Well this series of posts  is turning into a series about Cromwell-Alexandra really. There is still a surprising amount of work needed just to finish this first section of the maps as they correspond to the article series. It is being pushed ahead as fast as I can go but I have to admit it is a lot of work and has taken longer than expected. I have been surprised at the number of issues to be resolved. Fortunately it is coming together but it would not surprise me if it takes the rest of this year to complete those maps, which originally, optimistically, I had planned would all be completed with the articles.
The work still to be done is a mixture of aerial photos and map data. If I had stuck to just plain maps (diagrams as I now call them) then everything would be completed by now. Bringing in the aerial photos has added complexity and time delays, but I would not have it any other way now, because having the aerial data makes it possible to draw the track and structure layout in a yard accurately and other historical information can be viewed as well. In other words, the maps have gained immeasurably through having the aerial photo background available. The detail there means we don’t need to use Google Earth as an alternative or anything to do with Google Earth at all, with all its limitations and complexities of its own.
Anyhow, the past few days have been focused on collecting all of the aerial photos for the entire Otago Central Railway from Wingatui to Cromwell. It looks like this data set will be 2-3 GB in total, which is a far cry from the total space taken up for all the aerial photo layers I have, by only copying the images corresponding to the actual corridor back to mainpc. Right now I am working on Wingatui-Middlemarch as the aerials are broken into four groups corresponding to the article parts (Wingatui-Middlemarch and Middlemarch-Ranfurly are two distinct aerial photo sections whilst they were both covered in one article part in the NZRO series).
This gives me an idea of how much work I need to do to get all the aerials fixed up as there are several instances where there are overlap problems. Basically there are in each case two different aerial series that overlap, usually from different years, sometimes from different resolutions, and for some reason the chosen boundary is not along the edge of the aerial tile, so extra black bits are added. If the black pieces are cut off in Gimp then I can actually align the tiles so there is no unsightly gap, and then render out custom versions of each tile to go back into the maps. I expect to start doing this in the Omakau-Cromwell section today, but I need to use the full map in Qgis to guide this, and so getting the map fully there with all the aerial photos will enable this work of editing specific tiles to get underway properly. Doing this means all the maps can use the higher resolution imagery of 0.4 metres minimum, or in some cases 0.125 metres (all of Middlemarch-Wingatui section) instead of the 0.75 metre stuff I used during some of the earlier mapping stages.