At the department of IR-systems at the Swedish Defence Research Agency (FOI) the commercial software SensorVisionTM from MultiGen-Paradigm Incorporated is used for simulations of IR scenes. It is always desirable to increase the accuracy in the IR scene simulations. RadThermTM is a commercial software from ThermoAnalytics Incorporated which is suitable for very thorough temperature calculations of single objects. The two main advantages with RadThermTM, as compared to SensorVisionTM, are its capability to perform heat transfer calculations in three dimensions and the possibility to include internal heat sources in an object. This makes it very suitable for thermal calculations on, for instance, vehicles. Possibilities to import temperatures to SensorVisionTM from an external source have been investigated and the different ways of retrieving output-data from RadThermTM evaluated. A program has been constructed in Visual C++ which uses data from a RadThermTM simulation to set temperatures on a single object in real-time in SensorVisionTM.