= Epipolar geometry
{wiki}
<Epipolar geometry> describes the projective relationship between two <camera> views. A scene point away from the <camera baseline> and the two <camera centers> determine an <epipolar plane>. Its intersections with the image planes are corresponding <epipolar lines>. Knowing one image point therefore constrains its partner to a line rather than the whole second image.<Epipolar Geometry in the OpenCV-Python tutorials>[Basic Concepts, two-camera plane and epipolar constraint]{ref}
With image points in <homogeneous coordinates>, a <fundamental matrix (computer vision)> $F$ expresses the constraint
$$
q_R^{\mathsf T}Fq_L=0.
$$
For an ideal horizontally rectified pair this reduces to equality of image-row coordinates, while horizontal displacement remains free and carries <stereo disparity>. A line constraint does not determine depth: many scene points along one viewing ray satisfy the geometry. Correct <stereo correspondence> selects a partner, and <camera calibration> then supports metric <stereoscopic triangulation>.
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