We have developed an imaging simulation package for ALMA within the GILDAS software environment. The simulation takes into account most of the possible sources of errors affecting image quality: array configuration, pointing errors, tracking errors, atmospheric phase, gain calibration errors, primary beam errors, and thermal noise as well as the effects of observing strategies used to calibrate the zero order effects. Particular care has been taken to optimize for speed, since the evaluation of the imaging quality requires a large number of simulations. To do this, approximate, but sufficiently accurate solutions have been implemented rather than using the exact, but slower method.
The simulation package is driven by a simple GUI interface, on top of a command line interface. This system permits easy use by occasional users, as well as simple setup for large series of simulations. Example of simulation results are given, and the importance of chosen modeling methods are discussed.