(Townhall-monument on nexusmods, main.rdm, there's another 10 rdm files.)

There is an interesting model converter here. (Didn't check it so far but seems to be capable of obj2rdm, too.)

(Interesting to see that no one around here cares for Anno 1800 models - so I'm really glad that I didn't invest much time on this...)

I added the Anno 2070 *.RDM loader module to the 3D Object Converter on August 12, 2015.