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ios - ARCamera.projectPoint 快速实现

问题描述

我正在尝试使用相机中的 projectionMatrix 和 viewMatrix 来实现 ARCamera.projectPoint 函数。

将创建这样的东西：

let position = simd_float3(x: 1, y: 2, z: 3)
let position4 = simd_float4(x: position.x, y: position.y, z: position.z, w: 1)

let projectionMatrix = frame.camera.projectionMatrix(for: .landscapeRight, viewportSize: frame.camera.imageResolution, zNear: 0.001, zFar: 1000.0)
let viewMatrix = frame.camera.viewMatrix(for: .landscapeRight)

let projection = position4 * projectionMatrix * viewMatrix
let arkitProjection = frame.camera.projectPoint(position, orientation: .landscapeRight, viewportSize: frame.camera.imageResolution)

assert(projection.x == Float(arkitProjection.x))
assert(projection.y == Float(arkitProjection.y))

但我不知道如何正确实现它。希望对你有所帮助。

标签： iosswiftrenderlinear-algebraarkit

解决方案

你很亲近！你所拥有的projection实际上是一个“剪辑空间”位置（还要注意我固定了矩阵乘法的顺序）。然后，您需要使用“透视除法”将其转换为“标准化设备坐标”（xyz 维度的坐标从 -1 到 +1）。最后，您需要根据图像大小将其线性映射到图像中的位置。

let position = simd_float3(x: 1, y: 2, z: 3)
let position4 = simd_float4(x: position.x, y: position.y, z: position.z, w: 1)

let projectionMatrix = frame.camera.projectionMatrix(for: .landscapeRight, viewportSize: frame.camera.imageResolution, zNear: 0.001, zFar: 1000.0)
let viewMatrix = frame.camera.viewMatrix(for: .landscapeRight)

let clipSpacePosition = projectionMatrix * viewMatrix * position4
let normalizedDeviceCoordinate = clipSpacePosition / clipSpacePosition.w
let projection = CGPoint(
    x: (CGFloat(normalizedDeviceCoordinate.x) + 1) * (frame.camera.imageResolution.width / CGFloat(2)),
    y: ((-CGFloat(normalizedDeviceCoordinate.y) + 1)) * (frame.camera.imageResolution.height / CGFloat(2))
)

let arkitProjection = frame.camera.projectPoint(position, orientation: .landscapeRight, viewportSize: frame.camera.imageResolution)

assert(abs(projection.x - arkitProjection.x) < 0.01)
assert(abs(projection.y - arkitProjection.y) < 0.01)

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