yes,
right, but if someone wanted to do this, those are preprocessor macros that could be easily exposed/overridden via CLI flags - I mean, it's the equivalent of running sed against the SG/TG source trees to replace any references to the corresponding macros to a std::map<std::string, double> lookup table that gets populated during initialization (i.e. values being defaulted to what they are now).
Alternatively, we could have a planet.xml file using the existing propertyList xml file dialect and let people create/provide such files for whatever they want to do.
Replacing those constants is relatively straightforward compared to all the data manipulation and DEM processing that TG can already handle, and I guess there are quite a few other hard-coded assumptions in various parts of SG/FG and TG, too
Then again, this is a long-standing idea, and even some of the original TG authors (think Curt) were tossing with such ideas - to see for yourself, search the archives for "
TerraGear mars" or "
TerraGear planets"
The main reference thread dating back to early 2002:
Getting settled in my new "home" / Mars Scenery (look for answers from Curt, Jon, David Megginson
So preparing SG/TG to make such things possible would definitely be a worthwhile thing according to quite a number of discussions in the archives (many of which being inspired by X-Plane's Mars mode) - and with JSBSim already supporting custom atmosphere models, and given the recent revamped interest supporting spaceflight, why not ?
It's seems we're already well on our way ...