= Camera center
{title2=$C=-R^{\mathsf T}t$}
The <camera center> is the center of projection in an ideal perspective <camera> model: the common origin of its viewing rays. It is a point in scene space, distinct from a <principal point>, which is an image-plane coordinate. Two distinct <camera centers> define the <camera baseline> used by <stereoscopy>.
For the calibrated <perspective projection> model $q\sim K(RP+t)$, where $R$ is a <rotation matrix>, the <camera center> $C$ satisfies $RC+t=0$. Hence
$$
C=-R^{\mathsf T}t.
$$
This follows by applying the inverse rotation to the zero camera-space position.<Camera Calibration and 3D Reconstruction by OpenCV>[Detailed Description, world-to-camera transform and projection equations]{ref} For $R=I$ and $t=(-0.1,0,0)$ metres, $C=(0.1,0,0)$ metres: the translation parameter is not directly the world-space <camera center>. Rotating about that center changes viewing directions without creating a new triangulation baseline.
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