Alignment of NPE maps?

Tony_Q · 2007-03-30T22:01:49.000Z

Using JOSM, I have the NME maps available through one of the plug-ins. How well aligned are these old maps?

The reason I ask is that all the existing nodes, segments and ways in the area that I’m working on seem to be shifted a little, and my own GPS tracks don’t obviously line up exactly with either the nodes entered by someone else, nor with the NME maps.

Have others had this problem as well? If so, which data do you believe?

Thanks,
Tony Q

Lambertus · 2007-03-31T11:40:59.000Z

Can you give an estimate of the deviation of the NME maps and the GPS tracks? I have some routes near my house that I track regularly as part of other routes and while most tracks all seem to be withing a roads width, some of them are at least 10m, perhaps even 20m off, due to poor receiption caused by e.g. bad weather or clothing cover… However, there are some known problems, while a different projection is used, the deviation is only a few meters. This could be solved by calibrating the maps. Not sure if this is a problem with the NME maps though…

Ben · 2007-03-31T18:28:11.000Z

I only use NPE maps to give an inpression of what things lie were comparitively. There is no reason why they should be 100% correct either, infact I would asume there far from it, and gps data should be the what people stick closely to, as threw averageing it can be made very acurate. Otherwise if 1 person offsets all ther gps data so as to line it up to NPE maps, and another person does not, then the 2 areas are not going to be comparitievly accurate, and not line up.

Traceing and referencing are completly different, and I don’t think NPE offers the sort of level of detial that really justifies tracing the data into osm, due to lack of street signs, amenity’s and over all acuracy, I do not trace from NPE at all. NPE can give a ruff idea, and help a person understand what the set of dots in front of them might mean, but it shouldn’t really be used with any confidence in itself. After all, gpx data is raw data gathered by OSM users, while NPE maps are data that has been transfered an unknown amount of times, and then transfered onto paper, with making the map clear being more inportant than making it bang on acurate. The data is also at least 50+ years old, while gpx data may only be miniuts old!

Tony_Q · 2007-04-06T21:51:05.000Z

Thanks for the responses. I’m seeing misalignment of perhaps 20-40 metres. However, I have just discovered that there is a button to shift the map layer, so I can correct this myself. With regard to the age of the data, I realise that some map data such as roads may change over time, but railway lines don’t! They could, however, be out on the original maps and no-one would know … until now.

bruce89 · 2007-04-10T20:32:28.000Z

There appears to be something wrong with the WMS plugin, I can’t link to the ML message as the server is down ATM.

Lambertus · 2007-04-11T08:22:46.000Z

bruce89:

There appears to be something wrong with the WMS plugin, I can’t link to the ML message as the server is down ATM.

AFAIK the DB and wiki server have been down for most of the day.

TAK-1963 · 2008-04-20T14:22:42.000Z

Hi, I am new to this project and I have started in Vietnam the Nha Trang area. My traced tracks apearing about 50 meters left from the main road along the coast line.

emj · 2008-04-20T20:24:44.000Z

Hi TAK… Please start a new thread if you want to ask a question…

So as is stated in this thread, it might be the case that your tracks are correct and the other is wrong. You never know it’s specific from case to case.

Getting a good GPS tracks can be hard, and if you don’t have a GPS that stores the accuracy in the logs it might be even harder to judge when you have a good GPS track.