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The theoretical understanding of the spin-orbit coupling (SOC) effects at LaAlO/SrTiO interfaces and SrTiO surfaces is still in its infancy. We perform first-principles density-functional-theory calculations and derive from these a simple tight-binding Hamiltonian, through a Wannier function projection and group theoretical analysis. We find striking differences to the standard Rashba theory for spin-orbit coupling in semiconductor heterostructures due to multiorbital effects: By far the biggest SOC effect is at the crossing point of the and (or ) orbitals, and around the point a Rashba spin splitting with a cubic dependence on the wave vector is possible.