  Context: Optical interferometry is a powerful tool for observing the
intensity structure and angular diameter of stars. When combined with
spectroscopy and/or spectrophotometry, interferometry provides a powerful
constraint for model stellar atmospheres. Aims: The purpose of this work is to
test the robustness of the spherically symmetric version of the Atlas stellar
atmosphere program, SAtlas, using interferometric and spectrophotometric
observations. Methods: Cubes (three dimensional grids) of model stellar
atmospheres, with dimensions of luminosity, mass, and radius, are computed to
fit observations for three evolved giant stars, \psi Phoenicis, \gamma
Sagittae, and \alpha Ceti. The best-fit parameters are compared with previous
results. Results: The best-fit angular diameters and values of \chi^2 are
consistent with predictions using Phoenix and plane-parallel Atlas models. The
predicted effective temperatures, using SAtlas, are about 100 to 200 K lower,
and the predicted luminosities are also lower due to the differences in
effective temperatures. Conclusions: It is shown that the SAtlas program is a
robust tool for computing models of extended stellar atmospheres that are
consistent with observations. The best-fit parameters are consistent with
predictions using Phoenix models, and the fit to the interferometric data for
\psi Phe differs slightly, although both agree within the uncertainty of the
interferometric observations.
