Friday, 17 May 2019

Project Diary 2019-05-17

We try to post at least once a week depending on what we are doing in this project. Most of the posts are about specific volumes or regions we are working on. Other times there will be a progress report for the whole project like there was last week. This week it will just be a diary entry because whilst we have been doing a lot of map work this week, not a lot of it has related specifically to NZRM.

This week the majority of our time has been taken up with getting a complete set of maps for Christchurch City. This meant downloading a lot of stuff from Land Information New Zealand, because they have a 3.5 GB limit for the estimated size of each download. As it happens, it is more like 5 GB actual download in a lot of cases. But it meant that at a pixel spacing of 0.075 metres, there are a LOT of layers for the whole city. It works out to something like 60 GB. If you have a few dollars you can get them to courier the data layers to you. With the fact we don't have any spare cash to spend, we just settled for splitting up the city layers into a series of downloads to get all of it. There are some overlaps which means we don't quite have the expected efficiency and because we inadvertently got some gaps between downloads we had to make some extra downloads to be able to fill in those gaps.

So we now have Christchurch City covered for 2018 (central only), 2015 (whole city), 2011 just after the quake (central only) and c.2010 (actually between 2004-2010 and for some reason the dates aren't more precise) which again is the whole city. We also have some historical retrolens layers to overlay at some point. We did consider downloading all the 2011 imagery and in fact did set up a series of downloads in Linz but haven't actually executed those downloads because that imagery is at 0.1 metre pixel spacing and while it is very good it is also just after the quakes so it does have limits. But it is a shame that there isn't high resolution imagery before then that can be downloaded. Even 0.3 metres would be better than the 0.75 metres 2004-2010 stuff.

As far as the NZRM project actually goes the work this week has been on the Otago Central line. First up is to redo the Cromwell Gorge section with the Retrolens scans of survey 1452 which are distinctly sharper than the original ones we paid for a few years ago, and then particular stations. At the moment Omakau-Cromwell is being considered as one Gimp project covering a number of stations. It is separate from the Cromwell Gorge mosaics because of differing resolutions. The Cromwell Gorge part was originally done at 0.75 metre base imagery because that was all that was available for the whole section, but in 2017 the full area became available at 0.4 metres. But initially all that we did was scale the 0.4 metres to 0.75 metres and overlay it with the 0.75 metre stuff. Now we have scaled the 0.75 metre base to 0.4 metres so as to be able to use this scale base imagery for the Gorge section.

Monday, 13 May 2019

Project Development Report [2019I]

This week we have continued working on downloading Linz base imagery and Retrolens historical imagery for the entire MSL corridor. We currently have the base imagery down to about Tumai (just south of Moeraki) and Retrolens down to Pareora, and progress has been a little slow this week, because we took some time on the following subprojects:
  • testing the replacement for grid segmenting for most parts of the maps project, which is to scale 0.3 or 0.4 metre imagery to 0.15/0.2 metre size and use doubled dimension tiles in Qgis.
  • writing a script to create and copy the sidecar files for the doubled dimension jpeg tiles automatically to save on a lot of manual steps especially with multiple generations of historical images that all need these files duplicated and having to change the pixel size in the world files to match the larger mosaic layer sizes.
  • converting the Dunedin-Burnside part of the Dunedin-Mosgiel mosaic tiles Gimp project from a sectioned canvas format to a linear canvas format. 
The Dunedin-Burnside Gimp project is something we have had to work on this week because of wishing to extract the layers for Hillside Workshops, an earlier version of which are displayed at the bottom of this post. Being able to convert to a linear canvas means being able to remove a lot of overlapping layers between the canvas sections. As all of the base layers are always displayed, it speeds up selecting layers for display as well. Since extracting these views of Hillside, we have fixed a few issues with the overlapping of different layers so that one place in particular where quite a rough cut is visible between two layer going across the middle of the workshops site, this has now been made much smoother.

As well as the southern part of Dunedin going out as far as we can with the 0.125 metre resolution urban imagery until we have to switch to the 0.3 metre or 0.4 metre stuff that covers probably the rest of the way to Invercargill except for probably a small number of townships that will have something of higher resolution, we also have to go north to the limits of the Dunedin coverage in that direction so we are working to get that sorted today.

Last week we also downloaded 0.075 metre coverage of Timaru City and will have a look to see what is available going further south. Retrolens coverage downloaded is currently down to Pareora, and rural base imagery down to Tumai. Finishing all the downloads for the MSL corridor and retrieving the 100 GB or so of disk space used remains a high priority so that is one reason why the work seems slow at the moment.

 Hillside Workshops as seen in 1972. As mentioned above a rough overlap can be seen between two layers vertically in the left hand third of the image, this has been correct in current aerial mosaics.
The same Hillside site seen in 2013, which is the latest aerial imagery of Dunedin at high resolution. Now a bit out of date with further changes at Hillside Shops since it closed a few years ago.

Monday, 6 May 2019

MSL Timaru-Glenavy[1]: Normanby-Pareora Realignment

Between the locations of 179.5 km and 181.5 km on the Main South Line between the stations of Normanby and Pareora there has been a realignment of the rail corridor. The corridor used to be about 50 metres closer to the beach than it is now. We are indebted to the late Colin Kemp, a train driver for Kiwirail, for bringing this to our attention.

From aerial photo data we estimate the realignment was carried out around the year 1980. No records with titles specifically referencing it have been found in Archives New Zealand's Archway portal to date.

 Overview of the area with the historical (1942) aerial imagery background.
 The same view with modern day aerial imagery.
Closeup at bridge 97.
Historical aerial imagery at Bridge 97. This appears to show a location of a previous bridge at the site of the current bridge, that was not actually in use in 1942.

A big question to be asked is why it was necessary along this mile-long section to go so close to the seashore in the first place. As far as we can discover, everywhere else along that particular coastline, the railway is at least 50 metres inland and we have not seen anything to suggest other sections of the railway in this area were historically located as close to the seashore as this part of the MSL was.

MSL Timaru-Glenavy [0A]: Intro 1

For our series of articles on the Main South Line we will break the corridor up into sections and these sections are chosen mostly on prominent stations but also in this case a geographic boundary. Glenavy is on the north bank of the Waitaki river which is the historical boundary between the provinces of Otago and Canterbury. The actual boundary nowadays for the Canterbury region is just south of the Waitaki and takes in all of the Upper Waitaki lakes as it is based on river catchment and the Waitaki is considered a Canterbury river.

From Timaru to Glenavy, 60 km, the only settlement of any substantial size is Timaru itself. There is one branch junction at Studholme for the line to Waimate that closed in 1966.  This had an extension into the Waimate Gorge that closed in 1953.

For all of the maps of the Main South Line there are two types of mosaic being produced:
  • Where 0.2 metre  - 0.075 metre pixel size base (Linz) imagery is available then producing tiles without any resizing of the base layer.
  • Where 0.3 metre or 0.4 metre pixel size base imagery is available then resizing this to double the original resolution (i.e. 0.15 - 0.2 metre). To avoid the need for segmented grids splitting each resized base layer into four tiles at the original physical size I am hoping turning off render caching in Qgis will prevent it from running out of resources so quickly as has been a problem in the past with larger size tiles.
In all cases we have for the historical imagery a choice of 1:4300 or 1:4325 NZR station surveys, 1:5500 NZR corridor surveys and 1:8000 highway surveys that are worth doing mosaics from as there is very good visibility of detail on the ground in most cases. We can use some older surveys at 1:10000 or smaller scales up to 1:25000 in a few cases but they are less desirable.

We are currently getting all of the background imagery we need of the MSL heading southwards and will get to Dunedin in a few days and then carry on towards Bluff gathering all the Retrolens coverage along the way and making mosaics and tiles all along the route. We expect to resume drawing the Dunedin maps when we get everything finished as it is a high priority to recover disk space from deleting all of the downloaded stuff that isn't needed.

Friday, 3 May 2019

Otago Central Railway [47J]: Current delay in OCR maps

The current effort on NZ Rail Maps to map the Otago Central Line started in November of 2017 - about 18 months ago. It was at that time with the first of the posts in series 47 that we started the widespread use of the LINZ background imagery and bringing in historical imagery with the mosaic projects. We had at that time hoped to complete the set of maps for the entire line by a series of deadlines which eventually stretched out to the end of 2018.

Since the beginning of this year we decided to temporarily set the Otago Central line aside and work on other projects. One of the reasons for this is that LGGA are still scanning the aerial images for that area and adding new stuff all the time. Rather than doing an area then finding there is new stuff and going back to add it is a good enough reason for deferring the completion of work on maps for railways in Otago.

We just recently discovered LGGA have found survey 1452 which is State Highway 8 that we have used for the Cromwell Gorge has been added so we are currently poring over that to see if their scans are better quality than what we already have. Another example is patiently waiting until finally the one and only good quality scan of Ida Valley became available which was late last year.

We don't quite know when Otago Central will be completed but it is still very much under consideration and being worked on behind the scenes from time to time.

Tuesday, 30 April 2019

MSL Rolleston-Timaru [0B]: Intro 2

So as of today we are back to doing the Main South Line and we are doing it for the same reason as the MNL corridor we just did the aerial imagery of. To free up some disk space with a lot of downloads, and also to have the complete corridor and set of aerial imagery for as many stations as we can find them for. Now we have three useful series of aerial images going south. The NZR corridor surveys, in this case, are from 1984 which is a bit late for many stations that closed before then. We referred to some of these surveys in previous posts about the MSL around Dunedin. So in addition to those we have SH1 surveys for the parts of the MSL corridor that were close enough to SH1. That should be nearly all the way to Timaru with some possible gaps. From Timaru to Pareora is likely to be fairly patchy, and then from Studholme to Glenavy could be tricky as well. South of Oamaru is fairly patchy as well, with the best section being from Hillgrove to Palmerston. So highway surveys have limited utility and we will have to lean heavily on the NZR corridor surveys, but them being from the 1980s rather than the 1970s or earlier is limiting.

So we are just downloading stuff at the moment and extracting the base imagery for the corridor going south from Christchurch. Mosaic projects are not happening immediately because just getting the aerial photography is a big effort and that's where the work is going into, to complete all this as quickly as possible.

RNZAF Weedons Air Force Base was established for stores during World War II and had a railway siding off the Main South Line a little north of the Weedons railway station. Seen here in 1950.

Weedons AFB site seen in 2018, the last remaining hangar at the site has been recently demolished.

 Rolleston in 1972. Apart from the train with apparently a pair of DG locomotives coming off the Midland Line (the lead locomotive is so dark in colour it's difficult to be sure exactly what type it is), the sidings going into the trees opposite the station are interesting because of the wagon turntable in the middle of one of them.

Another shot of Rolleston in 1972 and this one shows the start of the Midland Line and what appears to be the site of a former building (on the RHS) and water vat (on the LHS). The water race across the middle of the photo could have supplied water to the vat. So we assume this could have been a locomotive depot, but if it was, then it must have been about 100 years ago, since the 1942 aerial photo shows perhaps a concrete foundation similar to the above - no actual building.

Monday, 29 April 2019

Main North Line [0E]: Volume 10 Progress Report [4]

As we have reported in the last few posts in this series, we have been busy collecting aerial images for the Main North Line corridor from Christchurch to Picton and this work is now practically complete. Although a few extra downloads from Linz have been needed, most of the work has been completed and 150 GB of disk space was recovered by removing all of the download files that had been previously collected for the MNL corridor, which was the main object of this exercise. The majority of the work has been the effort needed to locate as many Retrolens aerial images of old stations as possible. 

Apart from the corridor surveys from NZR from the 1970s and a small number of dedicated station surveys, we have been fortunate to be able to draw on corridor surveys of State Highway 1, where it has been located close enough to the rail corridor, and since the earlier series of these date from 1961, it has been possible to capture many stations at an earlier time when they may have been open, and have closed by the time the NZR surveys were carried out.

Our knowledge of the Main North Line in Marlborough has been added to by discovering a previously undocumented series of realignments that were made on the former Picton Section prior to 1947/48 which in many cases is when the earliest historical aerial photos are available for the area. One of these is at Hog Swamp Creek just south of Seddon and is seen below.

We assume the key reason was to eliminate and bypass the bridge there, probably when it became due for replacement, as the curve was only slightly reduced in radius.

The next three photos show a series of realignments between Tuamarina and Para.

We don't have these mapped at present and it will be some time before we expect to draw these onto maps as probably mosaics will have to be made to enable them to be traced readily.

As one would expected some other useful discoveries have also been made along the way. 

Just north of Wharanui is the Waima River (previously known as the Ure River). Wharanui was the southernmost extent of the Picton Section, to which the line was opened in 1915. The section between Wharanui and Ward took four years to complete, which included 15 km of track, the No.3 tunnel (currently No.21 on the MNL and known colloquially as the Tar Barrel), and the bridge. This was the last single deck combined bridge on the Main North Line. To our best knowledge there were in fact only two single deck combined bridges on the whole of the MNL, the other one being at Parnassus and that was replaced about 1940. The road bridge at Clarence was originally intended to be a combined bridge, but in fact when the railway eventually reached Clarence in the early 1940s it got its own bridge. The double deck combined bridge at Seddon became rail only in the early 2000s when the new state highway bridge was built, but the redundant lower deck is expected to be reinstated for a cycleway.

Waima River combined bridge in 1969.

By 1972, work was starting to replace the bridge. It looks like the new railway bridge was built first.

By 1975 both new bridges had been built alongside the original. The highway originally crossed the railway on a one lane overbridge north of the river. This was replaced by a new overbridge south of the river, which took several more years to be built.

Another major river crossed in Marlborough is the Wairau between Spring Creek and Tuamarina. We understand there may have been some erroneous suggestions this was a combined bridge but that is not the case.

1937 aerial photo of the bridge. The highway at that time was some distance downstream and did not cross the river alongside the railway, as it does today.

This 1977 aerial shows work was underway to build a new curved railway bridge alongside the existing straight structure. Anecdotally we have heard the replacement was needed due to scouring of piers in the original but have not confirmed this. 

To conclude this post here is a 1986 view of the Awatere River double deck bridge just north of Seddon. There were a number of occasions that the road deck was closed for repairs (the bridge was built c.1902 and the deck was wooden) and generally, a temporary road was put through the riverbed as there was no convenient detour. The route of the most recent temporary highway on the upstream side of the bridge can be seen fairly clearly here (it was different from other occasions) and sealed highway in the riverbed, albeit on the downstream side, was still visible until the new highway bridge was built, after which it seems to have been dug up.

Saturday, 27 April 2019

Main North Line [0D]: Volume 10 Progress Report [3]

We have decided to push ahead with the MNL corridor LDS images and setting up Gimp mosaic projects as a top priority because of the disk space issue. As mentioned before the downloads for this particular corridor are presently using up lots of disk that we want to recover.

As it turns out we already have most of the base imagery downloaded and selected so most of what has been worked on today has been ascertaining how much Retrolens coverage there is of the Main North Line stations. 

NZR had basically two types of aerial surveys done for them: station specific surveys, which are easy to spot because the run number is always A, meaning the survey/run/photo number sequence will usually be XXXX-A-1 through to usually no more than 5, another giveway is the earlier ones always have a scale of 1:4300. The other type of survey done is for a whole route. Generally these were just the main lines and were done in the 1970s. A long corridor like the MNL or MSL will be broken into several surveys that must have been a lot of fun to fly as these long main lines are far from straight so the plane would have made many passes to capture all the different runs that make up each survey.

North of Christchurch there are relatively few station surveys as they are generally only for the major stations such as Belfast, Rangiora, Amberley and Waipara. However for many of the other stations, the route surveys done in 1976/77 often are showing the many small stations that were still open at that time (surprising great number as many are long gone these days). We intend to incorporate these into mosaics later on but for the present we are only setting up mosaic projects rather than actually making mosaics. Deviations and realignments also provide reasons for mosaic making.

The only completed set of mosaics north of Rangiora to date are the ones for Amberley, Waipara, Hundalee, and former Tunnel 4 near Oaro.  As was mentioned before, we did Picton under a different system some time back. These will be redone under the current system. A couple of stations on the Waiau Branch have also been mosaiced and the rest that we have coverage for can also be done in the future.

Between Parnassus and Wharanui the base coverage we have at the moment is the Kaikoura earthquake coverage shot just after the 2016 Rotherham quake. We are currently considering whether it is suitable to use as a background for the maps. At the moment that is what we are using, but if we decide it isn't suitable, there will be a lot of work to download the previous base images and they are not as sharp as the EQ stuff, which is at 0.2 metre pixel size.

Friday, 26 April 2019

Main North Line [0C]: Volume 10 Progress Report [2]

Of late we have been working on some of the rail corridors around Christchurch by amalgamating Gimp projects covering single station sites into projects that cover a whole section of corridor. This includes both the MSL and the MNL. The first one for the MNL covers from Addington to Ashley, which except for the area covering Flaxton station, which appears to be a tiny flag stop between Eyreton and Southbrook, is continuously in 0.075 metre imagery from several different layer groups.

Since we have already downloaded imagery for nearly the whole MNL, we are pushing ahead to get the entire MNL corridor organised in my computer. It is important to do this because we have so many downloaded aerial layers that are consuming massive amounts of disk space on the computers and need this space to store the mosaics that are going to be created for the project. As an example we have currently just over 200 GB of downloads for the MNL and could expect that further mosaics for this corridor might use 100 GB, giving a net gain of perhaps 100 GB. 

We need to do this work for every of the 12 volumes of the maps project but few of them have as much aerial imagery downloaded as for the MNL which has probably got a lot of duplications, but also it is a long corridor and therefore will have a lot of basemaps.

After Ashley, the little station on the north bank of the Ashley River 33 km north of Christchurch, the next section of mosaics would be at 0.3 metres and take us from Sefton through to Balcairn. We skip Amberley and Waipara, which are in 0.125 metre coverage from Hurunui District Council and will be in their own project, and carry on with stations north of Waipara and I haven't really looked at what there is good coverage of. We are not actually drawing maps but we are laying groundwork to be able to draw the base maps at a future time and the mosaics after that. Since there weren't that many major stations on the MNL we are not yet sure what aerial coverage will exist. Addington-Ashley covers really the old suburban passenger network north of Christchurch. Amberley and Waipara have been worked on recently as a separate effort, and north of there we started looking at a few places.

Some may recall there was an earlier aerial mapping effort that produced images of Picton, amongst other areas. That is indeed the case. It was carried out using similar principles but the technique was to overlay the historical aerial images into Google Earth and then trace over them, and then import the traces into Qgis overlaying them on current Linz basemaps for the produced output. This effort has been overturned because of licensing concerns with Google's maps system which we definitely want to avoid. We published a series of articles on Picton in October 2017. We did our first map project in Gimp, which was for Alexandra on the Otago Central Line, in March 2018. Since then we have fully embraced this combination of Linz basemaps with Retrolens overlays produced in Gimp and imported directly to Qgis for the tracing and it can produce historical map outputs as well. This means Picton will be redone in Gimp for a new set of maps sometime.

This need of completing the base maps of a corridor being urgent has caused work to be suspended on the MSL maps for the time being but we expect to be drawing some of them again this weekend even as we continue to finish off the MNL corridor, the only reason we haven't been doing any this week is because of other work priorities.

Tuesday, 23 April 2019

MSL Rolleston-Timaru [0A]: Intro 1

With this particular article I am making it clear I am working towards Volume 11 as a major effort to get something that is actually going to be completed as a volume as soon as possible. This will not be a continuous effort throughout the year but it will be a major focus for the maps this year. At the same time I am refocusing my ambitious schedule that was planned for the year and suggesting it might have to be put out over two or three years.

Rolleston all the way through to Timaru is covered by a 0.3 metre aerial layer. At the moment I am downloading all of what is available in that layer for MSL right down to Waikouaiti and then from there all the way down to Dunedin and then Invercargill will soon follow. Mosaic projects have been assembled over the past few days to cover Lyttelton through to Templeton (the limit of 0.075 metre coverage of Christchurch), and from there will cover Rolleston and any other townships that are in 0.125 metre coverage for the Selwyn District, and from there at 0.3 metres heading south.

We will be using all available NZR surveys for the stations heading south and to match this resolution the 0.3 metre images will have to be rescaled to 0.1 metre size and segmented mosaic canvas used. Last time I wrote about using linear and segmented mosaic projects and indicated a clear preference for linear. However this is only possible where the base imagery is no more than 0.125 m pixel size as too much detail is lost scaling down the NZR images to match larger pixel sizes. At that point I have to bring in a tile grid to sit in the background of the canvas to provide grid indexes for segments and we don't want to duplicate multiple copies of this grid across a linear canvas because there are too many additional layers. Segmenting is actually OK for this situation because the stations are quite a distance apart, meaning no overlap problems, and therefore there is no benefit to a linear canvas.

So I am just about to create the first segmented canvas mosaic project in Gimp for Weedons / Weedons AFB / Burnham and maybe a few other stations heading south as well.

As one can imagine, completing a volume for a line as long as the MSL is quite an ambitious undertaking and it will be staged out and I will take breaks to do work on other areas as I always do. Volumes 5 and 12 in particular are other areas I want to make significant progress on this year and as previously noted there is the schedule I talked about earlier this year and I will look at the standard of completion for other volumes. But to get any of these volumes together I have to download all the aerial imagery for the base maps and that is always a big effort and that at the minimum is what is needed to bring the maps together regardless of what level is produced.

MSL also incorporates previous work done with Methven and Springburn lines and this will be brought in as well. There are no NZR surveys for either line so no issue with having to match NZR survey resolution.

Sunday, 21 April 2019

MSL Lyttelton-Rolleston [0B]: Christchurch-Hornby Intro

Following on from recent efforts to speed up mosaic production, due to having discovered the best way to combine multiple stations or a continuous length of corridor into one Gimp project, I have started doing this with the MSL around Christchurch. Yesterday and part of today has been spent combining several smaller projects into a big one covering Christchurch to Templeton Hornby, which is much of the western suburban corridor for Christchurch itself. There will also be one done for Lyttelton to Christchurch and for Addington to Kainga and Kaiapoi to Rangiora, this one might be taken a bit further north as the stations are further apart so we may be able to get more distance into it. If that was the case it would only go to just south of Amberley at the most. 

The focus is really going on ways to speed up the production of the mosaic tiles and this system of combining several areas in a larger project (up to 100 layers) does speed things up and is only really possible since Gimp 2.10 when they implemented support for projects more than 4 GB. At the moment 100 layers is the practical limit of the computer resources I have, but is also a practical file size limit because of the time it takes Gimp to save a file of that size, which can be as much as 30 minutes (for a 30 GB file). Part of the streamlining is also to do away with all the masking off except in very occasional situations, cropping off the boundaries is easier but I also dispensed with composite aerial tiles that blended old and new together as for historical comparisons just old layer vs new layer gives more surrounding detail for interest.

The last time I worked on this corridor was in May of last year and I was then looking at Christchurch Station in particular but had drawn a project that went from there out to Opawa. That was at the very early stages of my learning how to use Gimp and getting stuff done so it was time consuming with a lot of trialling different things. One of the lessons being learned at that time that was not finally solved until later last year was needing to have background imagery that matched the historical stuff in resolution, and as it can be seen earlier this year, that has been for the surveys that NZR had done for their own use, which often have a scale of around 1:4300 on each image and are very detailed indeed, source imagery of pixel size 0.1 metres or less (0.075 is the smallest pixel size currently being produced by LDS and is generally available for the main urban areas) is needed, and if that isn't what is available then it has to be scaled to match. Hence I spent a bit of time earlier in the year coming up with a way to segment scaled up imagery from 0.3 or 0.4 metres to 0.1 metres so that the NZR surveys could be used to their best advantage. In particular, some of the work recently done in Northland has used that process.

But with the recent work being around urban areas and being able to use 0.1 metre or finer pixel size LDS base imagery, I haven't had to muck around with scaling up and segmenting the source imagery and have just been able to use the base stuff as is. So then I did Dunedin-Mosgiel which was a learning curve of doing the largest possible project size, which turns out to be 100 layers, and from there I went on to do Horotiu-Frankton-Claudelands on the NIMT, which was a learning curve of laying out everything in a really large canvas (in this case one with 1000 million pixels) which is a major step up in ease of use from the way I laid out the stations in Dunedin. Christchurch-Templeton is an interesting one (as will be Christchurch-Kainga) where the corridor is closely aligned to a geographic meridian, meaning a long narrow canvas - the Christchurch-Hornby one is currently 192000 by 21600 without all the tiles yet in place, because that doesn't happen very often in NZ rail geography. Originally I was planning to take it out to Templeton but this was going to push the layer count way over 100 so it has had to be cut back to Hornby, about 9-10 km.

Meanwhile I still did get a reasonable amount of drawing of Dunedin done yesterday and this work continues so I am not slowing down that part too much, because it is important to get that through as soon as possible.

It is imperative to get as much of the base imagery for each project in place as quickly as possible as well, because all of the downloads on one of my computers are taking up a lot of disk space and that space is needed to save the mosaics which are using hundreds of GB so getting these corridors finished for base imagery and then also pushing ahead with the historical maps as well on the corridors is much more of an imperative now.

I think after Dunedin-Mosgiel then possibly Dunedin-Port Chalmers really quickly and then Volume 5 for PNGL is going to be the order of things, but I also do hope to get back to the OCR reasonably soon.

Friday, 19 April 2019

North Island Main Trunk [0C]: Intro 3: Hamilton Urban Area 2

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.
 Hotoriu station.

 Te Rapa Air Force Base.

 Main Te Rapa yard with hump to the far right.
 Te Rapa loco depot 1972.

 Frankton yard.
 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.

 Claudelands 1953.
Claudelands 1975.