There are 3 things that would help with calculating some of the ideal gas equations that KSP uses to model it's atmospheres

The first is the molecular weight of that gas that makes up a given atmosphere
This value is needed to calculate the density of an atmosphere
For kerbin this value should be about 28.9644 g/mol and for duna it should be about 42 g/mol

The second is the called the adiabatic index or heat capacity ratio depending on source
This value is needed to calculate the speed of sound in at a given atmospheric temperature
For kerbin this value should be about 1.4 and duna it should be about 1.2

Also if possible the ability to get the temperature of a given position would be extremely useful for atmospheric calculations if not as essential as the first 2

The reasons theses values are needed is currently they are only available though an external source like the KSP forums or wiki and for modded star systems like galileo planet pack the bodies might have completely different atmospheres from stock and might not be easy to find the information on there atmospheres