I have now completed a mosaic project to cover the area of NIMT and ECMT that is within the bounds of Horotiu, Hamilton (Frankton) and Claudelands. These are the main areas of interest that I will be mapping at some future time (unscheduled at present) with NZ Rail Maps.
Whilst the mosaic is now complete with just over 100 layers on a canvas of 96000x93600 pixels (8,985,600,000 pixels, or 9 gigapixels), as noted in my previous post, much of the canvas is unoccupied because of the L shaped aspect of the rail corridor section covered.
At present for actual mapping I am still working on Dunedin and I do not know if any work will be done on the NIMT for some time as there are a number of areas being worked on. The idea at the moment has simply been to put the mosaics together quickly to see that it can be done a lot more smoothly and rapidly than the Dunedin urban mosaic project which has taken weeks to complete. This has been greately sped up by being able to use a linear corridor project rather than the segmented model used for Dunedin, one of the principal drawbacks of which is the need to duplicate overlapping layers between segments.
However another factor in Dunedin has been the significant number of layer eras sourced and incorporated into the project. This has not been done with the Hamilton project. Most of the historical imagery is from a single generation for most areas. The main exception is the ECMT section from Hamilton to Claudelands which incorporates three generations: 1953, 1961 and 1975. This is because of the major changes when the railway between Hamilton and Claudelands was undergrounded in the early 1960s and the change upon the urban landscape that was produced. There is also a 1966 image of Frankton Junction which shows the locomotive depot that was gone by the 1970s along with some other features in part of the yard.
In the Te Rapa mosaic project we have a corridor of 10 km roughly in length, which because of its shape uses the canvas inefficiently, yet we also have 100 layers and a file size of 18 GB. The clear implication from this is that there is no inherent resource usage efficiency from a segmented model as opposed to a linear model and therefore the linear model with its clear speed advantages is what will be preferred in future. As soon as the Te Rapa project is completed I intend to start on mosaic projects for Christchurch, which is at a higher priority for actual mapping, and integrate several sets of mosaics each for around 10 km of the urban rail corridors, which are currently implemented in small projects covering a km or two each.
The Te Rapa imagery dates from 1972 and I have since discovered there is some more available from the 1980s. However at the moment I am not intending to add any more generations to Te Rapa. Multiple generations are a feature of Christchurch and Dunedin mosaic projects at present because of a greater personal interest in this level of detail, which is not going to be the case across all mosaic projects, so that is essentially the difference in this case, because I simply do not have the time to delve into all of the historical details at every location at present.
The images below are from an album on the NZ Rail Maps page. Visit that page to see more information about them.
Hotoriu freezing works.
Te Rapa Air Force Base.
Main Te Rapa yard with hump to the far right.
Te Rapa loco depot 1972.
Frankton Junction. Was never a triangle.
Frankton passenger station.
Frankton Loco Depot 1966.
Hamilton Railway Station
Commencement of lowering works in Hamilton 1961. Bridge under construction at right.