  Through synthetic observations of a hydrodynamical simulation of an evolving
star-forming region, we assess how the choice of observational techniques
affects the measurements of properties which trace star formation. Testing and
calibrating observational measurements requires synthetic observations which
are as realistic as possible. In this part of the paper series (Paper I), we
explore different techniques for how to map the distributions of densities and
temperatures from the particle-based simulations onto a Voronoi mesh suitable
for radiative transfer and consequently explore their accuracy. We further test
different ways to set up the radiative transfer in order to produce realistic
synthetic observations. We give a detailed description of all methods and
ultimately recommend techniques. We have found that the flux around 20 microns
is strongly overestimated when blindly coupling the dust radiative transfer
temperature with the hydrodynamical gas temperature. We find that when instead
assuming a constant background dust temperature in addition to the radiative
transfer heating, the recovered flux is consistent with actual observations. We
present around 5800 realistic synthetic observations for Spitzer and Herschel
bands, at different evolutionary time-steps, distances and orientations. In the
upcoming papers of this series (Paper II, Paper III and Paper IV), we will test
and calibrate measurements of the star-formation rate (SFR), gas mass and the
star-formation efficiency (SFE) using our realistic synthetic observations.
