alert-lib contains classes related to distance estimation, speed calculation, alerts, camera, and AR overlays.

## Distance Estimation

The distance filter estimates the distance of an object from the camera.

The StaticDistanceEstimator class uses an assumed width/height and the camera's properties to determine the camera's distance from an object. The estimator works with cars and pedestrians by default, but may be extended if other objects are needed for your use case. Distances are in meters for default values. For any custom values, the distance unit is the same as the provided size.

public void estimateDistance(List<Recognition> recognitions, Size frameSize, int sensorRotation, float focalLength, SizeF sensorSize)


The following list describes the method parameters:

• recognitions - List of recognitions to process
• frameSize - Size of the image that recognitions were derived from at 0 rotation
• sensorRotation - Clockwise rotation to each frame's natural orientation as a multiple of 90 degrees
• focalLength - Focal length of the capture camera in millimeters
• sensorSize - Size of the physical camera sensor in millimeters

### Note

The distance value for a Recognition may already be available from the ML model.

## RoI - Region of Interest

A Region of Interest (RoI) defines a region of the source image to enable filtering of detections based on their location in the image. For example, when only detections in front of the vehicle are relevant, detections on the far side can be removed.

The SDK defines the following types of regions:

• Primary: This region type typically represents the ego lane
• Secondary: This region type typically represents a region including adjacent lanes on either side of the ego lane

The SDK can generate an RoI via the following methods:

• makeStaticRoi: A static RoI is generated based on vertices defined by the application

### Note

The static RoI vertices must meet the following constraints:

• The vertices must form a convex polygon
• The x and y of each vertex must have a value between 0.0 to 1.0, representing a percentage of the image's width and height, respectively
• makeLaneRoi: The lane RoI is generated based on the output of the Road Lanes model
• The primary region is defined by the 2 ego lane markings
• The secondary region is defined by the adjacent lane markings, if present

### Note

If you are using LSModelManager class for model detection, you have to set the LSModelManager#setRecognitionProcessor() callback so that you can filter results using Roi before they are passed to recognition callback and tracker.

Live Sense SDK supports several types of alerts via the LSDAlertManager class.

### Entry

Entry alerts signal to the application when a detection first enters the primary RoI region.

These alerts support pedestrian detection to alert the driver when a pedestrian has entered the road, and vehicle detection to alert of another vehicle merging into the ego lane.

### Note

This feature is in Beta.

A lane departure alert indicates the subject vehicle is leaving the ego lane and entering the adjacent region.

There are two severity levels of lane departure alerts:

• WARNING: The subject vehicle is likely drifting from their lane rather than intentionally changing lanes.
• INFO: The subject vehicle has departed from the lane.

### Note

For lane departure alerts, the SDK assumes the following:

• The camera is reasonably well centered within the vehicle and facing straight ahead.
• If the camera is placed too far to one side of the vehicle, the SDK may generate false positive alerts.
• The camera has a field of view similar to a phone's wide angle camera
• Ultra wide lenses cause false positive alerts.

### TTC - Time to Collision

Live Sense SDK provides the feature of alerting the user/driver of Time to Collision. This feature helps to avoid accidents and ensure driver safety. This feature is applicable to car, car-brake-light-on, and pedestrian detections in the vehicle's expected path. Time to Collision, or TTC, is calculated as follows:

Time to Collision (T) = -1 * d / ( Δd / Δt ) when Δd < 0

• d = distance to the object
• Δd = change in distance to the object between processed frames
• Δt = change in time between processed frames

This calculation only applies when the distance to an object is decreasing. Otherwise, TTC is infinite and no alert is generated.

LSDAlertManager contains extra heuristics for alerting user of possible hazards in their path. These include time-to-collision with the leading vehicle and people entering the vehicle's direct path.

The following list describes the different severity of alerts based on the value of TTC:

• INFO - If T > 2.5secs
• WARNING - If 1.8secs < T <= 2.5secs
• ALERT - If T <= 1.8secs

These are the default configured values. The values for WARNING and ALERT can be changed by the following methods:

• public void setTimeToCollisionWarning(float timeInSeconds)
• public void setTimeToCollisionAlert(float timeInSeconds)

For LSDAlertManager to fully function it requires the following inputs:

• Certain properties of the camera being used. For more information, see LSDCameraProperties.
• This only needs to be set once per camera setup. This does not include device rotation.
• The vehicle's current speed, normally provided by the device's location services.
• This should be continuously fed in via setCurrentSpeed() using device accelerometer or GPS.
• The latest collection of LSDObjectRecognition.
• Continuously fed in via determineAlerts().

The LSDAlertManager.onAlerts property is available for an asynchronous feed of alerts.

### Usage

Kotlin

val alertManager = LSDAlertManager()
// Can set the minimum speed to activate certain alerts

// Set LSDCameraProperties when camera is initialized or changed
// LSDCamera2Controller provides a LSDCameraProperties instance after LSDCamera2Controller.initialize() is called
// If frame shape is modified (ex. custom cropping), provide a LSDCameraProperties with equally modified sensorSize for accurate proximity alerts
}

// When new speed is available

// When new recognitions are available


Java

LSDAlertManager alertManager = new LSDAlertManager();
// Can set the minimum speed to activate certain alerts

// Set LSDCameraProperties when camera is initialized or changed
// LSDCamera2Controller provides a LSDCameraProperties instance after LSDCamera2Controller.initialize() is called
// If frame shape is modified (ex. custom cropping), provide a LSDCameraProperties with equally modified sensorSize for accurate proximity alerts