pitch/yaw/roll

Archives Forums/Blitz3D Bug Reports/pitch/yaw/roll

b32	(Posted 2007) [#1]

Finally I was able to isolate my problem. It is this:

Graphics3D 800, 600, 0, 2
SetBuffer BackBuffer()

pivot = CreatePivot()

RotateEntity pivot, 90, 90, 0

Print EntityPitch(pivot)
Print EntityYaw(pivot)
Print EntityRoll(pivot)

The yaw returns zero. So instead of returning 90,90,0 it returns 90,0,0.
Is this a bug ? Is there a way around this ? Thanks in advance.

markcw

(Posted 2007) [#2]

I think this is called gimbal lock:
http://en.wikipedia.org/wiki/Gimbal_lock

It is a known limitation when using Euler angles ie. it's not a bug. It happens when you try complex rotations. The known way around it is using quaterions. I've no idea how you do that though.

Stevie G

(Posted 2007) [#3]

Definately Gimbal lock ... see this thread for possible solution.

http://www.blitzbasic.com/Community/posts.php?topic=31781

b32	(Posted 2007) [#4]

Aha, so this is the infamous Gimbal lock. Thanks a lot, I used fredborgs solution and it works now.
I also tried getting the pitch/yaw/roll directly from the GetMatElement() matrix, with the help of a routine from leadwerks. For completion, I added both functions:
Thanks again, after hunting me all night, I hope this Gimbal demon is exorcised for good now. :)

Graphics3D 800, 600, 0, 2 
SetBuffer BackBuffer() 

pivot = CreatePivot() 
RotateEntity pivot, 90, 90, 0 

Print "standard:"
Print EntityPitch(pivot) 
Print EntityYaw(pivot) 
Print EntityRoll(pivot) 

Print "fredborgs:"
Print GlobalEntityPitch(pivot)
Print GlobalEntityYaw(pivot)
Print GlobalEntityRoll(pivot)

Print "matrix:"
Print mEntityPitch(pivot)
Print mEntityYaw(pivot)
Print mEntityRoll(pivot)


;fredborg
;post = www.blitzbasic.com/Community/posts.php?topic=31781 <http://www.blitzbasic.com/Community/posts.php?topic=31781> 

Const GIMBAL_LIMIT# = 89.98

Function GlobalEntityPitch#(entity)

	pit# = Int(EntityPitch(entity,True)*1000)/1000.0
	
	Return pit

End Function

Function GlobalEntityYaw#(entity)
	
	pit# = Int(EntityPitch(entity,True)*1000)/1000.0
	yaw# = Int(EntityYaw(entity,True)*1000)/1000.0
	
	If Abs(pit)>GIMBAL_LIMIT
		temp = CreatePivot(entity)
		TurnEntity temp,Sgn(pit)*-90.0,0,0
		yaw# = Int(EntityYaw(temp,True)*1000)/1000.0
		FreeEntity temp
	EndIf

	Return yaw
	
End Function

Function GlobalEntityRoll#(entity)

	pit# = Int(EntityPitch(entity,True)*1000)/1000.0
	rol# = Int(EntityRoll(entity,True)*1000)/1000.0

	If Abs(pit)>GIMBAL_LIMIT
		temp = CreatePivot(entity)
		TurnEntity temp,Sgn(pit)*-90.0,0,0
		rol# = Int(EntityRoll(temp,True)*1000)/1000.0
		FreeEntity temp
	EndIf

	Return rol

End Function

;leadwerks
;post = <a href="http://www.blitzbasic.co.nz/Community/posts.php?topic=21362" target="_blank">http://www.blitzbasic.co.nz/Community/posts.php?topic=21362</a>
Function mEntityPitch#(Entity) 
	Return -ASin(GetMatElement(Entity,2,1)) 
End Function 

Function mEntityYaw#(Entity) 
	Return -ATan2(GetMatElement(Entity,2,0),GetMatElement(Entity,2,2)) 
End Function 

Function mEntityRoll#(Entity) 
	Return ATan2(GetMatElement(Entity,0,1),GetMatElement(Entity,1,1)) ;-ATan2(m(1,0),m(1,1)) 
End Function

(edit)
Because I needed the local angles too, I modified the FredBorg functions. As fas as I can tell they work, but I don't understand exactly how they work I just made them local (to the parent):

Const GIMBAL_LIMIT# = 89.98

Function GlobalEntityPitch#(entity)

	pit# = Int(EntityPitch(entity)*1000)/1000.0
	
	Return pit

End Function

Function GlobalEntityYaw#(entity)
	
	pit# = Int(EntityPitch(entity)*1000)/1000.0
	yaw# = Int(EntityYaw(entity)*1000)/1000.0
	
	If Abs(pit)>GIMBAL_LIMIT
		temp = CreatePivot(entity)
		EntityParent temp, GetParent(entity)
		TurnEntity temp,Sgn(pit)*-90.0,0,0
		yaw# = Int(EntityYaw(temp)*1000)/1000.0
		FreeEntity temp
	EndIf

	Return yaw
	
End Function

Function GlobalEntityRoll#(entity)

	pit# = Int(EntityPitch(entity)*1000)/1000.0
	rol# = Int(EntityRoll(entity)*1000)/1000.0

	If Abs(pit)>GIMBAL_LIMIT
		temp = CreatePivot(entity)
		EntityParent temp, GetParent(entity)
		TurnEntity temp,Sgn(pit)*-90.0,0,0
		rol# = Int(EntityRoll(temp)*1000)/1000.0
		FreeEntity temp
	EndIf

	Return rol

End Function