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Old 05-07-2013, 07:53 AM
4711 4711 is offline
Join Date: Jan 2010
Posts: 15
Fluent viewpoint rotation towards an object

Hi everybody,

I have a simple question:

How can I fluently turn the viz.MainView towards an object somewhere in my environment (without knowing the angle between the current viewing direction and the object)?

I could do all the math behind such a rotation myself, but I guess there's a smarter and much shorter way to achive that with Vizard's built-in methods. What I'm looking for is basically what the "viz.MainView.lookAt" function already does, extended by the possibility for a fluent movement instead of the discrete jump in viewing direction.

Can anybody help me out with a good idea?

Thanks in advance!
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Old 05-07-2013, 09:41 AM
farshizzo farshizzo is offline
WorldViz Team Member
Join Date: Mar 2003
Posts: 2,849
Are you using Vizard 3 or 4?

If you are using Vizard 4, then you can use the vizact.spinTo action to animate the viewpoint to look towards a specific point. Example:
# Animate looking at specified point for half a second
lookAtAction = vizact.spinTo(point=(0,1.8,8),time=0.5,interpolate=vizact.easeOut)

# Add action to main view
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Old 05-07-2013, 10:14 AM
4711 4711 is offline
Join Date: Jan 2010
Posts: 15

thanks for the quick reply. I'm running my script under Vizard 3, since large parts were written before the release of Vizard 4. Unfortunately, it seems like your code doesn't produce the result it's supposed to in Vizard 3.

Is there any other possibility how this could work in Vizard 3?
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Old 05-09-2013, 09:12 AM
farshizzo farshizzo is offline
WorldViz Team Member
Join Date: Mar 2003
Posts: 2,849
You can still use the spinto action in Vizard 3, however you will need to manually calculate the final rotation to spinto. You can do this by saving the main views current rotation, call the lookat function and save the new rotation, then restore the previous rotation.
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Old 05-23-2013, 03:58 AM
4711 4711 is offline
Join Date: Jan 2010
Posts: 15

I can't see how quickly setting the viewpoint towards the object via "lookat()" and then set it back again to the original direction can work without resulting in a short flickering in the viewpoint. Maybe I got you wrong?
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Old 05-23-2013, 04:20 AM
4711 4711 is offline
Join Date: Jan 2010
Posts: 15
I wrote some code myself to solve the problem:

import math
import viz


def Angle2Euler( angle ):
	euler = 0
	# Not defined for negative values
	if angle < 0:
		return 0
	# Calculate 'euler' depending on quadrant
		if angle <= 90:
			# Q1
			euler = 90 - angle
		elif angle <= 270:
			# Q2 & Q3
			euler = -( angle-90 )
			# Q4
			euler = 360 - angle + 90
	return euler

def Cart2Pol( x, y, unit='rad' ):
	# Radius
	r = math.sqrt( math.pow(x,2) + math.pow(y,2) )
	# Angle in [rad]
	t = math.atan2( y ,x )
	# Angle in [deg]
	if unit.lower() == 'deg':
		t = math.degrees( math.atan(float(y)/float(x)) )
		if x < 0:
			t += 180 # Q2 & Q3
		elif x > 0 and y < 0:
			t += 360 # Q4
	return r, t

def LookAt( Target ):

	# Get current position and orientation
	Pos = viz.MainView.getPosition()
	Ori = viz.MainView.getEuler()
	# Define position as 2D point 'P'
	P = [Pos[0], Pos[2]]
	# Define target as 2D point 'T'
	T = [Target[0], Target[2]]
	# Shift 'P' into origin (= 'P0') and
	# move 'T' accordingly (= 'T0')
	T0 = [T[0]-P[0], T[1]-P[1]]

	# Get location of 'T0' as polar angle
	angle = Cart2Pol( T0[0], T0[1], 'deg' )[1]
	# Convert angle to Vizard's Euler style
	euler = Angle2Euler( angle )
	# Create rotation action towards target
	rotation = vizact.spinTo( euler=[euler,0,0], time=2 )
	# Apply rotation to MainView
	viz.MainView.runAction( rotation )

# --- AN EXAMPLE --- #

# Go!

# Add a box behind the MainView
box = viz.add('box.wrl')

# Look at the box
LookAt( box.getPosition() )
This may not be the easiest or most elegant way, but it works!
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fluent, rotation, viewpoint

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