将3D世界(arcore锚点/姿势)转换为其相应的2D屏幕坐标 [英] Convert 3D world (arcore anchor/pose) to its corresponding 2D screen coordinates

问题描述

我正在努力实现这种转变.给定arcore中的锚点姿势，如何在屏幕上获取其对应的2D坐标?

I'm struggling to get this transformation. Given an anchor Pose in arcore how can I obtain its corresponding 2D coordinates in the screen?

推荐答案

最后，经过几天的调查并从其他资源中获取了信息，我才能够使它工作.以下是一个代码片段(基于arcore示例Java应用)，可以将世界坐标(Arcore中的姿势)转换为2D屏幕坐标:

Finally, after some days of investigation and getting the information from different resources I was able to get this working. Following is a code snippet (based on the arcore sample java app) to convert from World coordinates (Pose in arcore) to 2D screen coordinates:

首先，我们需要计算要从世界转换的矩阵->屏幕:

First we need to calculate the matrix to transform from world --> screen:

  public float[] calculateWorld2CameraMatrix(float[] modelmtx, float[] viewmtx, float[] prjmtx) {

    float scaleFactor = 1.0f;
    float[] scaleMatrix = new float[16];
    float[] modelXscale = new float[16];
    float[] viewXmodelXscale = new float[16];
    float[] world2screenMatrix = new float[16];

    Matrix.setIdentityM(scaleMatrix, 0);
    scaleMatrix[0] = scaleFactor;
    scaleMatrix[5] = scaleFactor;
    scaleMatrix[10] = scaleFactor;

    Matrix.multiplyMM(modelXscale, 0, modelmtx, 0, scaleMatrix, 0);
    Matrix.multiplyMM(viewXmodelXscale, 0, viewmtx, 0, modelXscale, 0);
    Matrix.multiplyMM(world2screenMatrix, 0, prjmtx, 0, viewXmodelXscale, 0);

    return world2screenMatrix;

}

一旦有了这个矩阵，就可以将点从3D世界投影到2D，但是在投影过程中，我们必须从NDC坐标转换为屏幕.以下是执行此转换的方法:

Once we have this matrix, then we can project points from 3D world to 2D, but during this projection we have to convert from NDC coordinates to screen. Following is the method that performs this conversion:

  double[] world2Screen(int screenWidth, int screenHeight, float[] world2cameraMatrix)
  {
    float[] origin = {0f, 0f, 0f, 1f};
    float[] ndcCoord = new float[4];
    Matrix.multiplyMV(ndcCoord, 0,  world2cameraMatrix, 0,  origin, 0);

    ndcCoord[0] = ndcCoord[0]/ndcCoord[3];
    ndcCoord[1] = ndcCoord[1]/ndcCoord[3];

    double[] pos_2d = new double[]{0,0};
    pos_2d[0] = screenWidth  * ((ndcCoord[0] + 1.0)/2.0);
    pos_2d[1] = screenHeight * (( 1.0 - ndcCoord[1])/2.0);

    return pos_2d;
  }

最后，是一个简单的用法示例:

Finally, a simple example of usage:

        DisplayMetrics displayMetrics = new DisplayMetrics();
        getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
        int height = displayMetrics.heightPixels;
        int width = displayMetrics.widthPixels;

        // Get projection matrix.
        float[] projmtx = new float[16];
        camera.getProjectionMatrix(projmtx, 0, 0.1f, 100.0f);

        // Get camera matrix and draw.
        float[] viewmtx = new float[16];
        camera.getViewMatrix(viewmtx, 0);

        float[] anchorMatrix = new float[16];
        anchor.getPose().toMatrix(anchorMatrix, 0);
        float[] world2screenMatrix =    
        virtualObject.calculateWorld2CameraMatrix(anchorMatrix, viewmtx, projmtx);
        double[] anchor_2d =  world2Screen(width, height, world2screenMatrix);

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