Ancillary files
Georeferencing Files
Georeferencing world files for all available image formats are available at the OS website. The information contained in the georeferencing files is given in the table below.
| Image format | Georeferencing file | Description | Example |
|---|---|---|---|
TIFF | *.TFW | TIFF world file states the X,Y coordinate of the centre of the north-west pixel. | 0.250000 0.000000 0 -0.25000 297000 125000 570999.875000 |
JPEG | *.JGW | JPEG world file states the X,Y coordinate of the centre of the north-west pixel. | 0.250000 0 0 -0.250000 467000.125000 98999.875000 |
ECW | *.EWW | ECW world file states the X,Y coordinate of the centre of the north-west pixel. | 0.250000 0 0 -0.250000 176000.125000 827999.875000 |
GeoTIFF File
OS Imagery is available as a GeoTiff. In a GeoTiff the georeferencing is embed in the imagery file itself.
GeoTiff Header Files
GeoTIFF is delivered with GeoTIFF header information. The information provided is given in the table below.
| TIFF header |
|---|
Tag 256 (image width) |
Tag 257 (image length) |
Tag 258 (bits per sample) |
Tag 259 (compression) |
Tag 262 (photometric interpretation) |
Tag 269 (document name) |
Tag 273 (strip offsets) |
Tag 274 (orientation) |
Tag 277 (samples per pixel) |
Tag 278 (rows per strip) |
Tag 279 (strip byte counts) |
Tag 284 (planar configuration) |
Tag 305 (software) |
Tag 306 (date time) |
Tag 33550 (model pixel scale tag) |
Tag 33922 (model tie point tag) |
Tag 34735 (GeoKey directory tag) |
Metadata Files
All tiles are provided with metadata information. The detail of these is given in the table below.
| Metadata property (as xml tags) | Value examples | Cardinality | Notes |
|---|---|---|---|
copyright | Ordnance Survey, © Crown copyright | 1 | |
kmReference | SU3608 | 1 | |
version | 5 | 1 | |
dateFlown | 2014-07-21 | 1.2 | Single date shown as: CCYY-MM-DD Date range shown as dateFlown Earliest Date dateFlown Latest Date |
kmRectangle | 436000,108000 437000,109000 | 1 | Coords in metres |
resolution | 0.25 | 1 | Metres |
fileSize | 46.877 | 1 | Megabytes to three decimal places |
control | 'GPS and OSTN02' | 1 | Choice of 'GPS and OSTN02™', 'NG from traditional control' or 'Land-Line®'. |
createdBy | 'Ordnance Survey' | 1 | Name of supplier |
correctionType | 'Orthorectified' | 1 | Fixed value |
Where imagery has been merged from more than one source with different flying dates it is possible that small areas of imagery within a 1 kilometre square will not match the metadata values, particularly in rural areas where variations are not significant.
The files are encoded in XML according to an XML schema definition available in the OS MasterMap Imagery layer product downloads.
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