[OSM-talk] quality of drawn way

[Simon Hewison]

Mike Collinson wrote:
> Arriving recently in the UK and applying the same principle to NPE, I find it is only possible to align very, very locally. I'm not familiar with the stretch properties of  map paper over time but the size and local randomness of the misalignment makes me suspect that it is due to inaccuracy in the original survey and not paper or scanning artifacts.  I'll be paying more attention to the apparent location of the grid lines to confirm that.
> 
> If anyone is interested in looking at this further, go to Wharfedale, Yorkshire, UK http://www.openstreetmap.org/index.html?lat=54.12364148710909&lon=-2.048039022841875&zoom=11 in JOSM.  The roads are GPS surveyed and marked source=survey. The Landsat data needs shifting a few pixels due south. The NPE match is good overall but wanders at the local scale.

I've found that NPE takes a lot of calibration via the JOSM plugin as you go 
further west and north. Around London, it's quite good, but if you go to about 
4 degrees west (eg. Pembrokeshire), the projection difference between the OSGB 
grid and Mercator means that you have to tweak the alignments every km square, 
and even then you have to take into account the difference within the grid square.

-- 
Simon Hewison