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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 $RC+t=0$. HenceThis follows by applying the inverse rotation to the zero camera-space position.^[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.

In an ideal camera model, the principal point is the intersection of the optical axis with the image plane, expressed in image pixel coordinates $(c_x,c_y)$. It supplies the coordinate offset in perspective projection. For a scene point $(X,Y,Z)$ expressed relative to the camera, the model iswhere $f_x,f_y$ are focal lengths in pixel units. Thus the principal point belongs to the camera's internal geometry; the camera's position and orientation in the world are separate parameters.^[ref]

For $f_x=800$, $c_x=320$, $X=0.1$ metres and $Z=2$ metres, the horizontal coordinate is $u=360$ pixels. A point on the optical axis instead has $X=Y=0$ and projects to $(c_x,c_y)$. The principal point is often near the image center, but camera calibration estimates it rather than establishing that it must be exactly centered. Cropping an image also changes the principal point's coordinate values: removing 20 columns from the left changes $c_x=320$ to $300$, without physically moving the optical axis.