So I have been taking a look at the Cromwell Gorge aerial data again after discovering my maps didn't line up with the 0.4 metre aerial photos from LINZ. Well it turns out that I completely misaligned the aerials when I originally checked them against the original maps. In fact it was done very quickly and roughly, enough to create more than a few errors.
Qgis does a great job with georeferenced images of loading them in the right place. However with images that are not georeferenced you have to use a built in wizard. It would make more sense to me to be using a transparency overlay to map the points directly, and that's because their wizard couldn't make things line up when I tried it twice.
The very first attempt to get things in line properly has put most of the Cromwell yard under dirt at the toe of the highway, rather than in the water. For years people have speculated about the supposed underwater finds to be had. Whilst some may exist, the statement by D&E that no traces remain west of Clyde is probably closer to the truth of the matter. The fact they have stated for example that the Leaning Rock bridge was buried under a pile of rock prior to filling the lake, and that bridge being built of concrete was one of the very few that were not actually removed outright. The aerial photo set from 1992 shows really very little trace of the railway by that stage as a lot of earthworks had occurred.
My new understanding of where the line ran due to adjusting the position of the aerial photos puts a lot more of it onto dry land, but not where it can be traced as a lot of this has been contoured by machinery destroying any formation traces. Even in places where a formation can be discerned like at Brewery Creek near Cromwell or Gibraltar Rock where the original rock cutting is still well above the water line, people who have had a look report there are no traces of anything of a railway nature to be found today.
It shouldn't take long to get the images realigned and then the proper lineup put in for the actual road, railway and other features going through the Gorge. Finishing the maps is all important because then I can start writing my article.
