Transition radiation is produced when an electron moving at constant speed
crosses the boundary separating two media with different optical properties
. We propose an alternative description of this phenomenon, based on an int
egral representation of the electromagnetic held and show that the approach
gives known results for a hat surface. Compared to previously published me
thods, based either on the reciprocity theorem in electromagnetism or on a
four-dimensional Fourier representation of the field generated by the movin
g electron, this method has the advantage that it can be applied to general
boundary geometries.