ARuler

Mesure distance using apple ARKit

ENGLISH README

预览

运行

cd到工程目录下，运行pod install

安装

因为ARKit使用限制，设备要求为6s以上，系统最低要求为iOS11，Xcode版本为9以上

测量时需保证光线充足

问题

ARKit目前只能识别水平的平面，所以只能测量水平面的长度，不能测量垂直平面上的长度，不知道视频里的是怎么实现的，有知道的小伙伴可以一起交流一下

去除了识别平面后才进行测量的逻辑，采用最近的特征点，可以测量垂直的物体啦

说明

项目中确定起始和结束点的位置主要有以下几种

如果存在检测到的平面，返回平面上一点

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)
    }

根据当前ARFrame中的rawFeaturePoints计算点

• 获取以摄像头和屏幕上一点对应的透视消失点为轴，角度为10度，最小距离为10cm，最大距离为三米组成的截锥体内的特征点

let highQualityfeatureHitTestResults = sceneView.hitTestWithFeatures(position, coneOpeningAngleInDegrees: 5, minDistance: 0.1, maxDistance: 3.0)

• 假设抽样的特征点符合正态分布，过滤偏差值大于 3σ 的值

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
}

• 根据过滤的点用最小二乘法进行平面推定

let detectPlane = planeDetectWithFeatureCloud(featureCloud: warpFeatures)

• 根据截锥体轴上的点和向量及平面上的点和法向量计算交点

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)

• 如果直线和平面平行或不符合平面推定条件，返回点平均值
• 如果截锥体内没有符合的点，查找出距离轴最近的点

参考

看到微博上AR虚拟尺子视频，就想试着模仿着实现一下

部分代码来自苹果ARKitDemo

平面拟合代码参考这篇博客

建议

有任何建议或问题请提issue

开源协议

ARuler开源在 GPL 协议下，详细请查看 LICENSE 文件