dynamic - Locator following other locator in DynamicModule

I'm trying to create a dynamic environment where I specify, using two locators, the initial condition (position (x,y) and velocity angle (alpha)) of a 2D particle.

To simplify, I'm assuming the initial position is restricted to a circle, and the velocity angle is always in respect to an angle in relation to the normal vector, perpendicular to the tangent vector.

This means that in the end, I would like to have 3 parameters: x,y initial position of the positional locator, and an initial angle, defined as the angle between the vector (positional locator - angle locator) and the normal vector.

The main problem resides on the coupling between the positional locator, and the angle locator: when I move the positional locator, I would like to have the angle locator moved in such a way that the initial angle is preserved.

To manipulate those, I'm using two Locators: one for position (initialPoint), one for initial angle (pt2)

DynamicModule[{initialPoint = {0, 0}, pt2 = {0, 0}},
 Style[Graphics[{
    Dashed,
    Circle[{0, 0}, 1],
    Locator[
     Dynamic[pt2, (pt2 = 
         initialPoint + 0.5 Normalize[# - initialPoint]) &]], 
    Locator[Dynamic[initialPoint, (initialPoint = Normalize[#]) &]]}, 
   PlotRange -> {{-3.3, 3.3}, {-3.3, 3.3}}, AspectRatio -> 1], 

  Selectable -> False]]

however, when I dynamically pick the initialPoint, the second locator does not follow it. What can I do it in order to keep pt2 always such that the initial angle is preserved?

Comments

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