imSim: The GalSim based Rubin Observatory image simulation package

imSim is a software package that simulates the Rubin Observatory and LSST survey. It produces simulated images from the 3.25 Gigapixel camera which are suitable to be processed through the Rubin Data Management pipeline. imSim produced the simulated exposures used in the DESC DC2 data challenge, and is the basis for the DP0 Data Set used by the wider Rubin Science community. imSim is open source software and its development is overseen in the DESC.

This documentation covers installation, configuration, and usage instructions for the imSim program. It also includes descriptions of several of the models implemented by imSim.

The source code of imSim is hosted at https://github.com/LSSTDESC/imSim.

Contents

• Installation Instructions
  • Method 1: Using the cvmfs distribution
  • Method 2: Conda and the Stackvana package
  • Method 3: Using the pre-built imSim Docker image
  • Method 3: Building your own imSim Docker image
  • Testing your installation
• Using imSim
• The Config System
  • Input types
  • Image types
  • StampTypes
  • Output types
• Features Implemented in imSim
  • Sensor Effects
  • Sky Model
  • System Throughputs
  • Atmospheric PSF model
  • Optical model
  • Calibration Products
  • Detailed Description of Physical Effects Implemented in imSim
• Data formats of input and output files
• Understanding the LSST Camera
  • The Camera Layout
  • Specifying which sensors to simulate
• The Rubin Optical System
  • Controlling Optical Perturbations
  • Specifying FEA parameters
• Using the imSim module with other GalSim based Programs