Omni Velocity information

[M@rcello]

Hi, do you know if there is the chance to get the velocity information from the Omni.
The problem is that i have attacched a ball to the omni, and i am able to control the pose of the ball with it.
What i want to do is to use velocity like trigger to send forces from the device to the operator.

This is my code:
import viz
import hd
import vizinfo
import time
import math
import cmath
from datetime import datetime


viz.go()

ball=viz.add('white_ball.wrl')

viz.MainView.setPosition([0,-0.5,-5])

hd.marker(ball)

start_box=viz.add('box.wrl')
start_box.setPosition([2.5,-0.7,3])
start_box.color([0,256,0])
start_box.setScale([0.5,0.5,0.5])

start_box.collideBox()

finish_box=viz.add('box.wrl')
finish_box.setPosition([-2.5,-0.7,3])
finish_box.setScale([0.5,0.5,0.5])

finish_box.collideBox()

pos_goal=[2.35,-0.4,0]

#print pos_new[0],pos_new[1],pos_new[2]

vizinfo.add('To start reach the green zone and then reach the red one')

error=[0,0,0]
vel=[0,0,0]
Kp=([0.05,0,0],[0,0.05,0],[0,0,0.05])
pos_hidden=[0,0,0]

def print_pos():
t1 = current_milli_time()
delay=t1-t0
print delay
if (delay>3000):
for i in range(0,3):
pos=hd.get(hd.POSITION)
error[i]=-pos_goal[i]+pos_hidden[i]
vel[i]=-Kp[i][i]*error[i]
pos_hidden[i]=pos_hidden[i]+vel[i]

ce = hd.ConstantEffect(dir=[pos_hidden[0]-pos[0],pos_hidden[1]-pos[1],0],mag=0.2)
ce.trigger(0.2)

# print pos_goal[0],pos_goal[1],pos_goal[2]
# print error[0],error[1],error[2]
# print vel[0],vel[1],vel[2]
# print pos_hidden[0],pos_hidden[1],pos_hidden[2]

current_milli_time = lambda: int(round(time.time() * 1000))

def start():
global t0
t0 = current_milli_time()
vizact.ontimer(0.1,print_pos)
vizact.onkeydown(' ',start)

Thanks in advance!!

[Jeff]

Do you mean the velocity of the stylus as the operator moves it or something else?

[M@rcello]

I would like to have information about the phantom's velocity during the motion!
I want to use it as a trigger,like:

Before sending forces check if in the last 3 seconds the velocity(x,y,z) was zero->in that case send forces otherwise wait!

I would like to now if there is already something like the hd.POSITION but for the velocity!

[Jeff]

It does not look like there is a velocity command. The available commands can be found in the Sensable (http://docs.worldviz.com/vizard/#SensAble_Haptic_Devices.htm) and standard sensor (http://docs.worldviz.com/vizard/#Sensors.htm) pages in the Vizard help. You could calculate the velocity between frames or some other time interval. For example:

import viz
import vizact
import vizmat

viz.go()
viz.addChild('piazza.osgb')
device = sensable.addHapticDevice()

lastPos = [0,0,0]
def calculateVelocity():
global lastPos
pos = device.getPosition()
distance = vizmat.Distance(lastPos,pos)
velocity = distance/viz.elapsed()
lastPos = pos

vizact.ontimer(0.1,calculateVelocity)

[M@rcello]

First of all thanks for your interest.

I thougth about this solution and in this case it could work.
The problem is:what happens when i need velocity information in real time during a task?
What I am trying to say is that velocity computed in this way could be affected by rumors,it means that i have to filter the information obtained.

What do you think?

[Jeff]

You could calculate the velocity from one frame to the next using the following:

lastPos = [0,0,0]
def calculateVelocity():
global lastPos
pos = device.getPosition()
distance = vizmat.Distance(lastPos,pos)
velocity = distance/viz.getFrameElapsed()
lastPos = pos

vizact.onupdate(0,calculateVelocity)

[Robin]

Hello @Jeff & @Marcello,

since this thread is a little bit older, I wanted to know, if there is a update regarding the velocity issue.

I'm am working on a Virtual Track in WorldViz with STOP-signs, where the user is instructed to stop. Whether he does so, I wanted to controll with the help of a proximity sensor. The requirements for a successful "stop" should be "reached sensor" and "velocity = 0".

Within the vizard help I found the command getVelocity(), which only works with <node3D>. Is it somehow possible to get the velocity of the user (or rather the MainView)?

Best regards
Robin

[Jeff]

Here's an example that prints out the viewpoint velocity each frame:

import viz
viz.go()

viz.addChild('piazza.osgb')

lastPos = [0,0,0]
def calculateVelocity():
global lastPos
pos = viz.MainView.getPosition()
distance = vizmat.Distance(lastPos,pos)
velocity = distance/viz.getFrameElapsed()
print velocity
lastPos = pos

vizact.onupdate(0,calculateVelocity)