SIMply – an open source image simulation tool supporting the research and development of spaceborne imaging systems

Image simulation entails the generation of synthetic image data using detailed models of cameras and scenes, and light’s interaction with them. When these models are defined by physical rules (referred to as physically based rendering – PBR), images can be generated with very high levels of physical accuracy. Such images can be used to test camera capabilities and characterise the performance of image analysis algorithms, making PBR a valuable tool for the development and testing of planetary science and other spaceborne cameras.

The camera hardware and data processing/analysis pipelines of planetary science cameras require rigorous testing and validation to ensure correct performance. Given that spaceborne cameras will commonly operate at locations that have rarely or never been visited before, there is often minimal relevant existing image data available for use in camera development, particularly for novel imaging systems. Image simulation can support camera development in these cases by modelling camera performance and providing data on which to test processing or analysis techniques. Image simulation is fast, low cost and flexible, with all aspects of a simulated imaging scenario being controllable, from scene appearance to camera response. It can be used to predict the range of observation conditions (e.g. radiance distribution, shadowing) that a camera will encounter, to visualise the nature of a particular camera’s image data, or to test algorithm performance (such as stereo reconstruction accuracy).

SIMply (Python Image Simulator for Planetary Exploration) is an open source physically-based image simulator designed to make the benefits of image simulation widely available to researchers and engineers working on spaceborne imaging systems [1,2]. SIMply is designed with an emphasis on simplicity and accessibility – being free, open source, written in pure Python and compatible with standard computing setups. SIMply can be used to set up and render complex scenes with only a few lines of Python code, and the physical accuracy of its rendering pipeline is validated [1]. SIMply is built to be inherently flexible and extendable, making customisation such as bespoke cameras or surface reflectance models easy to implement. SIMply is therefore designed to be sustainable, enabling it to continually gain functionality over time in response to community needs.

SIMply can be used to simulate physically accurate images of a wide variety of planetary exploration scenes (from planets and moons to small bodies and artificial objects, see Fig 1). Rendering is performed using ray tracing and physical models of surface shape, spectral reflectance, spectral camera response, and imaging geometry. SIMply is currently supporting a variety of planetary surface imaging research. The tool can be accessed and downloaded at https://github.com/gbrydon/SIMply.

Fig 1. Various SIMply simulations. A) Simulated orbital image of Mars’ surface. B) Simulated colour image of the Moon with chromatic aberration. C) Simulated long-range image of comet 67P and background stars – with incorporation of external dust radiance model. D) Simulated image of a spacecraft during rendezvous and proximity operations. E) Side-by-side comparison of real (left) and simulated (right) Rosetta OSIRIS WAC images of comet 67P’s nucleus.

References

[1] Brydon G., Image simulation for camera development - Python Image Simulator for Planetary Exploration (SIMply). Space Science & Technology, 2025; [2] SIMply tool, https://github.com/gbrydon/SIMply;