*camera positions xyz set to: (0,10,30)
*Orbitcontrols target xyz set to: (0,10,0)

console.log(camera.position.distanceTo(controls.target) shows 30
So: the Distance between camera and target is 30

now the problem

this is what I want:

1.- *when distance between camera and target is >=20 orbit target postion.y and camera position.y will remains at 10
2.- *when distance between camera and target is ==10. target postion.y and camera position.y must be 15
3.- *when distance between camera and target is < 20. orbit target and camera will start to increse their position.y values until reach what I said in point two (15). in other words after < 20. target.y and camera position.y will increase in function of the decrease of distance.

I hope you understand me because I know my English is bad.

One thing strikes me though:
you donâ€™t specify what you expect for distances below 10 [units] and above 30 [units] from the target. I sketched two possible outcomes above, visualized as dashed lines. Please specify.

So, what this boils down to, from my point of view is:

the distance â€śdâ€ť between camera and target can be computed as

d = Math.sqrt( camera.x * camera.x + camera.z * camera.z)

And you want to do a LERP of the target.y (and camera.y) , based on the cameraâ€™s distance from the y-axis, between the values 10 and 15.

Thanks for answer. I ask this question over 10 months and I still not full solved.
I did a workaround time ago on my tick() function trying to solved it; works but is not the desired result.

if (this.camera.position.distanceTo(this.controls.target)<=20)
{
this.controls.target.y=15; //head bone position
this.camera.position.y=15;// prevents vertical rotation
this.controls.update();
}
else
{
this.controls.target.y=10; //torso bone
this.controls.update();
}

If you see the video above. When I zooming in and th distance between camera & orbitControls target is below 20 it jumps aggressively instead of gradually being increased (as you showed in your graphic).

About what I expect for distances below 10 UNITS and above 30 UNITS. Nothing I put limits. So user canÂ´t zoom out above 30 UNITS and canÂ´t Zoom in below 10 UNITS.

I will test your code ASAP. Thanks for your help. I really appreciated

Coming back to your problem: Iâ€™ve looked at the video and it matches your code snippet. It may not be what you wanted, but it is exactly what you coded. Hereâ€™s why:

The blue line shows your intended behaviour, the red line shows your implemented behaviour.

Actually you want a continuous transition from the lower-right state (d â‰Ą 20, y = 10) to the upper-left state (d = 10, y = 15). Itâ€™s crucial to understand, that the transition zone comprises both a distance interval and a height interval.

You implemented a mere threshold, an instant switch from y.start to y.end without spreading the height change over the allowed distance interval.

As you enter the transition zone, coming from the lower-right side and following along the blue arrow, youâ€™ll want to increase the y-value at the same rate as youâ€™re consuming the distance zone.

You canâ€™t do that using an if .. else construct. You need to compute the fraction of the distance zone consumed, then add that same fraction of the height zone to the initial height. The following should do the trick:

let dStart = 20;
let dEnd = 10;
let yStart = 10;
let yEnd = 15;
let deltaWidth = dStart - dEnd;
let deltaHeight = yEnd - yStart;
let d, y fract;
...
d = this.camera.position.distanceTo(this.controls.target)
fract = ( dStart - d ) / deltaWidth;
y = fract > 0 ? yStart + fract * deltaHeight : yStart; // LERP only inside transition zone
this.controls.target.y = y; // head bone position
this.camera.position.y = y; // prevents vertical rotation
this.controls.update();

Thanks for your praise, but I would like to deflect that a little bit:
I think Iâ€™m good at explaining things, while the math involved was actually pretty insignificant.