Camera export is pretty straight forward these days. I use a script thats freely available on creative crash 'Maya to Nuke exporter', or just do a search for .chan export.
The only thing after that is re-setting the scale in terragen (when importing the .chan file), according to the unit difference between the two apps.
We usually work in cm in maya, so I just have to adjust the scale to meters in terragen, so multiply by 10.
Hope that helps.
Chris
