[OSM-talk] IoW: New Popular Edition orthorectified

[Laurence Penney]

Andy Robinson wrote:
> I hope one of those anchor points was not the OS HQ in Southampton. They
> might have moved it a bit just to throw you ;-)

Heh, no, just the four corners of the main mapped area.

> Great work...can the same rectification process be used for my older 6-inch
> OS maps do you think?

Yes, the same process would work well providing the map has been turned 
into a single image. Don't bother trying for perfectly aligned scans. 
Some rotation algorithms (e.g. that in imagemagick convert) have trouble 
when rotating by very small angles. I've been using Photoshop for the 
rotations.

I was hoping to have the whole country done before now, but it won't be 
long. Here's the current set that's been done:

http://www.lorp.org/maps/showset.php

Yesterday I wrote a member login system for the site that I'll use to 
track who's assigned to what. I think with collaboration we'll be able 
to get large sets of scanned maps up & running pretty efficiently - at 
least with the "four corners" method.

For orthorectifying scans that are more distorted than simple rotation 
(typically by creases but also by poor surveying), I may add the option 
  to specify as many corresponding points as you like. The actual tiling 
operation then becomes something akin to morphing, to the extent that 
even a London Underground map could be "rectified".

Please don't distribute any of these URLs beyond this list - the tiles 
are currently just at one size (the browser scales them), the 25% and 
50% zooms are therefore inefficient, and I don't want my site to die 
just yet!

-- Laurence