Chief Delphi - Data Range on Joystick.getRawAxis

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danebouchie

18-02-2014 20:24

Data Range on Joystick.getRawAxis

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

18-02-2014 20:36

Re: Data Range on Joystick.getRawAxis

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

19-02-2014 04:36

Re: Data Range on Joystick.getRawAxis

Quote:

Originally Posted by Signet (Post 1345598)

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

19-02-2014 08:58

Re: Data Range on Joystick.getRawAxis

Quote:

Originally Posted by Joe Ross (Post 1345859)

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:

Code:

public double getRawAxis(final int axis) {

    return m_ds.getStickAxis(m_port, axis);

}

getStickAxis() is a method of DriverStation:

Code:

private DriverStation m_ds;

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

Code:

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

19-02-2014 09:03

Re: Data Range on Joystick.getRawAxis

Quote:

Originally Posted by Signet (Post 1345918)

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

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

19-02-2014 09:54

Re: Data Range on Joystick.getRawAxis

Quote:

Originally Posted by gluxon (Post 1345923)

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.

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