The structural properties of epitaxial InGaAs grown (001) oriented GaAs have been studied by soft x-ray photoelectron diffraction. Polar and azimuthal scans at the Ga 3d, As 3d and In 4d core levels have been recorded to investigate the effects of strain on the epitaxial layer. The experimental results are compared with single scattering cluster calculations and a good agreement is obtained between theory and experiment showing that the lattice expands in the growth direction as predicted by the elastic theory. The influence of GaAs surface reconstruction (2 x 4) and (4 x 2) has also been studied and shows that the reconstruction does not induce significant changes in the photoelectron diffraction spectra.