atan2()

[Math]

double atan2(double y, double x);

Description

Returns the principal value of the arc tangent of $\frac{y}{x}$ in radians, using the signs of both arguments to determine the quadrant of the return value.

Parameters

x: The x-coordinate of the point.

y: The y-coordinate of the point.

Returns

The principal value of the arc tangent of $\frac{y}{x}$ in radians.

Example Code

The code reads the values of two potentiometer connected to pins INY and INX and place the tangent to the pin OUT.

void setup() {
    pinLabel(0, "INY");  // set the label of pin 0 to "INY"
    pinLabel(1, "INX");  // set the label of pin 1 to "INX"
    pinLabel(2, "OUT");  // set the label of pin 2 to "OUT"
    pinMode(2, OUTPUT);  // set pin 2 as output

    pinLabel(3, "VCC");  // set the label of pin 3 to "VCC"
    powerPin(3);         // set pin 3 as power pin
    pinLabel(4, "GND");  // set the label of pin 4 to "GND"
    groundPin(4);        // set pin 4 as ground pin
}

void loop() {
    // read the value of the potentiometers
    int val_x = analogRead(0);
    int val_y = analogRead(1);
    // map the values to the range of 0 to 180
    double angle_y = map(val_x, 0, 1023, 0, 180);
    double angle_x = map(val_y, 0, 1023, 0, 180);
    // calculate the arc tangent of the angle in radians
    double atan2Val = atan2(angle_x * PI / 180, angle_y * PI / 180);
    // map the value to the range of 0 to 1023
    analogWrite(2, (int) atan2Val * 1023);
    // delay for 100ms
    delay(100);
}

Notes and Warnings

The angle should be in radians. To convert the angle from degrees to radians, multiply the angle by PI / 180.
The output value is in the range of −π to π.