I know rosenbergi is now known from the NT... We saw lots of Gynacantha on our trip and all looked like this. Slimmer abdomen than shown for rosenbergi in the guide. Appendages match dobsoni and the abdomen pattern matches. Although rosenbergi and dobsoni are similar I believe that abdomen pattern will differ enough to enable identification in the future.
Amazing dragonfly. In overcast weather, its tail gave the appearance of emanating its own light, like a lantern. It kept patrolling continuously while we observed for 10 minutes, even in light rain. These poor shots were for the best I could manage in the conditions - suitable for ID verification and record purposes only (there are much better photos on this platform).