[Talk-GB] reprojected NPE

Tim Sheerman-Chase orders2008 at sheerman-chase.org.uk
Tue Apr 15 16:59:50 BST 2008

> Great work with the NPE stuff,but could I just ask how this differs
> from the existing NPE WMS layer within JOSM?
The existing NPE WMS creates tiles only approximately align with 
features in JOSM because they are in GBOS projection not in JOSM's 
projection. You can see this by the grid lines are horizontal and 
vertical. In the correct projection, the grid lines should be at an 
angle because GBOS north and JOSM (EPSG:4326) north are not the same thing.

The WMS plugin overlays small crosses so the user than manually align 
NPE with OSM features. My way avoids this step (usually). Also, with the 
existing NPE layer, the user can minimize the distortion by requesting 
only small map areas.

As I understand it, Richard is retiling the NPE data from the original 
scans which should noticeably improve the accuracy of the NPE layer (in 
Potlatch or JOSM via my WMS server). This process takes time I'd imagine 
- there are hundreds of thousands of GBOS squares!


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