How to find the angle of a point on a circle

[Sindious]

Im scripting a system where a speedometer is automatically generated and Im working on a script that generates the pointers. The positioning works fine however they do not rotate how I want them to.

Example: I want to find angle x

Each grey box is a pointer that needs to be angled relative to it’s position on the circle

Script:

local Player = game.Players.LocalPlayer
local Character = Player.Character

local TextLabel = script.Parent
local Needle = script.Parent.Parent.Parent.Right.SpeedWheel.Needle

-- Needle
local maxSpeed = 170
local minAngle,maxAngle = 45,315

local totalDegrees = maxAngle-minAngle
local speedPerDegree = totalDegrees/maxSpeed

local function calculateDegree(speed)
	return math.min(minAngle+speed*speedPerDegree,maxAngle)
end


-- Speedometer
local radius = 0.5 -- half of a thing in ui terms

local function calculatePointerDegree(x, y)
	return math.deg(math.atan2(x, y))
end

local function getXAndYPositions(r, angle)
	local x = math.sin(math.rad(angle)) * r
	local y = math.cos(math.rad(angle)) * r
	
	return x, y
end

local function newPointer(angle, speed)
	local BigPointer = Instance.new("Frame", Needle.Parent)
	BigPointer.AnchorPoint = Vector2.new(0.5, 0.5)
	BigPointer.Size = UDim2.new(0.05, 0,0.02, 0)
	BigPointer.Name = "MajorPointer"
	BigPointer.BackgroundColor3 = Color3.fromRGB(255, 255, 255)
	BigPointer.BackgroundTransparency = 0.2
	BigPointer.BorderSizePixel = 0
	
	local x, y = getXAndYPositions(radius, angle)
	BigPointer.Position = Needle.Parent.Position + UDim2.new(x, 0, y, 0)
	BigPointer.Rotation = calculatePointerDegree(x, y) -- PROBLEM
end

task.spawn(function()
	while task.wait(0.01) do
		local Speed = math.floor(Character.HumanoidRootPart.AssemblyLinearVelocity.Magnitude/1609.344/3.571*3600)
		local deg = calculateDegree(Speed)

		TextLabel.Text = Speed
		Needle.Rotation = deg
	end
end)


for i = 10, maxSpeed, 10 do
	local degree = calculateDegree(i)
	newPointer(degree, i)
end

[happya_x (Happya)]

You don’t have to use atan to find the angle since you already have the angle

Try adding offsets of multiples of 90 if it’s still off

[Sindious]

That didn’t really help it just put them in random rotations again.

[happya_x (Happya)]

I think it looks like its turning the wrong direction as it moves along the circle

Maybe try multiplying the rotation by -1

[Sindious]

I tried math.deg(math.atan2(-x, -y)) but it gave this result

[Sindious]

I fixxed it myself I didn’t need to do this complex math in the first place I just had to make my UI in a clever way so I just had to modify the rotation to achieve this effect