ARuler
Mesure distance using apple ARKit
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
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