Treadmill , Optotrak & Vizard

[Canucks]

We are trying to run Vizard for Optotrak in which the participant walk on the treadmill. The problem is since it's on a treadmill, on Vizard it shows it as going back & forth ( not moving forward) since the coordinates are not changing ( ir: you go from (0,0,1) to (0,0,2) even if you go 10K on treadmill). Is there way to fix this issue?

[Jeff]

Use vizconnect to configure the viewpoint to move with optotrack data. Add a group tracker above the headtracker in the vizconnect scenegraph and update the group's position in the script that imports the vizconnect config file based on the treadmill speed. Take a look at all the vizconnect tutorials (http://docs.worldviz.com/vizard/#vizconnect_tutorial_displays_and_trackers.htm) to get started if you're not familiar with vizconnect.

[Canucks]

Thank you for your reply. I created group tracker in the vizconnect. I'm wondering how can we read treadmill speed to update my mainview position? Are you suggesting let's say treadmill speed is 2 MPH, should I update the position based on that?

[Jeff]

I'm not sure how you would get the treadmill data in Vizard. Does the manufacturer provide a Python API? If so, you could use that to get the data into Vizard. Attached is an example that updates a group tracker every frame to move the viewpoint.

[Canucks]

Hi Jeff,
what is unit for scale in vizard? m/s?

[Jeff]

Can you describe further the code you are referring to that's scaling the movement?

[Canucks]

You sent me the simulated treadmill .. i'm wondering what's the unit of speed is so I can adjust with ours
TREADMILL_SPEED = .05

viz.add('sky_day.osgb')

# Add ground model 20 times
for i in range (20):
viz.addChild('ground_grass.osgb', cache = viz.CACHE_CLONE, pos = [0,0.01,i+25])

groupTracker = vizconnect.getTracker('treadmill_node').getRaw()

def updateGroup():
groupTracker.setPosition([0,0,TREADMILL_SPEED],viz.REL_LOCAL)

vizact.onupdate(0,updateGroup)

[Jeff]

The following code allows you to specify the speed in meters per second:

# Speed in meters per second
SPEED = 1

def updateGroup():
# Get the elapsed time since the previous frame and multiply that against the speed in m/s
groupTracker.setPosition([0,0,SPEED * viz.getFrameElapsed()],viz.REL_LOCAL)

vizact.onupdate(0,updateGroup)