• LineRatioFit is used to determine H volume density \(n\) and radiation field \(F_{UV}\) from your observations. Observations can be single pixel or maps and are represented in pdrtpy as Measurements.
• LineRatioPlot plots the results of LineRatioFit. It can plot maps of fit results, observations with errors on top of models, chi-square and confidence intervals and more.
• H2ExcitationFit is a tool for fitting temperature, column density, and ortho-to-para ratio in H₂ excitation diagrams. A two temperature model is assumed, and the fit will find warm and cold gas temperatures and column densities, and optionally ortho-to-para ratio. The base class ExcitationFit can be used to create a tool to fit a different molecule.
• ExcitationPlot creates excitation diagrams using the results of H2ExcitationFit. It can plot the observed excitation diagram with or without fit results, and allows averaging over user-given spatial areas.
• ModelPlot is a tool for exploring sets of models. It can plot individual intensity or ratio models, phase-space diagrams, and optionally overlay observations. Units are seamlessly transformed, so you can plot in Habing units, Draine units, or any conformable quantity.

The best way to learn how to use pdrtpy is to install it and work through the notebooks. We suggest you do the notebooks in this order:

• PDRT_Example_Measurements.ipynb
• PDRT_Example_ModelSets.ipynb
• PDRT_Example_Model_Plotting.ipynb
• PDRT_Example_Find_n_G0_Single_Pixel.ipynb
• PDRT_Example_Make_n_G0_maps.ipynb
• PDRT_Example_H2_Excitation.ipynb

The "classic" PDRT website and tools have now been shut down. We will not update the models or code there. We urge you to transition to pdrtpy with alacrity as it already has better functionality and is where all development will be concentrated.