[OSM-talk] New Popular Edition maps, and postcode collection

[Nick Black]

Very cool.  Any plans for a WMS?  It would then be trivial to ammend
NickW's JOSM-Landsat plugin to show the maps in JOSM, allowing very
fast digitisation.

Nick

On 10/24/06, Dominic Hargreaves <dom at earth.li> wrote:
> On Tue, Oct 24, 2006 at 03:09:49AM +0200, lars wrote:
>
> > Great work!  But the map doesn't come out quite as detailed as I
> > had hoped and it looks a little unsharp.  In particular the
> > sharpness seems to vary with folds and bends in the map, e.g.
> > http://www.npemap.org.uk/tiles/map.html#323,206,1
> > http://www.npemap.org.uk/tiles/map.html#495,123,1
> >
> > What technology did you use to digitize the map?  Did you document
> > the process?
>
> I expect that Richard can explain how the scans were produced. The tile
> production roughly went as follows:
>
> - Open scan of map sheet in the Gimp.
> - Rotate the map so that the grid lines are horizontal/vertical
>   (generally a 1-3 degree rotation)
> - Apply a trapezoid transform if necessary to get the edges of the map
>   (as close to as possible) parallel.
> - Crop the image to just the map (removing the borders)
> - Scale the image to 5000x5625 pixels (so each grid square becomes
>   125x125 pixels). The original scans, including the borders, were
>   around 5500x6500, +- a few hundred pixels.
> - save as JPEG
> - split into tiles with a bit of perl and Image::Magick
> - rename the tiles into their final location with some more perl
>
> The rotation, trapezoid and scaling will have all contributed to the
> deterioration of the image, but was necessary to accurately geocode the
> map (and indeed to display it on a tile-based display system).
>
> I would estimate that this process took us around 15-20 man-hours for
> the maps that we have.
>
> Of course, as explained in the licence, the maps weren't pristine copies
> to start with; some of them were quite worn, had markings on, or were
> not very flat.
>
> Cheers,
>
> Dominic.
>
> --
> Dominic Hargreaves | http://www.larted.org.uk/~dom/
> PGP key 5178E2A5 from the.earth.li (keyserver,web,email)
>
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