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Naive Triangulation

    |    / \    |
    |   /   \   |
----+-x1-   -x2-+----  <-- image planes
   f| /       \f|
    |/         \|
----C1-----------C2---------> X
           b

C1 is the 1st camera center, located at the origin of the coordinate system XYZ (Y is sticks out of the screen). C2 is the 2nd camera center, located at (b,0,0). Pinhole cameras are assumed with focal distance f. Consider a 3d point X=(X,Y,Z) s.t. its projections onto the 1st and the 2nd image planes are given by x1=(u1,v1) and x2=(u2',v2') respectively (coords are given relative to the image planes).

u2'= u2-b => u2 = u2'+b

Triangle similarity gives: b/(u2-u1) = Z/(Z-f) bZ-bf = Zu2-Zu1 = Z(u2'+b)-Zu1 = Zu2'+Zb-Zu1 -bf = Zu2'-Zu1 Z = bf/(u1-u2)