Friday, 7 February 2020

Palmerston North Gisborne Line [0X]: Volume 5 Progress Update 24

Welcome to the Volume 5 Progress Update 24. We are moving on steadily with our plan to publish the full volume online not later than tomorrow, Saturday 8 February, 2019 and things are working to schedule.

The last couple of days have been spent expanding the historical aerial coverage of Napier to what can be reasonably achieved in the time available. This screenshot shows a part of we now have to look at which we are working on updating our maps from.

The view of Napier in the GIS.

We discovered that we can get a full NZR "station" survey set of Napier in 1973, including all the way up into Ahuriri and even the south end of the Westshore bridge, except for the Port area which has a full NZR "station" survey set from 1970. However you'll see there is no coverage of the wharves in the top right corner. The reason for this is it was becoming too difficult to overlay the historical aerial photos onto the current layout of Napier Port because in 50 years it has changed so much. As the main historical features are the tracks on the wharves, which can actually be traced anyway for the most part off current aerial photography because they are still there, we felt it was not worth the extra work to produce the historical mosaics for the port area.

This also means where the 1973 imagery joins to the 1970 imagery, only one actual 1970 image has had to be used so the changes at that junction will hopefully not be too much of an issue. There is one other place where an aerial image from a different era is used and that is the coverage of the Robert Holt siding (the premises are in Angus Place and the siding is distinctive because it includes a bridge). Here we were able to locate an image from the NZR corridor survey from 1983 that covers the whole siding. This siding used part of the original main line route between the Ahuriri junction and the Westshore bridge after the main line was diverted in 1990 to make way for a future motorway. This section of the track is actually still in place. The rest of the siding is also still in place up to the first bridge except for where the motorway has been built through, which must have seen it lifted (it actually did cross the road before it was turned into a motorway).

We do not have time to show any other era of Napier (for example, 1983 from the corridor survey for the main line only is a possibility, as are earlier eras from non-NZR coverage), so it will be represented as just 1973 in the maps although as mentioned, it is mostly 1973 with one small part of the yard at the Port in 1970 and one siding in 1983.

So having this coverage now in the GIS, we will see how much time we have to add a few extra tracks etc to the diagram, but it has to be done pretty quickly as not much time is available before deadline.

We have also confirmed the use of aerial photos for the other areas that they were already drawn up for. These are Terrace End (Palmerston North), Woodville, Dannevirke (including Tapuata),  Marakeke and Waipukurau.  Again we will check what is shown on the diagrams to see if we have enough time to add any extra features that are not there already.

The big plus is that having already generated a full set of maps for the corridor two weeks ago, we just have to add in a few extras here and there to the existing set, so actually completing is a much smaller task than it would be if we had waited until finishing all these changes and then pushing out the full set of maps from scratch. At the moment there are 279 diagrams and 408 aerials. The base set of maps are the diagrams with one diagram for each physical aerial covered that combines all historical eras into one. The aerials file names all use the sequence number for the same area that the diagram with the same sequence number uses (from 001 to 279 in this instance) but with suffixes which are generally the year that the aerial covers, so for example you have D023 covering part of Woodville and then you have A023-1946, A023-1962, A023-1972, A023-1983 and A023-2015 covering five historical eras of aerial photography. 

For most of the maps there would be in this example only A023 which would be the current aerial photography for the area, which in practice is a range of dates we have not tracked due to using a global WMTS layer for the whole of NZ that LINZ makes available. In some areas we don't use this global layer, instead we have manually selected a particular WMTS layer for that particular area. Having the use of the WMTS layers has removed from us the requirement to download all the aerial photography for the entire corridor which speeds things up a lot, but we do still have to download areas that we need to create historical mosaics for, in order to lay everything out in Gimp. So for example Napier, we downloaded 3.9 GB of tiles at 0.1m resolution the other day, which when opened up in the Zip file for extraction contained 373 actual tiles, and we needed 60 to cover the area we were working on. In practice, a few were able to be taken out again later or were not needed, so that we can save a little bit of disk space for the Gimp project file because all the mosaics we have created so far for the maps across all of NZ use a huge amount of disk storage, well over 1 TB.

Once there is some time an article about Napier itself and possibly articles for some other areas may well be published - for the last two weeks we have only produced these progress reports.