Wednesday, 12 December 2018

Palmerston North Gisborne Line [0A]: PNGL maps revision project commencement

It's been four years since I published the maps for this section (Volume 8 in the old volume numbering scheme) and having road tripped the entire length of the route in June this year it's time for both updates to the core maps and a more user friendly format for use in the field, especially when offline. This is something I flagged a few months ago and have dabbled with a little, but I have now decided to start working on it over the coming year. Part of the mothballed section from Napier to Wairoa is currently being reopened by Kiwirail.

The original schedule from earlier this year was to publish the current diagrams in the new format. However I now plan to update the diagrams with current aerial photography over the next month or two. The slower part is yard diagrams off historic aerial photography that will maybe be one post a week at most over the coming year because of other priorities. Map work will start with Napier, which is approximately halfway along the route, and go in both directions. I have already published some aerial photos and map work for Gisborne City recently. From Gisborne I will eventually take in the branches but they are a lower priority for map completion at this stage. 

An aerial photo of Napier in 1973.

Otago Central Railway [64B]: Middlemarch-Ranfurly 2 - Waipiata 1

It's two months since I started a series for the Middlemarch to Ranfurly section of the OCR. There weren't at that stage any maps in production for the series. Since that time I have gone back and redone some of the earliest maps with new higher resolution coverage which has thrown the whole schedule back. Right now however I am quickly putting some mosaics together for a number of different stations while I am also updating all the maps as quickly as I can. So I hope to get a fair bit done over the holiday period in terms of progress on a number of the different maps and catch everything up a bit. I had spent quite a lot of time over the past week or so looking at other areas but right now it is just Central I have decided to focus on.

This map is an overview of Waipiata in 1975. Although only just south of Ranfurly, Waipiata was still open at that stage and in fact stayed open almost to the end of the line's closure in 1990, although only as a crossing station. There seems to have been a major stock yards there at the time although not today. Of the railway features you can see in the picture, what remains today is the loading bank and the left hand house. The goods shed was relocated to a site across the main road and a small part of the station building is nearby in Komako Road. A private crib made up of a refurbished wooden carriage and guards van is also in Komako Road.


Saturday, 8 December 2018

Otago Central Railway [61Z]: Alexandra-Cromwell 23 - 2nd Clyde Station 2

Last time I posted the 1972/77 aerial photos of Clyde station had some problems that needed to be fixed. It looks like the aerial images of a 1977 survey were significantly distorted, perhaps the plane that took the photos was not level. Anyone who has used a data projector knows about keystone adjustments you have to make because the lens is not exactly square on to the screen and the shape of the picture is distorted. The same thing will happen when an aerial survey is made and the plane is not level either laterally or longitudinally or maybe the camera is not mounted properly in the plane. Aerial photography generally uses a special plane with a camera mounted in the bottom of it looking straight down. There are other distortions that are caused by varying terrain height and on the modern aerial photography we get from Linz they run it through a computer program called orthorectification to mathematically correct these issues caused by different ground level heights, however the Retrolens photos are just straight scans of the original negative and not orthorectified in any way so especially on hilly terrain you will see such variations. But on what is a fairly flat part of Clyde over 1 mile there wouldn't be expected to be the amount of variation seen and which wasn't seen on the other generations of aerial photos. The result was something like 30 metres displacement in one particular area which is a lot. It took all day yesterday to find a workable solution with a different image of most of the area to the one that was first used.
Here are the two images for 1972/77. The first one is the original, and the second one is the corrected one.

Now that the 1972 series has been fixed, I found that the rail corridor on the 1962 series does not line up with 1972 series, so that also has to be adjusted.