ronaldobandeira / arkitdepthfindsurfaceweb

ARKitDepthFindSurfaceWeb

Abstract

ARKitDepthFindSurfaceWeb is a demo application developed by CurvSurf for accumulate point cloud from depth map of Apple LiDAR, and find 5 primitive shapes (plane, sphere, cylinder, cone, torus) from that with our FindSurface Web API.

How to use Program

1. Press Record button if you want to start recording (collection) depth points.
2. After recording is finished (when press the Stop button),
3. Select primitive type you want to find.
4. Press Find button and wait for a result.

NOTE: You can export accumulated point cloud data to text format by pressing export button (blue icon on upper right corner next to a motion reset button).

Methods to consider

1. How to convert depth map to world coordinates

// Parameters from ARFrame
let localToWorld            : matrix_flaot4x4 // Calculated With Camera Extrinsic Parameter
let cameraIntrinsicsInversed: matrix_float3x3
let cameraResolution        : vector_float2
let depthMapResolution      : vector_float2

let x: Float // x-coordinate of the depth map
let y: Float // y-coordinate of the depth map
let d: Float // depth value of [x, y] coordinates of depth map

let scaleFactor = cameraResolution / depthMapResolution
let localPoint = cameraIntrinsicsInversed 
               * (vector_float3( x * scaleFactor.x, y * scaleFactor.y, 1 ) * d)
let worldPoint = localToWorld * vector_float4( localPoint, 1 )

Note that: CameraIntrinscsInversed, Camera Resolution, DepthMap Resolution and [x, y] coordinates will never be changed through entire application life cycle. Due to remove redundant work, we have made a calculation of dealing these data: GridElement.

// SampleExtension.swift

struct GridElement {
    let x: Int  // X-coordinate of the depth map
    let y: Int  // Y-coordinate of the depth map
    let base: simd_float3 // pre-calculated parameter of [x, y]
    
    // ...omitted...

    static func makeDepthGrid( /* ...omitted... */ ) {
        // ...omitted...
        // Pre-calculation with camera intrinsic parameters here...
        grid.append( GridElement(
            x,
            y,
            cameraIntrinsicsInversed * simd_make_float3( x * rx, y * ry, 1 )
        ) )
        // ...omitted...
    }
}

2. Accumulate Point Cloud

// ViewController.swift

// ln:448
private func accumulatePoints(frame: ARFrame) {
    // ...omitted...

    // Get Camera Parameters
    let camera = frame.camera
    let localToWorld = camera.viewMatrix(for: .landscapeRight).inverse
                     * CameraHelper.makeRotateToARCameraMatrix(orientation: .landscapeRight)
    
    // Get DepthMap
    let frame.sceneDepth.depthMap // or frame.smoothedSceneDepth.depthMap

    // ...omitted...

    // Make Grid Element with Camera Intrinsic Parameter
    // This will be executed only once for initializing.
    let cameraIntrinsicsInversed = camera.intrinsics.inverse // mat3x3
    let cameraResolution         = camera.imageResolution
    depthGrid = GridElement.makeDepthGrid( depthWidth, depthHeight,
                                           cameraIntrinsicInversed: cameraIntrinsicsInversed,
                                           cameraResolution: cameraResolution )

    // ...omitted...

    // Random Sampling Grid Points
    let gridList = depthGrid.sample( UInt(sampleCount) )

    // ...omitted...

    // Depth Map to Point Cloud
    for g in gridList{
        // ...omitted...

        // 1. Get Depth Value From DepthMap on [g.x, g.y] coordinates
        let d = Float((depthData.advanced(by: g.y * depthStride).assumingMemoryBound(to: Float32.self))[g.x])

        // 2. Converting Depth Value to Local 3-D Point (with camera intrinsic parameters)
        let local = simd_make_float4( g.base * Float(d), 1 );

        // 3. Local Coordinates to World Coordinates (with camera extrinsic parameters)
        let worldPoint = localToWorld * local;

        // ...omitted...
    }
}

3. Request FindSurface

// ViewController.swift

// ln:696
@IBAction func onClickMainActionButton(_ sender: Any) {
    // ...omitted...
    runFindSurfaceAsync(
        onSuccess: { (result, extra) -> Void in 
            // TODO: when success
        },
        onFail: { (error) -> Void in 
            // TODO: when fail
        },
        onEnd: { () -> Void in
            // TODO: when all task is done (either success or fail)
        }
    )
    // ...omitted...
}

// See also runFindSurfaceAsync() method on ln:594

NOTE: See FindSurfaceWeb.swift for actual request process and handling result data.

License

This project is licensed under the MIT License. Copyright 2021 CurvSurf.