Skip to main content

Speeding and collision alerts

import MapboxVision
import MapboxVisionSafety
import UIKit

* "Safety alerts" example demonstrates how to utilize events from MapboxVisionSafetyManager
* to alert a user about exceeding allowed speed limit and potential collisions with other cars.

// Custom UIView to draw a red bounding box
class CollisionDetectionView: UIView {
override init(frame: CGRect) {
super.init(frame: frame)

// Transparent view with a red border
backgroundColor = .clear
layer.borderWidth = 3
layer.borderColor =

required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")

class SafetyAlertsViewController: UIViewController {
private var visionManager: VisionReplayManager!
private var visionSafetyManager: VisionSafetyManager!

private let visionViewController = VisionPresentationViewController()

private var alertOverspeedingView: UIView!

private var vehicleState: VehicleState?
private var speedLimits: SpeedLimits?
private var carCollisions = [CollisionObject]()

override func viewDidLoad() {

// Documents directory path with files uploaded via Finder
let documentsPath =
let path = documentsPath.appending("/safety-alerts-drawing")

// create VisionReplayManager with a path to recorded session
visionManager = try? VisionReplayManager.create(recordPath: path)
// register its delegate
visionManager.delegate = self

// create VisionSafetyManager and register as its delegate to receive safety related events
visionSafetyManager = VisionSafetyManager.create(visionManager: visionManager)
// register its delegate
visionSafetyManager.delegate = self

// configure Vision view to display sample buffers from video source
visionViewController.set(visionManager: visionManager)
// add Vision view as a child view

// add view to draw overspeeding alert

override func viewWillAppear(_ animated: Bool) {


override func viewDidDisappear(_ animated: Bool) {


deinit {
// free up VisionSafetyManager's resources

// free up VisionManager's resources

private func addVisionView() {
visionViewController.didMove(toParent: self)

private func addOverspeedingAlertView() {
alertOverspeedingView = UIImageView(image: UIImage(named: "alert"))
alertOverspeedingView.isHidden = true
alertOverspeedingView.translatesAutoresizingMaskIntoConstraints = false
.constraint(equalToSystemSpacingBelow: view.safeAreaLayoutGuide.topAnchor, multiplier: 1),
.constraint(equalToSystemSpacingAfter: alertOverspeedingView.trailingAnchor, multiplier: 1)

// MARK: - Handle VisionSafety events

private func updateCollisionDrawing() {
// remove `CollisionDetectionView` objects from the view
for subview in view.subviews {
if subview.isKind(of: CollisionDetectionView.self) {

// iterate the collection of `CollisionObject`s and draw each of them
for carCollision in carCollisions {
let relativeBBox = carCollision.lastDetection.boundingBox
let cameraFrameSize = carCollision.lastFrame.image.size.cgSize

// calculate absolute coordinates
let bboxInCameraFrameSpace = CGRect(x: relativeBBox.origin.x * cameraFrameSize.width,
y: relativeBBox.origin.y * cameraFrameSize.height,
width: relativeBBox.size.width * cameraFrameSize.width,
height: relativeBBox.size.height * cameraFrameSize.height)

// at this stage, bbox has the coordinates in the camera frame space
// you should convert it to the view space saving the aspect ratio

// first, construct left-top and right-bottom coordinates of a bounding box
var leftTop = CGPoint(x: bboxInCameraFrameSpace.origin.x,
y: bboxInCameraFrameSpace.origin.y)
var rightBottom = CGPoint(x: bboxInCameraFrameSpace.maxX,
y: bboxInCameraFrameSpace.maxY)

// then convert the points from the camera frame space into the view frame space
leftTop = leftTop.convertForAspectRatioFill(from: cameraFrameSize,
to: view.bounds.size)
rightBottom = rightBottom.convertForAspectRatioFill(from: cameraFrameSize,
to: view.bounds.size)

// finally, construct a bounding box in the view frame space
let bboxInViewSpace = CGRect(x: leftTop.x,
y: leftTop.y,
width: rightBottom.x - leftTop.x,
height: rightBottom.y - leftTop.y)

// draw a collision detection alert
let view = CollisionDetectionView(frame: bboxInViewSpace)

private func updateOverspeedingDrawing() {
// when update is completed all the data has the most current state
guard let vehicle = vehicleState, let limits = speedLimits else { return }

// decide whether speed limit is exceeded by comparing it with the current speed
let isOverSpeeding = vehicle.speed > limits.speedLimitRange.max
alertOverspeedingView.isHidden = !isOverSpeeding

extension SafetyAlertsViewController: VisionManagerDelegate {
func visionManager(_ visionManager: VisionManagerProtocol,
didUpdateVehicleState vehicleState: VehicleState) {
// dispatch to the main queue in order to sync access to `VehicleState` instance
DispatchQueue.main.async { [weak self] in
// save the latest state of the vehicle
self?.vehicleState = vehicleState

func visionManagerDidCompleteUpdate(_ visionManager: VisionManagerProtocol) {
// dispatch to the main queue in order to work with UIKit elements
DispatchQueue.main.async { [weak self] in
// update UI elements

extension SafetyAlertsViewController: VisionSafetyManagerDelegate {
func visionSafetyManager(_ visionSafetyManager: VisionSafetyManager,
didUpdateRoadRestrictions roadRestrictions: RoadRestrictions) {
// dispatch to the main queue in order to sync access to `SpeedLimits` instance
DispatchQueue.main.async { [weak self] in
// save currenly applied speed limits
self?.speedLimits = roadRestrictions.speedLimits

func visionSafetyManager(_ visionSafetyManager: VisionSafetyManager,
didUpdateCollisions collisions: [CollisionObject]) {
// we will draw collisions with cars only, so we need to filter `CollisionObject`s
let carCollisions = collisions.filter { $0.object.detectionClass == .car }

// dispatch to the main queue in order to sync access to `[CollisionObject]` array
DispatchQueue.main.async { [weak self] in
// update current collisions state
self?.carCollisions = carCollisions

// This comment is here to assure the correct rendering of code snippets in a public documentation
Was this example helpful?