Before we set out to actually find the motion between two cameras, let's examine the inputs and the tools we have at hand to perform this operation. First, we have two images of the same scene from (hopefully not extremely) different positions in space. This is a powerful asset, and we will make sure that we use it. As for tools, we should take a look at mathematical objects that impose constraints over our images, cameras, and the scene.
Two very useful mathematical objects are the fundamental matrix (denoted by
F) and the essential matrix (denoted by
E), which impose a constraint over corresponding 2D points in two images of the scene. They are mostly similar, except that the essential matrix is assuming usage of calibrated cameras; this is the case for us, so we will choose it. OpenCV allows us to find the fundamental matrix via the
findFundamentalMat function and the essential matrix via the
findEssentialMatrix function. Finding the essential...