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geophil
 Post subject: Geo Data - Great Britain
PostPosted: 08 Jan 2011 13:08 
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Joined: 05 Jan 2011 16:45
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UK Ordnance Survey Land-Form Panorama®

Land-Form Panorama is a 50 m terrestrial DEM for Britain, offered free of charge from Ordnance Survey as part of its Open Data initiative: http://www.ordnancesurvey.co.uk/oswebsite/opendata/

Quality should be at least quite as good as SRTM 3 arc sec, due to the slightly better resolution and the advantage of terrestrial over orbital DEMs.

The package can be downloaded from the Open Data “Supply” page. Download size is approximately 530 MB. It contains the data for all of Britain in three different file formats. TransDEM supports the raster variant (DTM) in ASCII grid format (aka ESRI grid). File type is .asc.

Data is packed into tiles of 20 x 20 km and structured by O/S grid squares. To find the grid square, an overview map should be loaded in TransDEM and the coordinate system switched to OSGB36. Grid square codes are shown in the TransDEM status bar, if the View | Show grid square option is activated. The numerical digits in the file name indicate the 20 km tile in square coordinates, the first digit for the easting, the second digit for the northing.

The tile files can be opened in TransDEM as ordinary DEMs. TransDEM will detect that the coordinates are not geographic and ask for the coordinate system. If the coordinate system has not already been switched to OSGB36 in the main menu it must be set so for each tile file individually.


Last edited by geophil on 08 Jan 2011 13:28, edited 1 time in total.

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geophil
PostPosted: 08 Jan 2011 13:26 
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Joined: 05 Jan 2011 16:45
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Streetmap.co.uk

This map data source offeres O/S topographic maps. It requires entering of a location to obtain a first map. You will find the topographic maps 1:50000 and 1:25000 by clicking on the scale buttons below or right of the map panel. In default mode the map window has an extension of 3 x 3 km (600 x 600 pixels) for the 1:50000 map. “Large map” creates a map clipping of 5 x 5 km (1000 x 1000 pixels) but requires a screen resolution of at least 1280 x 1024 pixels (and browser full screen mode). Below the map to the left you will find a location field that should be set to O/S grid coordinates. Set this to a full 1000 m. Example: 450000,275000 (Rugby).

For a 3 x 3 km map 1:50000 the south-west corner coordinates are obtained by subtracting 1500 for easting and northing, and the north-east corner by adding 1500. For the 5 x 5 km map the value is 2500.

In 1:25000 this equals +/- 750 m for the 600 px map and +/- 1250m for the 1000 px map.

In TransDEM you can use corner georeferencing if you copy and paste the entire screen and then apply a clipping mask.
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BigVern
PostPosted: 29 Mar 2011 03:26 
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Joined: 28 Mar 2011 03:35
Posts: 83
Bing Maps (formerly MS Live Local) now includes an option to switch the display to an OS map for UK locations. I wonder if there's any way of getting the map tile server to see this layer of data which could them be seamlessly overlaid on the DEM.
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geophil
PostPosted: 29 Mar 2011 16:04 
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Joined: 05 Jan 2011 16:45
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Very interesting. I will investigate.
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geophil
PostPosted: 30 Mar 2011 18:11 
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Joined: 05 Jan 2011 16:45
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OS layer identified. Updated TransDEM Sample Settings are available on my website : http://www.rolandziegler.de.

To access the OS 1:50,000 and 1:25,000 maps on the MS server, choose "MS Virtual Earth" (hosts are still named Virtual Earth, unimpressed by newer marketing names like "Live" or "Bing". Then switch to tile type "Other 1"

You get the 1:50,000 map for zoom levels 10 - 13 (makes sense only with zoom level 13) and the 1:25,000 map with zoom levels 14 and 15. 14 should normally do.

1:25,000 will require the 5m grid in Trainz.
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Jerker
PostPosted: 31 Mar 2011 04:49 
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Joined: 30 Jan 2011 13:03
Posts: 170
G'day geophil,

Thanks for that, Roland. I couldn't find the 'option' that Big Vern spoke of on the Bing web site but your updates certainly work a treat. I must admit, I wasn't all that impressed with the resultant image 'resolution' (read 'clarity'/'sharpness') as reproduced in the TransDEM workspace (despite the reproduction quality of the map in the Tile Map dialogue screen being absolutely superb) when downloading the larger sized maps (1536 pixels, although I didn't initially try the 2048 setting) but at 1024 pixels, I was much happier with the quality in TransDEM . Here's a sample of my 'concern', although this is with the largest setting (2048) which is a much better reproduction (almost equal to the 1024 quality) than that obtained with the 1536 setting..

Image

...nonetheless, this should keep me happy for a while..

Jerker {:)}
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geophil
PostPosted: 31 Mar 2011 09:30 
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Joined: 05 Jan 2011 16:45
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Ah. Birmingham, Digbeth Basin, Grand Union Canal. A challenge for boaters (locks and tight bends) but not the prettiest part of town.

Regarding sharpness and clarity of the image: There are a two issues with map tiles and topographic maps; Scale and projection.

The OS maps are raster maps, so are map tiles. But scale does not necessarily match. This requires resampling and adds blur.

Then we have projection. OS maps are OSGB36, a Transverse Mercator Projection. Map Tiles are standard Mercator projection. The conversion will introduce some distortion and add more blur. The TransDEM Map Tile preview window shows the (standard) Mercator projection.

The TransDEM main window shows the native UTM projection of TransDEM. As the name says, UTM is another Transverse Mercator projection, however, parameters are different to OSGB36. This final conversion will add even more blur, but it will also reduce some of the distortion of the map tile. This may explain why the image in the TransDEM main window appears sharper.

The size of the image, 1024, 1536 or 2048 pixels, only affects the initial display in the TransDEM main window (fit to screen). Scale of the map clipping itself will always be the same and only depend on Map tile zoom level.
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BigVern
PostPosted: 01 Jul 2011 08:19 
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Joined: 28 Mar 2011 03:35
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http://www.sabre-roads.org.uk/maps/

Another good resource for old UK maps. The best ones are under Historic NLS/Old Ordnance Survey.

I can't see any associated WMS with the site however, so resource gathering is going to have to be via clippings and a paint programme!
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geophil
PostPosted: 02 Jul 2011 10:21 
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Joined: 05 Jan 2011 16:45
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Vern, it looks like Map Tiles. Will need some analysis.
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geophil
PostPosted: 04 Jul 2011 10:39 
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Joined: 05 Jan 2011 16:45
Posts: 1489
Some of the maps offered at the http://www.sabre-roads.org.uk/maps/ web portal are compatible with Map Tile de-facto standards.

Copy the following code section into a text editor, save as an xml file and import into TransDEM with the Map Tile Client / Settings.

There are 4 tile types configured:
"Map" for "Seventh Series"
"Other 1" for "1:25000" (incomplete)
"Other 2" for "Historic NLS Old Ordnance Survey"
"Other 3" for "New Popular"

Code:
<?xml version="1.0" encoding="iso-8859-1" ?>

<TileServer version="1.0" >
  <Provider name="8 Historic UK" >
    <!-- "Map" for "Seventh series" -->
    <URL addr="http://sabre-roads.org.uk" prefix="maps/tiles/7th/" postfix=".jpg" standalone="1" type="1" >
      <Matrix prefixClm="/" prefixRow="/" minZoom="6" maxZoom="14" order="2" />
      <Mercator origLat="90" origLon="-180" signLat="-1" signLon="1" projection="4" />
    </URL>
    <!-- "Other 1" for "1:25000" (incomplete) -->
    <URL addr="http://sabre-roads.org.uk" prefix="maps/tiles/os1/" postfix=".jpg" standalone="1" type="4" >
      <Matrix prefixClm="/" prefixRow="/" minZoom="6" maxZoom="15" order="2" />
      <Mercator origLat="90" origLon="-180" signLat="-1" signLon="1" projection="4" />
    </URL>
    <!-- "Other 2" for "Historic NLS OS" -->
    <URL addr="http://t3.uk.tileserver.com" prefix="_os1/r0/" postfix=".jpg" standalone="1" type="5" >
      <Matrix prefixClm="/" prefixRow="/" minZoom="1" maxZoom="14" order="2" />
      <Mercator origLat="90" origLon="-180" signLat="-1" signLon="1" projection="4" />
    </URL>
    <!-- "Other 3" for "New Popular" -->
    <URL addr="http://a.ooc.openstreetmap.org" prefix="npe/" postfix=".png" standalone="1" type="6" >
      <Matrix prefixClm="/" prefixRow="/" minZoom="6" maxZoom="15" order="2" />
      <Mercator origLat="90" origLon="-180" signLat="-1" signLon="1" projection="4" />
    </URL>
  </Provider>
</TileServer>
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