  We study the photon detection efficiency and position resolution of the
electromagnetic calorimeter (EMC) of the BESIII detector. The control samples
of the initial-state-radiation (ISR) process of $e^+e^-\rightarrow \gamma
\mu^+\mu^-$ at $J/\psi$ and $\psi(3770)$ resonances are used for the
calibration of the photon cluster shapes and photon detection efficiency study.
The photon detection efficiency is defined as the fraction of predicted photon,
determined by performing a kinematic fit with the four momenta of two charged
tracks only, matched with the actual photons in the EMC. The spatial resolution
of the EMC is studied in polar ($\theta$) and azimuthal ($\phi$) angle
directions in a cylindrical coordinate system centered at the interaction
point, with z-axis along the beam direction.
