The regions surrounding an accelerating charge where field energies are calculated. Here is the particle position when it started accelerating, and . Thus there is just a Lorentz contracted Coulomb field in the region , while there exist both generalized Coulomb and radiation fields in region . The innermost ellipse is the cross-section through the Lorentz contracted sphere (i.e., it is an ellipsoid) centered at the current position of the charge and withradius (not shown on this diagram) in the rest frame of the particle. Hence the charge has a finite radius that is necessary to provide a cut-off for the energy integrals to keep them finite. Region where Eriksen and Grøn localized the Schott energy, lies between this ellipsoid and a retarded sphere tangential to the ellipsoid. Furthermore, is the particle position at time and . The relationship between and is given in (2.8).
