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PostPosted: 29 Sep 2015 18:30 
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Joined: 05 Jan 2011 16:45
Posts: 1057
There won't be any real new features in TransDEM 2.6, apart from full T:ANE support, of course. Nonetheless, a small number of subtle enhancements will be made to existing features. One of these will be support for the O/S 25 inch to the mile map (around 1:2500) from 100 years ago, currently digitized by the National Library of Scotland and made available on a Map Tile server. The digitized map sheets cover most Southern England counties at the moment, at least partially, in particular: Cornwall, Devon, Dorset, Hampshire, Sussex, Surrey, Kent, Oxfordshire, Buckinghamshire, Essex and London.

Earlier this year I added the settings for the 6 inch to the mile map (1:10000) without any need for code changes.

The 25 inch is a different beast, though. The map tiles are provided under several different addresses (URL), namely one for each county. And the tile sets are incomplete. Two additional map tile sets, called “England Holes” and “Holes 2”, are there to complement the county sets.

The rather stringent organizational structure of map tiles settings in TransDEM so far only allowed 8 different tile types per provider and had to become more flexible to accommodate the 13 addresses in use for the 25 inch map today and more in the future.

And the current implementation of the TransDEM map tile client would not tolerate missing tiles. A tile requested from the server had to be delivered back to the client. If the server replied with an error instead, TransDEM would abort the entire request. To recapitulate: each tile is 256 x 256 pixels (de-facto industry standard), and TransDEM can pack up to 8 x 8 = 64 tiles into one request, to fill a 2048 x 2048 px image.

There will be a new option in the map tile settings for TransDEM 2.6, to continue on missing tiles. The space for the void tile will be left empty, or more precisely, left transparent. This will make the “hole” concept work. If the “county” set does not deliver, a complementing “hole” set might have the data. With translucency for missing tiles, superimposing both sources may produce the whole picture.

On the organizational side, tile set types per provider will now be unlimited and can be freely named. The limitation in the past was for a purpose, though: To allow updates and replacements without causing too much clutter. To keep settings consistent in the future, I am adding a unique key to each setting. This key comes as a GUID, a Globally Unique Identifier, also known as UUID, Universally Unique Identifier, a well established concept for such purposes. The key may look ugly if you see it in the xml file, but all the handling will be done by TransDEM. The only important thing here is to never hand-write such a GUID. A proper GUID is created by a rather sophisticated algorithm. TransDEM gets all the new keys it wants from the operating system. (In 2.6, GUIDs are only added to map tile settings, the WMS settings structure will be changed later.)


Some pictures

25 inch tiles for Oxfordshire in the “Oxford” set, with huge gaps:
Image

Complementing tiles in the “Holes 2“ set – we almost always need at least two sets to go with:
Image

Oxford Station as an example, starting with the “new popular edition” (1945-47) 1 inch OS map (1:63360):
Image

The historic 1:25000 (1937-61) is next:
Image

The 6 inch to the mile at a higher zoom level (1:10560, 1842-1952):
Image

Finally the 25 inch to the mile (1:2534, 1841-1952). For this spot almost all tiles are in the “Holes 2” set:
Image

Comparing 1:25000 at the top, 6 inch (1:10560) in the middle and 25 inch (1:2534) at the bottom:
Image

All the detail of the 25 inch with a bit of 6 inch at bottom right:
Image

In the settings dialog, a textbox to edit the tile type name (unless it's a predefined type name) and a new checkbox to set transparent mode (not recommended for other tile servers).
Image

Finally, the settings in xml format, with the new GUID key.
Code:
<Provider name="Historic UK 25inch" guid="12b959ad-1b4f-4afa-809f-ca4cdf024060" >
    <URL name="Cornwall" guid="dea19f0e-9827-4207-8a44-5370d56921e4" addr="http://geo.nls.uk" prefix="mapdata2/os/25_inch/cornwall/" standalone="1" type="8" postfix=".png" ignoreVoid="1" >
      <Matrix prefixClm="/" prefixRow="/" minZoom="1" maxZoom="18" order="2" />
      <Mercator origLat="90" origLon="-180" signLat="-1" signLon="1" projection="4" />
    </URL>
    <URL name="Devon" guid="087abeb4-fdf7-4a4e-9e40-86f02c88c658" addr="http://geo.nls.uk" prefix="mapdata2/os/25_inch/devon/" standalone="1" type="9" postfix=".png" ignoreVoid="1" >
      <Matrix prefixClm="/" prefixRow="/" minZoom="1" maxZoom="18" order="2" />
      <Mercator origLat="90" origLon="-180" signLat="-1" signLon="1" projection="4" />
    </URL>
...


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PostPosted: 04 Dec 2015 22:54 
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Joined: 05 Jan 2011 16:45
Posts: 1057
geophil wrote:
The digitized map sheets cover most Southern England counties at the moment, at least partially, in particular: Cornwall, Devon, Dorset, Hampshire, Sussex, Surrey, Kent, Oxfordshire, Buckinghamshire, Essex and London.
I noticed today that Wiltshire has been added recently (apart from a few void spots) and they are also working on Scotland.


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PostPosted: 16 Oct 2016 13:22 
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Joined: 05 Jan 2011 16:45
Posts: 1057
The latest edition of the preconfigured TransDEM map tile settings, October 2016, reflects the recent additions to this map, digitizing and georeferencing work carried out by the National Library of Scotland (NLS).

Current coverage for England:
Image

England and Scotland:
Image

Background map is O/S Open Data, also retrieved via Map Tiles (and the NLS again)

This is the current list of counties as seen in TransDEM:
  • Cornwall
  • Devon
  • Somerset
  • Dorset
  • Wiltshire
  • Hampshire
  • Surrey
  • Sussex
  • Kent
  • Berkshire
  • Middlesex
  • London
  • Gloucestershire
  • Oxfordshire
  • Buckinghamshire
  • Hertfordshire
  • Essex
  • Warwickshire
  • Northamptonshire
  • Bedfordshire
  • Huntingdonshire
  • Cambridgeshire
  • Suffolk
  • Leicestershire
  • Rutland
  • Lincolnshire

NLS has also two other tile services, named "England Holes" and "England Holes 2". These may have tiles missing from from he county service, e.g. Oxfordshire.


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