Monday, 8 April 2019

MSL Dunedin-Mosgiel [0D]: Intro 4

Dunedin-Mosgiel map mosaics have been completed with the addition of historical maps of the Mosgiel area. After this was done, the entire set of mosaics was reviewed and it was found three more pieces needed to be added in Dunedin. These were near the Water of Leith railway bridge where there were gaps in both 1972 and 1942 coverage, and a 1942 map of the route of the Dunedin Peninsula & Ocean Beach Railway line (not the current OBR line).

Mosgiel includes the first part of the Outram line which was a siding to the woollen mill. In 1966 when the aerial photos were taken this siding was still in use. This seems to have ceased by the early 1970s, by 1975 the siding had been lifted back to the first bridge, which was on the first curve where it turned 90 degrees from the MSL to run up into Mosgiel.

I did consider putting the Outram Branch into this project using the 1942 aerial photos but decided to leave that for a separate project that will cover the whole branch sometime in the future but it will not show much detail of the stations as the 1942 aerial images are not particularly sharp.

I previously had Caversham in 1942 coverage (and have tiles for it that I produced from an earlier version of the project) but decided to remove this because sufficient pre-motorway coverage is available around Caversham from the 1970s. 1942 coverage generally is not sharp enough to be of much use and for the maps has been limited to a few select areas of specific interest. These are Dunedin yard, the routes of the DPOBR Walton Park and Fernhill branch lines, and Wingatui which had industrial sidings that were gone by the 1970s. In most cases these images are too blurry to have much usefulness for mapping. For all other areas, the earliest coverage used (only in some areas) is from the 1960s. The main interest for having coverage of any areas before the 1970s is, as alluded to above, the desire to show what Dunedin looked like before the southern motorway was put through, all along the rail corridor, which in particular around Caversham was diverted and singled.

So far the areas I have extracted tiles for are:
  • Dunedin 1942 (incomplete)
  • Dunedin 1972
  • Kensington 1972
  • Caversham 1979
South of Dunedin most stations have changed little over the years and there is no real need for coverage before 1960. Although it is hard to find coverage at a good resolution pre-motorway between Kensington and Green Island, a combination of 1978 and 1960 surveys that have been located will give a reasonable view of the area. The motorway works started at the south end of Dunedin (Green Island etc) in the early 1970s and at the middle (Kensington) in the late 1970s and finding aerial coverage that is of good enough quality is hard as 1942 is not very sharp. It's only been included of Dunedin station for historical interest of a major yard in the middle of the city.

Most of the surveys used are from the following collections:
  • 1942 general aerial imagery of Dunedin. As much of NZ is covered by these series they were probably intended for military purposes. Survey numbers are in the 200 range.
  • 1960 Dunedin Milton Motorway. Series A is relevant to Dunedin - survey no. 1299
  • 1966 State Highway 87 District 17 - Mosgiel. This is survey no. 1915 which happens to cover some stations up the Otago Central Railway (as SH 87 runs from Mosgiel to Kyeburn where it joins the Pigroot - SH 85, and thus close to the OCR from Sutton to Kokonga).
  • Most of the other surveys were done specifically for NZR, for the various stations in Dunedin (Caversham and Abbotsford did not have these surveys done). There is a large survey done for NZR in 1978, no. 5248, which covers the entire MSL from Palmerston to Mosgiel. I am downloading every image in it for future reference because it means I can map every station in that section and that might be the next big set of map mosaics done. But that will depend on how long it takes to assemble such mosaics. 
Tomorrow therefore I will have the ability to start extracting the tiles from the mosaics to be mapping all across the area. The mosaics out of interest were all in one file, which reached a peak size of 53 GiB before it got too difficult for my computer to handle (running out of SSD swap space which slows Gimp down a lot swapping to the hard disk and seems to make it more unstable). At that point it was split into two files.