[OSM-talk] New Popular Edition in JOSM

[Nick Whitelegg]

> > I would like to announce the addition of New Popular Edition
> > support to the
> > landsat plugin in JOSM.
>
> This is excellent again, thank you.
>
> But now I'm a bit worried. The tracks in my area don't align. (And no, it's
> not changes to the street pattern!) If I move the NPE maps to align on a
> key point, then they quickly diverge in all directions from the point.

I'd be surprised if it's that bad - maybe it's an issue with that particular 
NPE map. Earlier today I got good alignment in an approximately 5km x 5km 
area on one NPE tile, and 2km x 2km on another.

> Most 
> of the nodes are mine, but not exclusively, and mine have always joined up
> with other people's in my area remarkably accurately. The River Cam was
> traced (not by me) from Landsat, and taking into account the Landsat
> translation which I've now mostly corrected, that doesn't match either.

> I *think* it is nearly all scale (at least in a small local area), not
> rotational. It's nearly all (though not completely) a North-South
> difference, amounting to maybe 50m in 1500m, but the north-south divergence
> gets greater the further east of west you look from the point as well as
> north or south, i.e. while the difference is mostly a vertical
> misalignment, it gets worse the further you go in *any* direction.
>
> (The grid squares on the NPE layer are also elongated vertically)
> Should I be worried about all the data I've entered? Can I use the NPE
> layer for anything useful with any confidence?

I guess Nick Burch's reply answers this, and his reply mirrors what I've seen 
- the further you go from the point of alignment, the more 'off' it is. I 
would say that as long as you align the NPE map with existing OSM data within 
2-4km of the feature you want to add using the NPE layer, it'll be fine. To 
that end it works best if you want to fill in information in area where there 
is already OSM data.

I think I did all the projection code correctly (used a third party library). 
If anyone does think it's a projection error the code which does the 
projection is in SVN under 
utils/josm/plugins/landsat/src/landsat/OSGBImage.java.

Nick