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Question by Arch 1 · May 24, 2011 at 01:25 AM · movementworld

Move object based on world position?

I'm assuming this question has already been answered a hundred times before, but I can't seem to find an answer. Upon moving a plane which must move directly forward at a velocity of (0,0,1) in world space at all times, I am unable to keep the plane from losing forward velocity whilst simulating movement via angles. Is there any way to keep the object sustaining at a speed regardless the angle it is moving on?

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avatar image oxium · May 24, 2011 at 02:05 AM 0
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maybe a vector3 normalization issue ? although not sure what you mean / need..

avatar image Wolfram · May 24, 2011 at 02:24 AM 0
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Also, we would need more info about your setup. For example, how do you apply the Z-velocity? Via a rigidbody.velocity? CharacterController? $$anonymous$$oveTo? Or a transform.position+=... in Update()? What do you mean by "simulating movement"? etc.

avatar image Arch 1 · May 24, 2011 at 03:49 AM 0
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I suppose what I'm trying to say is, my object is moving in local space and I'm attempting to move it based on world space. How would I change that? I'm pretty sure that's a REALLY stupid question, but I can't seem to find the answer anywhere.

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Answer by Graham-Dunnett · May 24, 2011 at 09:29 PM

This is just a maths question, right? If your plane is flying in the z direction at 1 unit/second all is good. If if turns and flies at 45 degrees to the z axis and keeps moving at 1unit/second then it's flying at cos(45) in the z axis. (I am basically projecting the new direction onto the z-axis, effectively taking a dot product.) So to maintain a speed of 1 in the z-axis you need to divide by cos(45), or multiply the plane's speed by 1.4. Generalising, as the angle changes to theta adjust the speed by dividing by cos(theta). (Since cos always returns a value less than one, dividing by cos(theta) will always increase the plane's speed.)

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Answer by iantlloyd · May 26, 2011 at 04:34 AM

This will move it along the Z world axis. I'm not sure how well this works with most things though. Works if your object is always changing its local rotations and what not.

var speed : float = 5.0;

function Update() {

directionForward = Vector3.forward Time.deltaTime speed;

transform.Translate(directionForward, Space.World);

}

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