Data Range on Joystick.getRawAxis

[danebouchie]

I couldn't find what the range goes to. Is it mesaured in angles (0-360), radians (0-2pi) or -1 to 1? (Java)

[NWChen]

getRawAxis() returns a double in the range -1.0 to 1.0. As a default (joystick centered) the method returns 0.0.

For more information look at the WPILib API courtesy of 2168.

[Joe Ross]

Originally Posted by Signet

getRawAxis() returns a double in the range -1.0 to 1.0. As a default (joystick centered) the method returns 0.0.

For more information look at the WPILib API courtesy of 2168.

I'm curious where you found that information in the javadocs. I couldn't find it.

[NWChen]

Originally Posted by Joe Ross

I'm curious where you found that information in the javadocs. I couldn't find it.

The method summary of getRawAxis() in Joystick links to this source code:

public double getRawAxis(final int axis) {
    return m_ds.getStickAxis(m_port, axis);
}

getStickAxis() is a method of DriverStation:

private DriverStation m_ds;

and in the DriverStation class the getStickAxis() method used with m_ds earlier is as follows:

public double getStickAxis(int stick, int axis) {
       if (axis < 1 || axis > kJoystickAxes) {
           return 0.0;
       }
   
           int value;
           switch (stick) {
                    ...
           default:
               return 0.0;
       }
   
       double result;
       if (value < 0) {
           result = ((double) value) / 128.0;
       } else {
           result = ((double) value) / 127.0;
       }
   
       // wpi_assert(result <= 1.0 && result >= -1.0);
       if (result > 1.0) {
           result = 1.0;
       } else if (result < -1.0) {
           result = -1.0;
       }
    return result;
}

[gluxon]

Originally Posted by Signet

The method summary of getRawAxis() in Joystick links to this source code:

       double result;
       if (value < 0) {
           result = ((double) value) / 128.0;
       } else {
           result = ((double) value) / 127.0;
       }
}

Interesting. I wonder if positive joystick values are expanded (more sensitive) than negative ones looking at this code.

[apalrd]

Originally Posted by gluxon

Interesting. I wonder if positive joystick values are expanded (more sensitive) than negative ones looking at this code.

Not really.

The JS is sent as a signed int (two's compliment) in the UDP packet.

A signed int has a range of -128 to +127. This is because there is no 'negative zero', so there is 1 'extra' count on the negative side since zero is considered a positive number.