Proximity Sensor

1. Introduction

The Proximity Sensor extends the Generic Sensor API [GENERIC-SENSOR] to provide information about proximity level, as detected by the device’s primary proximity sensor. The proximity level is reported as the distance (in centimeter) from the sensor to the closest visible surface. § 9 Limitations of Proximity Sensors describes more about the potential limitations, why the precise distance value reported by different devices can be different, due to differences in detection method, sensor construction, etc. Moreover some proximity sensors might be only able to provide just a boolean to indicate if there is a physical object which is near, more like presence detection, than an absolute value for the distance.

2. Examples

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

sensor.onreading = () => console.log(sensor.distance);

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

3. Security and Privacy Considerations

Proximity sensor provides information about closeness of the sensor to nearby objects, thus, may expose privacy sensitive information for user identifying and/or fingerprinting attacks.

To mitigate these, user agents should use one or both of the following mitigation strategies:

reduce accuracy of a sensor reading
limit maximum sampling frequency

These mitigation strategies complement the generic mitigations defined in the Generic Sensor API [GENERIC-SENSOR].

4. Permissions Policy integration

This specification defines a policy-controlled feature identified by the string "proximity-sensor". Its default allowlist is "self".

5. Model

The Proximity Sensor sensor type has the following associated data:

Extension sensor interface: ProximitySensor
Sensor permission names: "proximity"
Sensor feature names: "proximity-sensor"
Permission revocation algorithm: Invoke the generic sensor permission revocation algorithm with "proximity".
Default sensor: The device’s main proximity detector.
Virtual sensor type: "proximity"

A latest reading for a Sensor of Proximity Sensor sensor type includes three entries whose keys are "distance", "max", "near" and whose values contain distance, max and near values.

The distance is a value that represents the distance between a device and the closest visible surface of the physical object within the sensing range. Its unit is the centimeter (cm).

The max is a value that represents the maximum sensing range of the main proximity detector, in centimeters.

The near is a value that represent the presence of a visible surface in the vicinity of the main proximity detector.

6. API

6.1. The ProximitySensor Interface

[SecureContext, Exposed=Window]
interface ProximitySensor : Sensor {
  constructor(optional SensorOptions sensorOptions = {});
  readonly attribute double? distance;
  readonly attribute double? max;
  readonly attribute boolean? near;
};

To construct a ProximitySensor object the user agent must invoke the construct a proximity sensor object abstract operation.

6.1.1. The distance attribute

The distance attribute of the ProximitySensor interface returns the result of invoking get value from latest reading with this and "distance" as arguments.

If the physical object is outside the sensing range, the attribute must return null.

6.1.2. The max attribute

The max attribute of the ProximitySensor interface returns the result of invoking get value from latest reading with this and "max" as arguments.

6.1.3. The near attribute

The near attribute of the ProximitySensor interface returns the result of invoking get value from latest reading with this and "near" as arguments.

If the physical object is outside the sensing range, the attribute must return null.

Note: If the implementation is unable to provide the near value, it could infer the near value from the value of distance. For example, if distance is not equal to max, it could imply there is a physical object in the sensing range.

7. Abstract Operations

7.1. Construct a proximity sensor object

input: options, a SensorOptions object.
output: A ProximitySensor object.

Let allowed be the result of invoking check sensor policy-controlled features with ProximitySensor.
If allowed is false, then:
1. Throw a SecurityError DOMException.
Let proximity_sensor be the new ProximitySensor object.
Invoke initialize a sensor object with proximity_sensor and options.
Return proximity_sensor.

8. Automation

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

The per-type virtual sensor metadata map must have the following entry:

key: "proximity"
value: A virtual sensor metadata whose reading parsing algorithm is the proximity reading parsing algorithm.

8.1. Proximity reading parsing algorithm

input: parameters, a JSON Object
output: A sensor reading or undefined

Let reading be a new sensor reading.
Let keys be the list « "distance", "max" ».
For each key of keys
1. Let value be the result of invoking parse single-value number reading with parameters and key.
  1. If value is undefined.
    1. Return undefined.
2. Set reading[key] to value[key].
Let near be the result of invoking get a property from parameters with "near".
1. If near’s type is not Boolean
  1. Return undefined.
2. Set reading["near"] to near.
Return reading.

9. Limitations of Proximity Sensors

Since most proximity sensors detect electromagnetic radiation (e.g., an infrared light or a magnetic field), certain material properties can interfere with the sensor’s ability to sense the presence of a physical object. Things that can interfere with a sensor include, but are not limited to, the material’s translucency, reflectiveness, color, temperature, chemical composition, and even the angle at which the physical object is reflecting the radiation back at the sensor. As such, proximity sensors should not be relied on as a means to measure distance. The only thing that can be deduced from a proximity sensor is that a physical object is somewhere in the distance between the minimum sensing distance and the maximum sensing distance with some degree of certainty.

10. Acknowledgements

Tobie Langel for the work on Generic Sensor API and inputs on this specification. Doug Turner for the initial prototype and Marcos Caceres for the test suite.

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]

Proximity Sensor

Abstract

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