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ARuler

Mesure distance using apple ARKit

中文文档

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Requirements

  • Xcode 9
  • iOS 11
  • An iOS device with an A9 or better processor (iPhone 6s or superior, iPad Pro, iPad 2017)

You should mesure with enough light to detect feature point.

Run

cd to the project folder and run pod install

Instruction

This project use the methods below to determine start and end point.

If detect a point on plane,return it
let planeHitTestResults = sceneView.hitTest(position, types: .existingPlaneUsingExtent)
    if let result = planeHitTestResults.first {

        let planeHitTestPosition = SCNVector3.positionFromTransform(result.worldTransform)
        let planeAnchor = result.anchor

        // Return immediately - this is the best possible outcome.
        return (planeHitTestPosition, planeAnchor as? ARPlaneAnchor, true)
    }
Detect the point from current ARFrame's rawFeaturePoints
  • Get feature points within the frustum combinate with axis that from camera location to screen perspective vanishing point,minimum distance which is 10cm and maximum distance with 3m.
let highQualityfeatureHitTestResults = sceneView.hitTestWithFeatures(position, coneOpeningAngleInDegrees: 5, minDistance: 0.1, maxDistance: 3.0)
  • Fliter the points's discrepancy beyond 3σ.
func fliterWithFeatures(_ features:[FeatureHitTestResult]) -> [SCNVector3] {
    guard features.count >= 3 else {
        return features.map { (featureHitTestResult) -> SCNVector3 in
            return featureHitTestResult.position
        };
    }
        
    var points = features.map { (featureHitTestResult) -> SCNVector3 in
        return featureHitTestResult.position
    }
    // 平均值
    let average = points.average!
    // 方差
    let variance = sqrtf(points.reduce(0) { (sum, point) -> Float in
        var sum = sum
        sum += (point-average).length()*100*(point-average).length()*100
        return sum
        }/Float(points.count-1))
    // 标准差
    let standard = sqrtf(variance)
    let σ = variance/standard
    points = points.filter { (point) -> Bool in
        if (point-average).length()*100 > 3*σ {
            print(point,average)
        }
        return (point-average).length()*100 < 3*σ
    }
    return points
}
  • Determain the plane base on the least-square method.
let detectPlane = planeDetectWithFeatureCloud(featureCloud: warpFeatures)
  • Calculate the crossover point with the plane and the axis.
var planePoint = SCNVector3Zero
if detectPlane.x != 0 {
	planePoint = SCNVector3(detectPlane.w/detectPlane.x,0,0)
}else if detectPlane.y != 0 {
    planePoint = SCNVector3(0,detectPlane.w/detectPlane.y,0)
}else {
    planePoint = SCNVector3(0,0,detectPlane.w/detectPlane.z)
}
    
let ray = sceneView.hitTestRayFromScreenPos(position)
let crossPoint = planeLineIntersectPoint(planeVector: SCNVector3(detectPlane.x,detectPlane.y,detectPlane.z), planePoint: planePoint, lineVector: ray!.direction, linePoint: ray!.origin)
  • If not meet the conditions,return average.
  • If the frustum don't contain any point,return the point nearest to axis.

Reference

Inspired by a video from weibo

Some code adapted fromApple ARKitDemo

Plane fitting method refer to this blog

Communication

Any suggestion or bug please open an issue.

License

ARuler is released under the GPL license.See LICENSE for details.