA

Data	Type	Description
Status	8 bit unsigned	0: Success 1: Error

Implementations

The TDATA message type is implemented in the following source code.

• igtlTrackingDataMessage.h
• igtlTrackingDataMessage.cxx

Contributors

Alexander Schaal

Comments

Junichi:

• How about adding 8- or 16-bit status field in TDATA? This will allow us to indicate that coordinate system is not registered. I would like to keep START_PUSH message simple....

Alexander:

• What status types can be specified?
• In the case the coordinate system is not valid, a STATUS message should be returned.
• Well, I understand that you would like to keep it as simple as possible. We really like to specifiy the coordinate system like "Camera" or "Patient". We could also specifiy a SET_COORD message, but I think this would be overkill. I still vote for a data specific argument field in START_PUSH. Maybe other future data types can also use this field?
• Due to consistency, I think we should add this field to STOP_PUSH, too.
• We would like to allow only one TDATA push for each client at a time, so a second START_PUSH will stop the first and start the second. A STOP_PUSH will stop the push regardless of the arguments in the body. What do you think about that?

Junichi:

• I haven't defined status types... it can be a bit array like: bit 0: registered or not; bit 1: line-of-site error; ....
  • Do you think it is useful? if not, we can omit it.
• I agree that we need a way to specify coordinate system. It's good idea to have data specific field in the START_PUSH.
• I agree with the last comment. I would say one TDATA push for each device name, because multiple data sources may exist. The coordinate system can be overwritten by another START_PUSH message with the same device name and type.

Alexander:

• I think we don't need the status type. But maybe we define a TDATA in v3 after collecting some feedback from different users. I could think about other fields like diameter of instruments, etc. But for now I would like to keep TDATA as simple as possible.
• Ok, starting another trackingdata push with the same device name will implictly stop the first one. But if another device name is used, a second push will be started.