Otago Central Railway [4]: Mileposts

Today I decided I was going to put mileposts in. This is possible because of the detail on the chainage charts. First issue to resolve is how to display them. In the OSStations table I have currently set up mileposts with a choice of either km or mi.ch as units. This means miles can be decimalised as miles and chains, which is like displaying hours and minutes as a decimal, because the base system for a chain is not the decimal system, just like minutes is not decimal. The number of chains in a mile is 80 chains, not 100. So I have decided to create a third possible unit, M, which is going to be decimalised miles. In other words, if chains were the basis of this, I would have to convert them to a decimal mile before entering their value. Whilst we may recognise mi.ch it is confusing for non technical people to understand that a decimal point doesn’t mean what it should in this context.
So in starting to do this I discovered the value of it almost immediately because I found errors in bridge numbers. I used the bridges as a reference point to measure out the milepegs and found pretty quickly that the bridge I had marked as 36 was actually a culvert and bridge 37 needed to be renumbered to 36. Then the real bridge 37 was at a point where I hadn’t even noticed it up to now. The reason of course why it is so hard to identify the actual bridges is that small bridges and culverts (when the latter are built in a similar style, as some are) are often very similar in appearance and therefore it is hard to know which is which. Without the chainage charts you would have to try to spot them on the ground and some may well have their number labels missing in any case. Anyway fixing up where bridge 37 was meant an accurate measurement for the nearby 41 mile peg. The tricky question is whether to put the mile pegs in on the Taieri Gorge Railway as I can only do this back to Pukerangi which means about 12 pegs. But we may be able to estimate a few more from Dangerfield & Emerson’s charts of bridge abutment or tunnel portal metrages. If I use those tables then perhaps I will have to put them in kilometres. Anyway putting those in is not a high priority at this stage, only for beyond Middlemarch to start with.
From that point of having fixed up some stuff and putting in all the milepegs starting from 40 at Middlemarch (which is a chain further westing compared to where I marked it as the end of line, being effectively in the Cardigan St road corridor) through towards Hyde. Why am I putting so much detail into the Otago Central compared to a lot of other rail corridors (live or dead)? Mainly because I want these maps to be useful to a lot of people, and they can potentially reach a much wider audience than the maps of the other routes. The OCRT is our biggest rail trail, and I hope to cycle it myself one day. Having all this detail in appeals to railfans like me who want to know what was happening at a particular place, and this is why I am working so hard on this route. Actually the work is at about the same level as what I have been doing where possible with other routes but it does have more of a significance for the rail trail because of its nature compared to a live rail route. The use of the modern Linz aerial photography is something I am just starting to do a lot of and I am picking up details on the ground because of it, since outside main centres GE resolution isn’t that great. Of course the Alcam maps also show good detail and using them is what has convinced me of the merit of downloading the Linz stuff.
So a lot of today was fixing up bridges and milepegs. The bridges I got from Linz were misrepresented in a lot of cases (way longer than they actually were). Obviously Linz employs some lazy cartographers going by all the issues I have to fix up with their data to make my maps a high quality. I also found this recently with Main North Line aerials of the earthquake damage around Kaikoura. So it is not beyond reasonableness to use their aerials to fix up a lot of maps, but I doubt I can be bothered doing all of them this way, especially the North Island stuff.