ARKIT

Question

所以我了解到，为了跟踪图像，我们需要创建一个 AR 资源文件夹并将我们打算跟踪的所有图像放在那里，以及通过检查器配置它们的真实世界大小属性。

然后我们将 ARReferenceImages 数组设置为 Session 的 World Config。

一切都很好。但是我们可以追踪多少？ 10？ 100？ 1000000？是否可以下载这些图像并即时创建 ARReferences，而不是从一开始就将它们放在捆绑包中？

Answer 1

查看 Apple Docs 它似乎没有指定限制。因此，它很可能会假设它可能取决于内存管理等。

关于即时创建图像，这绝对是可能的。

根据文档，这可以通过以下两种方式之一完成：

从 Core Graphics 图像对象创建新的参考图像：

init(CGImage, orientation: CGImagePropertyOrientation, physicalWidth: CGFloat)

从 Core Video 像素缓冲区创建新的参考图像：

init(CVPixelBuffer, orientation: CGImagePropertyOrientation, physicalWidth: CGFloat)

这是一个使用标准 Assets Bundle 中的图像动态创建 referenceImage 的示例，尽管这可以很容易地适应解析来自 URL 等的图像：

// Create ARReference Images From Somewhere Other Than The Default Folder
func loadDynamicImageReferences(){

//1. Get The Image From The Folder
guard let imageFromBundle = UIImage(named: "moonTarget"),
//2. Convert It To A CIImage
let imageToCIImage = CIImage(image: imageFromBundle),
//3. Then Convert The CIImage To A CGImage
let cgImage = convertCIImageToCGImage(inputImage: imageToCIImage)else { return }

//4. Create An ARReference Image (Remembering Physical Width Is In Metres)
let arImage = ARReferenceImage(cgImage, orientation: CGImagePropertyOrientation.up, physicalWidth: 0.2)

//5. Name The Image
arImage.name = "CGImage Test"

//5. Set The ARWorldTrackingConfiguration Detection Images Assuming A Configuration Is Running
configuration.detectionImages = [arImage]

}


/// Converts A CIImage To A CGImage
///
/// - Parameter inputImage: CIImage
/// - Returns: CGImage
func convertCIImageToCGImage(inputImage: CIImage) -> CGImage? {

let context = CIContext(options: nil)
if let cgImage = context.createCGImage(inputImage, from: inputImage.extent) {

 return cgImage

}

return nil
}

然后我们可以在 ARSCNViewDelegate 内进行测试，例如

func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {

//1. If Out Target Image Has Been Detected Than Get The Corresponding Anchor
guard let currentImageAnchor = anchor as? ARImageAnchor else { return }

let x = currentImageAnchor.transform
print(x.columns.3.x, x.columns.3.y , x.columns.3.z)

//2. Get The Targets Name
let name = currentImageAnchor.referenceImage.name!

//3. Get The Targets Width & Height In Meters
let width = currentImageAnchor.referenceImage.physicalSize.width
let height = currentImageAnchor.referenceImage.physicalSize.height

print("""
Image Name = \(name)
Image Width = \(width)
Image Height = \(height)
""")

//4. Create A Plane Geometry To Cover The ARImageAnchor
let planeNode = SCNNode()
let planeGeometry = SCNPlane(width: width, height: height)
planeGeometry.firstMaterial?.diffuse.contents = UIColor.white
planeNode.opacity = 0.25
planeNode.geometry = planeGeometry

//5. Rotate The PlaneNode To Horizontal
planeNode.eulerAngles.x = -.pi/2

//The Node Is Centered In The Anchor (0,0,0)
node.addChildNode(planeNode)

//6. Create AN SCNBox
let boxNode = SCNNode()
let boxGeometry = SCNBox(width: 0.1, height: 0.1, length: 0.1, chamferRadius: 0)

//7. Create A Different Colour For Each Face
let faceColours = [UIColor.red, UIColor.green, UIColor.blue, UIColor.cyan, UIColor.yellow, UIColor.gray]
var faceMaterials = [SCNMaterial]()

//8. Apply It To Each Face
for face in 0 ..< 5{
    let material = SCNMaterial()
    material.diffuse.contents = faceColours[face]
    faceMaterials.append(material)
}
boxGeometry.materials = faceMaterials
boxNode.geometry = boxGeometry

//9. Set The Boxes Position To Be Placed On The Plane (node.x + box.height)
boxNode.position = SCNVector3(0 , 0.05, 0)

//10. Add The Box To The Node
node.addChildNode(boxNode)

 }

如您所见，过程相当简单。因此，在您的情况下，您可能对上面使用此方法创建动态图像的转换函数更感兴趣：

init(CGImage, orientation: CGImagePropertyOrientation, physicalWidth: CGFloat)

Answer 2

解释 Human Interface Guidelines 用于 AR...图像检测 performance/accuracy 随着图像数量的增加而恶化。因此 API 没有硬性限制，但如果您尝试在当前检测集中放置超过 25 张图像，它将开始变得太 slow/inaccurate 以至于无法使用。

还有很多其他因素会影响 performance/accuracy，因此请将其视为准则，而非硬性限制。根据您运行应用程序所在位置的场景条件、您对 CPU 其他任务的压力程度、您的参考图像彼此之间的区别等，您可能会管理多于 25... 或少于 25 时开始出现检测问题。

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xcode

augmented-reality

ios

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