Otago Central Railway [15]: Cromwell Gorge

So I haven’t made a lot of progress since the last post but work is coming along on finishing the gorge where a lot of the old railway route is under the shoreline or the lake from the hydropower development of the 1980s. As far as I know this situation is unique in New Zealand – most of our hydro developments haven’t gone anywhere near a railway line, although we know that the PWD used narrow gauge lines with their Hudswell Clarke diesel shunters and other locos to build some major civil engineering projects like the Waitaki Dam and some of the early Upper Waitaki projects at Tekapo and Pukaki.
Tekapo “A” power station construction in 1947 showing the narrow gauge tracks around part of the site.
So that has nothing much to do with the Cromwell Gorge but let’s get back onto that now. The aerial photos I got from LINZ, that date from the 1960s, are not geo referenced. In Google Earth it’s relatively easy to overlay them as images by changing the transparency and then lining them up with existing features. However it is never easy because both the new and existing imagery is very difficult to avoid optical distortions in – so this is rough at best. The same is true of the wizard that is provided in Qgis to achieve the same end (by matching up point coordinates) – which in my case had the added difficulty that there was some sort of mismatch because what I had lined up in the wizard didn’t match at all when the modified image was generated.
So I have simply had to realign things by hand and will also have to post a disclaimer that the result is not guaranteed to be accurate, for a number of reasons. All the same, it is going to be a good series of maps. Google Earth was the method of choice for a long time simply tracing features off their satellite maps and importing them to my maps. Google has always panned this being done for commercial reasons, presumably to prevent Google Maps competitors from copying stuff. It’s been the case for some time that there is considerable doubt whether my project could be considered non-commercial since the maps may well end up being sold for a tiny profit just to cover some costs, or someone else could resell them under the CC terms. Because of this I am now using the high quality modern Linz georeferenced imagery of the entire country that I can download and import directly into Qgis, and that is being used to draw all of the new maps. It is what I am using to check the old aerial photographs against to get the alignments worked out.
At the moment I am working on the section between Cromwell going around the Brewery Creek area (where the route is out of the water) and down to Gibraltar Rock where the cutting that the railway and road used to run through side by side is still intact. All this of course will be documented and written up in the article. I have settled just for finishing the Cromwell Gorge section to start off with, and then I can leave the large amount of work needed to finish the rest of the maps (a number of yard layouts are still to be drawn) for maybe next holidays when I will start working on the second article.

UPDATE: Realigning has got almost to Waenga which is about a quarter of the total length of the railway line through the gorge. With the marking of milepegs and other work to be done, I estimate it should take until the end of this week to complete the Gorge maps, allowing me to start writing next week hopefully.