Web Mapping Illustrated: Using Open Source GIS Toolkits

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National Transfer Format Files (NTF)

NTF files are mostly used by the U.K. Ordnance Survey (OS). For more on the Ordnance Survey, see their web site at http://www.ordnancesurvey.co.uk.

NTF files have an NTF extension.

Data access/connection method

  • NTF access requires OGR.

  • The path to the NTF file is required in the CONNECTION string. It may be relative to the SHAPEPATH setting in the map file or the full path.

  • The CONNECTION must also include a layer number (as per the layer number from ogrinfo, but minus one).

ogrinfo examples

Here's an example that uses ogrinfo on an NTF file to retrieve layer numbers:

> ogrinfo llcontours.ntf ERROR 4: NTF Driver doesn't support update. Had to open data source read-only. INFO: Open of 'llcontours.ntf' using driver 'UK .NTF' successful. 1: LANDLINE_POINT (Point) 2: LANDLINE_LINE (Line String) 3: LANDLINE_NAME (Point) 4: FEATURE_CLASSES (None)

For the LANDLINE_LINE layer, the ogrinfo layer number is 2; however, when referring to this layer in a map file connection, the layer number is 1.

Here's an example that uses ogrinfo to examine the structure of an NTF layer:

> ogrinfo llcontours.ntf LANDLINE_LINE ERROR 4: NTF Driver doesn't support update. Had to open data source read-only. INFO: Open of 'llcontours.ntf' using driver 'UK .NTF' successful.   Layer name: LANDLINE_LINE Geometry: Line String Feature Count: 491 Extent: (279000.000000, 187000.000000) - (280000.000000, 188000.000000) Layer SRS WKT: PROJCS["OSGB 1936 / British National Grid",   GEOGCS["OSGB 1936", DATUM["OSGB_1936", SPHEROID["Airy 1830",6377563.396,299.3249646, AUTHORITY["EPSG","7001"]], AUTHORITY["EPSG","6277"]], PRIMEM["Greenwich",0, AUTHORITY["EPSG","8901"]], UNIT["degree",0.0174532925199433], AUTHORITY["EPSG","4277"]], PROJECTION["Transverse_Mercator"], PARAMETER["latitude_of_origin",49], PARAMETER["central_meridian",-2], PARAMETER["scale_factor",0.999601272], PARAMETER["false_easting",400000], PARAMETER["false_northing",-100000], UNIT["metre",1, AUTHORITY["EPSG","9001"]], AUTHORITY["EPSG","27700"]] LINE_ID: Integer (6.0) FEAT_CODE: String (4.0) ...

Map file example

LAYER NAME ntf_uk TYPE LINE CONNECTIONTYPE OGR CONNECTION "./ntf/llcontours.ntf,1" STATUS DEFAULT CLASS NAME "Contours" COLOR 0 150 200 END END

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