The figure illustrates the formula in geometric algebra for the
black vector which is the location in the image: it is a rescaled
version of the rejection of P by f. Drag the endpoint
of P or f, or the carrier of f, to study dependencies.
Since the whole construction has been defined in the plane of f
and P, it is not limited to 2 dimensions: the same construction
holds, with precisely the same formulas, for any point in 3-D (or even
n-D!).
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