kitti数据集相机投影矩阵 [英] kitti dataset camera projection matrix

问题描述

我正在查看kitti数据集，尤其是如何将世界点转换为图像坐标。我看了一下README，并在下面说，我需要先转换为相机坐标，然后再乘以投影矩阵。我有2个问题，来自非计算机视觉背景

I am looking at the kitti dataset and particularly how to convert a world point into the image coordinates. I looked at the README and it says below that I need to transform to camera coordinates first then multiply by the projection matrix. I have 2 questions, coming from a non computer vision background

1. 我查看了calib.txt中的数字，尤其是矩阵为3x4在最后一列中具有非零值。我一直以为这个矩阵 = K [I | 0] ，其中K是相机的固有矩阵。那么，为什么最后一列非零，这意味着什么呢？例如P2是

1. I looked at the numbers from calib.txt and in particular the matrix is 3x4 with non-zero values in the last column. I always thought this matrix = K[I|0], where K is the camera's intrinsic matrix. So, why is the last column non-zero and what does it mean? e.g P2 is

array([[7.070912e+02, 0.000000e+00, 6.018873e+02, 4.688783e+01],
       [0.000000e+00, 7.070912e+02, 1.831104e+02, 1.178601e-01],
       [0.000000e+00, 0.000000e+00, 1.000000e+00, 6.203223e-03]])

1. 将投影应用于[u，v，w]并将u，v除以w之后，这些值是相对于图像中心处的原点而言的还是原点在图片的左上方？

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自述文件：

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README:

calib.txt：摄像机的校准数据：P0 / P1是校正后的3x4
投影
矩阵。这里P0表示左摄像机，P1表示右摄像机
。 Tr将点从Velodyne坐标转换为
左校正的相机坐标系。为了将点x从
velodyne扫描仪映射到第i个图像平面中的点x，您必须像这样对
进行变换：

calib.txt: Calibration data for the cameras: P0/P1 are the 3x4 projection matrices after rectification. Here P0 denotes the left and P1 denotes the right camera. Tr transforms a point from velodyne coordinates into the left rectified camera coordinate system. In order to map a point X from the velodyne scanner to a point x in the i'th image plane, you thus have to transform it like:

  x = Pi * Tr * X

推荐答案

对于所有P矩阵（3x4），它们表示：

For all the P matrices (3x4), they represent:

P(i)rect = [[fu 0  cx  -fu*bx],
            [0  fv  cy -fv*by],
            [0   0   1  0]]

最后一列是基线，以米为单位参考相机0。您可以在最后一列中看到P0都为零，因为它是参考相机。

Last column are baselines in meters w.r.t. the reference camera 0. You can see the P0 has all zeros in the last column because it is the reference camera.

这篇文章有更多详细信息：
如何计算Kitti校准矩阵？

This post has more details: How Kitti calibration matrix was calculated?

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