Poeppel was not born to the outback - few were. He came into the world in Hamburg in 1839, the son of an architect, and emigrated with his family in 1849 to settle in South Australia. He trained as a mining surveyor and architect, worked in Victoria, and tried his luck briefly in New Zealand and Western Australia before joining the South Australian Lands Department in 1878. There he was handed one of the hardest jobs the young colonies had to offer: fixing the invisible lines that the map insisted ran through the centre of the continent, across country that had never been surveyed and that few colonists had ever crossed.

Poeppel's task was to give those lines a physical reality. He surveyed and marked two of the most remote boundary points in Australia. One was Poeppel Corner, where Queensland, South Australia and the Northern Territory converge among the parallel red dunes of the Simpson Desert. The other was Haddon Corner, the right-angle junction of the Queensland and South Australian borders to the southeast. These were not symbolic gestures. Pastoral leases, jurisdiction, and law all hinged on knowing exactly where one colony ended and the next began - and out here, with no rivers or ridges to follow, the only border was the one a surveyor could measure and peg into the ground himself.

The desert exacted a heavy price for its lines. During the Queensland-Northern Territory survey, pressing on from the 142-mile post, Poeppel fell ill with trachoma, the painful eye disease that haunted the dusty inland. He lost 13 kilograms and, in July 1885, was forced to abandon the work. His health never recovered. He eventually lost the sight in one eye - a cruel fate for a man whose entire profession depended on precise observation. The blindness that crept over him was, in a sense, the desert's final correction: the surveyor who measured the unmeasurable was undone by the very country he had charted.

Poeppel retired to Melbourne and died there in 1891, aged just 52. His error did not go uncorrected: the corner post was reset following a resurvey, and in 1884 the surveyor Lawrence Wells moved it to its proper position near the eastern bank of Lake Poeppel. But the name endured, and so did the story. Both Poeppel Corner and Haddon Corner are now listed on the Queensland Heritage Register, drawing four-wheel-drive travellers who make the difficult pilgrimage across the dunes to stand where three states touch. There is a quiet justice in it. Most monuments celebrate flawless triumphs. This one honours a man who did backbreaking, half-blind work in an impossible place - and whose famous mistake only makes the achievement more human.