We only have pictures of the caterpillars of less than 200 of the nearly 1300 named Australain Geometridae. I do not think the similarity to the photos we have of P. cognata is good enough to identify this specimen as that species. It would be really good if you could take this larva into protective custody and rear it to the adult moth to find out more surly what its species is. Meanwhile, it would be another clue if you could identify the plant on which it was feeding.