Gyroscope

1. Introduction

The Gyroscope API extends the Generic Sensor API [GENERIC-SENSOR] to provide information about the angular velocity around the device’s local X, Y and Z axis in terms of radian per seconds units.

2. Use Cases and Requirements

The use cases and requirements are addressed in the Motion Sensors Explainer document.

3. Examples

let sensor = new Gyroscope();
sensor.start();

sensor.onreading = () => {
    console.log("Angular velocity around the X-axis " + sensor.x);
    console.log("Angular velocity around the Y-axis " + sensor.y);
    console.log("Angular velocity around the Z-axis " + sensor.z);
};

sensor.onerror = event => console.log(event.error.name, event.error.message);

4. Security and Privacy Considerations

Sensor readings provided by inertial sensors, such as gyroscope, could be used by adversaries to exploit various security threats, for example, keylogging, location tracking, fingerprinting, user identifying and even eavesdropping.

Research papers published by security community, for instance, [KEYSTROKEDEFENSE], indicate that by throttling the frequency, risks of successful attacks are not fully eliminated, while throttling may greatly affect usefulness of a web application with legitimate reasons to use the sensors.

The [TOUCHSIGNATURES] research paper proposes that implementations can provide visual indication when inertial sensors are in use and/or require explicit user consent to access sensor readings. These mitigation strategies complement the generic mitigations defined in the Generic Sensor API [GENERIC-SENSOR].

5. Permissions Policy integration

This specification utilizes the policy-controlled feature identified by the string "gyroscope" defined in [DEVICE-ORIENTATION].

6. Model

The Gyroscope sensor type has the following associated data:

Extension sensor interface

Gyroscope

Sensor permission names

"gyroscope" (defined in [DEVICE-ORIENTATION])

Sensor feature names

"gyroscope" (defined in [DEVICE-ORIENTATION])

Permission revocation algorithm

Invoke the generic sensor permission revocation algorithm with "gyroscope".

Default sensor

The device’s main gyroscope sensor.

Virtual sensor type

"gyroscope"

A latest reading of a Sensor of Gyroscope sensor type includes three entries whose keys are "x", "y", "z" and whose values contain current angular velocity about the corresponding axes.

The angular velocity is the rate at which the device rotates about a specified axis in a local coordinate system defined by the device. Its unit is the radian per second (rad/s) [SI].

The sign of the current angular velocity depends on the rotation direction and it must be according to the right-hand convention in a local coordinate system defined by the device, such that positive rotation around an axis is clockwise when viewed along the positive direction of the axis (see figure below).

6.1. Reference Frame

The local coordinate system represents the reference frame for the Gyroscope readings. It can be either the device coordinate system or the screen coordinate system.

7. API

7.1. The Gyroscope Interface

[SecureContext, Exposed=Window]
interface Gyroscope : Sensor {
  constructor(optional GyroscopeSensorOptions sensorOptions = {});
  readonly attribute double? x;
  readonly attribute double? y;
  readonly attribute double? z;
};

enum GyroscopeLocalCoordinateSystem { "device", "screen" };

dictionary GyroscopeSensorOptions : SensorOptions {
  GyroscopeLocalCoordinateSystem referenceFrame = "device";
};

Supported sensor options for Gyroscope are "frequency" and "referenceFrame".

7.1.1. Gyroscope.x

The x attribute of the Gyroscope interface represents the current angular velocity around X-axis. In other words, this attribute returns the result of invoking get value from latest reading with this and "x" as arguments.

7.1.2. Gyroscope.y

The y attribute of the Gyroscope interface represents the current angular velocity around Y-axis. In other words, this attribute returns the result of invoking get value from latest reading with this and "y" as arguments.

7.1.3. Gyroscope.z

The z attribute of the Gyroscope interface represents the current angular velocity around Z-axis. In other words, this attribute returns the result of invoking get value from latest reading with this and "z" as arguments.

8. Abstract Operations

8.1. Construct a Gyroscope object

9. Automation

This section extends Generic Sensor API § 9 Automation by providing Gyroscope-specific virtual sensor metadata.

The gyroscope virtual sensor type and its corresponding entry in the per-type virtual sensor metadata map are defined in DeviceOrientation Event Specification § automation.

10. Acknowledgements

Tobie Langel for the work on Generic Sensor API.

11. Conformance

Conformance requirements are expressed with a combination of descriptive assertions and RFC 2119 terminology. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this document are to be interpreted as described in RFC 2119. However, for readability, these words do not appear in all uppercase letters in this specification.

All of the text of this specification is normative except sections explicitly marked as non-normative, examples, and notes. [RFC2119]

A conformant user agent must implement all the requirements listed in this specification that are applicable to user agents.

The IDL fragments in this specification must be interpreted as required for conforming IDL fragments, as described in the Web IDL specification. [WEBIDL]