[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