Provided by: libgeo-coordinates-osgb-perl_2.15-1_all bug

NAME

       Geo::Coordinates::OSGB::Grid - Format and parse British National Grid references

VERSION

       Examine $Geo::Coordinates::OSGB::Grid::VERSION for details.

SYNOPSIS

         use Geo::Coordinates::OSGB::Grid qw/parse_grid format_grid/;

         my ($e,$n) = parse_grid('TQ 23451 09893');
         my $gr     = format_grid($e, $n); # "TQ 234 098"

DESCRIPTION

       This module provides useful functions for parsing and formatting OSGB grid references.
       Some detailed background is given in "background.pod" and on the OS web site.

SUBROUTINES AND METHODS

   "format_grid(e, n)"
       Formats an (easting, northing) pair into traditional `full national grid reference' with
       two letters and two sets of three numbers, like this `SU 387 147'.

           $gridref = format_grid(438710.908, 114792.248); # SU 387 147

       If you want the individual components call it in a list context.

           ($sq, $e, $n) = format_grid(438710.908, 114792.248); # ('SU', 387, 147)

       Note that rather than being rounded, the easting and northing are truncated to hectometres
       (as the OS system demands), so the grid reference refers to the lower left corner of the
       relevant 100m square.  The system is described below the legend on all OS Landranger maps.

       The format grid routine takes an optional third argument to control the form of grid
       reference returned.  This should be a hash reference with one or more of the keys shown
       below (with the default values).

           format_grid(e, n, {form => 'SS EEE NNN', maps => 0, series => 'ABCHJ'})

       Options for "format_grid"

       form
           Controls the format of the grid reference.  With "$e, $n" set as above:

               Format          produces        Format            produces
               ----------------------------------------------------------------
               'SS'            SU
               'SSEN'          SU31            'SS E N'          SU 3 1
               'SSEENN'        SU3814          'SS EE NN'        SU 38 14
               'SSEEENNN'      SU387147        'SS EEE NNN'      SU 387 147
               'SSEEEENNNN'    SU38711479      'SS EEEE NNNN'    SU 3871 1479
               'SSEEEEENNNNN'  SU3871014792    'SS EEEEE NNNNN'  SU 38710 14792

           You can't leave out the SS, you can't have N before E, and there must be the same
           number of Es and Ns.

           There are two other special formats:

                form => 'TRAD' is equivalent to form => 'SS EEE NNN'
                form => 'GPS'  is equivalent to form => 'SS EEEEE NNNNN'

           In a list context, this option means that the individual components are returned
           appropriately truncated as shown.  So with "SS EEE NNN" you get back "('SU', 387,
           147)" and not "('SU', 387.10908, 147.92248)".  The format can be given as upper case
           or lower case or a mixture.  If you want just the local easting and northing without
           the grid square, get the individual parts in a list context and format them yourself:

               my $gr = sprintf('Grid ref %2$s %3$s on Sheet %4$s', format_grid_landranger($e, $n))
               # returns: Grid ref 387 147 on Sheet 196

       maps
           Controls whether to include a list of map sheets after the grid reference.  Set it to
           1 (or any true value) to include the list, and to 0 (or any false value) to leave it
           out.  The default is "maps => 0".

           In a scalar context you get back a string like this:

               SU 387 147 on A:196, B:OL22E, C:180

           In a list context you get back a list like this:

               ('SU', 387, 147, A:196, B:OL22E, C:180)

       series
           This option is only used when "maps" is true.  It controls which series of maps to
           include in the list of sheets.  Currently the series included are:

           "A" : OS Landranger 1:50000 maps

           "B" : OS Explorer 1:25000 maps (some of these are designated as `Outdoor Leisure'
           maps)

           "C" : OS Seventh Series One-Inch 1:63360 maps

           "H" : Harvey British Mountain maps - mainly at 1:40000

           "J" : Harvey Super Walker maps - mainly at 1:25000

           so if you only want Explorer maps use: "series => 'B'", and if you want only Explorers
           and Landrangers use: "series => 'AB'", and so on.

           Note that the numbers returned for the Harvey maps have been invented for the purposes
           of this module.  They do not appear on the maps themselves; instead the maps have
           titles.  You can use the numbers returned as an index to the data in
           Geo::Coordinates::OSGB::Maps to find the appropriate title.

   "format_grid_trad(e,n)"
       Equivalent to "format_grid(e,n, { form => 'trad' })".

   "format_grid_GPS(e,n)"
       Equivalent to "format_grid(e,n, { form => 'gps' })".

   "format_grid_map(e,n)"
       Equivalent to "format_grid(e,n, { maps => 1 })".

   "format_grid_landranger(e,n)"
       Equivalent to

          format_grid(e,n,{ form => 'ss eee nnn', maps => 1, series => 'A' })

       except that the leading "A:" will be stripped from any sheet names returned, and you get a
       slightly fancier set of phrases in a scalar context depending on how many map numbers are
       in the list of sheets.

   "parse_grid"
       The "parse_grid" routine extracts a (easting, northing) pair from a string, or a list of
       arguments, representing a grid reference.  The pair returned are in units of metres from
       the false origin of the grid, so that you can pass them to "format_grid" or "grid_to_ll".

       The arguments should be in one of the following forms

       •   A single string representing a grid reference

             String                        ->  interpreted as
             --------------------------------------------------
             parse_grid("TA 123 678")      ->  (512300, 467800)
             parse_grid("TA 12345 67890")  ->  (512345, 467890)

           The spaces are optional in all cases.  You can also refer to a 100km square as "TA"
           which will return "(500000,400000)", a 10km square as "TA16" which will return
           "(510000, 460000)", or to a kilometre square as "TA1267" which gives "(512000,
           467000)".  For completeness you can also use "TA 1234 6789" to refer to a decametre
           square "(512340, 467890)" but you might struggle to find a use for that one.

       •   A list representing a grid reference

             List                             ->  interpreted as
             -----------------------------------------------------
             parse_grid('TA', 0, 0)           ->  (500000, 400000)
             parse_grid('TA', 123, 678)       ->  (512300, 467800)
             parse_grid('TA', 12345, 67890)   ->  (512345, 467890)
             parse_grid('TA', '123 678')      ->  (512300, 467800)
             parse_grid('TA', '12345 67890')  ->  (512345, 467890)

           If you are processing grid references from some external data source beware that if
           you use a list with bare numbers you may lose any leading zeros for grid references
           close to the SW corner of a grid square.  This can lead to some ambiguity.  Either
           make the numbers into strings to preserve the leading digits or supply a hash of
           options as a fourth argument with the `figs' option to define how many figures are
           supposed to be in each easting and northing.  Like this:

             List                                     ->  interpreted as
             -------------------------------------------------------------
             parse_grid('TA', 123, 8)                 ->  (512300, 400800)
             parse_grid('TA', 123, 8, { figs => 5 })  ->  (500123, 400008)

           The default setting of figs is 3, which assumes you are using hectometres as in a
           traditional grid reference.

       •   A string or list representing a map sheet and a grid reference on that sheet

                Map input                      ->  interpreted as
                ----------------------------------------------------
                parse_grid('A:164/352194')     ->  (435200, 219400)
                parse_grid('B:OL43E/914701')   ->  (391400, 570100)
                parse_grid('B:OL43E 914 701')  ->  (391400, 570100)
                parse_grid('B:OL43E','914701') ->  (391400, 570100)
                parse_grid('B:OL43E',914,701)  ->  (391400, 570100)

           Again spaces are optional, but you need some non-digit between the map identifier and
           the grid reference.  There are also some constraints: the map identifier must be one
           defined in Geo::Coordinates::OSGB::Maps; and the following grid reference must
           actually be on the given sheet.  Note also that you need to supply a specific sheet
           for a map that has more than one.  The given example would fail if the map was given
           as `B:OL43', since that map has two sheets: `B:OL43E' and `B:OL43W'.

           If you give the identifier as just a number, it's assumed that you wanted a Landranger
           map;

                parse_grid('176/224711')  ->  (522400, 171100)
                parse_grid(164,513,62)    ->  (451300, 206200)

           The routine will croak of you pass it a sheet identifier that is not defined in
           Geo::Coordinates::OSGB::Maps.  It will also croak if the supplied easting and northing
           are not actually on the sheet.

           In earlier versions, the easting and northing arguments were optional, and you could
           leave them out to get just the SW corner of the sheet.  This functionality has been
           removed in this version, because it's not always obvious where the SW corner of a
           sheet is (for an example look at the inset on Landranger sheet 107).

           If you need access to the position of the sheets in this version, you should work
           directly with the data in Geo::Coordinates::OSGB::Maps.

   "parse_trad_grid(grid_ref)"
       This is included only for backward compatibility.  It is now just a synonym for
       "parse_grid".

   "parse_GPS_grid(grid_ref)"
       This is included only for backward compatibility.  It is now just a synonym for
       "parse_grid".

   "parse_landranger_grid(sheet, e, n)"
       This is included only for backward compatibility.  It is now just a synonym for
       "parse_grid".

   "parse_map_grid(sheet, e, n)"
       This is included only for backward compatibility.  It is now just a synonym for
       "parse_grid".

   "random_grid([sheet1, sheet2, ...])"
       Takes an optional list of map sheet identifiers, and returns a random easting and northing
       for some place covered by one of the maps.  There's no guarantee that the point will not
       be in the sea, but it will be within the bounding box of one of the maps and it should be
       within one of the areas covered by the OSTN02 data set.

       •   If you omit the list of sheets, then one of map sheets defined in
           Geo::Coordinates::OSGB::Maps will be picked at random.

       •   As a convenience whole numbers in the range 1..204 will be interpreted as Landranger
           sheets, as if you had written "A:1", "A:2", etc.

       •   Any sheet identifiers in the list that are not defined in Geo::Coordinates::OSGB::Maps
           will be (silently) ignored.

       •   The easting and northing are returned as meters from the grid origin, so that they are
           suitable for input to the "format_grid" routines.

EXAMPLES

         use Geo::Coordinates::OSGB::Grid
            qw/parse_grid
               format_grid
               format_grid_landranger/;

         # Get full coordinates in metres from GR
         my ($e,$n) = parse_grid('TQ 23451 09893');

         # Reading and writing grid references
         # Format full easting and northing into traditional formats
         my $gr1 = format_grid($e, $n);                              # "TQ 234 098"
         my $gr2 = format_grid($e, $n, { form => 'SSEEENNN' } );     # "TQ234098"
         my $gr3 = format_grid($e, $n, { form => 'SSEEEEENNNNN'} );  # "TQ 23451 09893"
         my $gr4 = format_grid($e, $n, { form => 'gps'} );           # "TQ 23451 09893"
         my $gr5 = format_grid_landranger($e, $n);# "TQ 234 098 on Landranger sheet 198"

         # or call in list context to get the individual parts
         my ($sq, $ee, $nn) = format_grid($e, $n); # ('TQ', 234, 98)

         # parse routines to convert from these formats to full e,n
         ($e,$n) = parse_grid('TQ 234 098');
         ($e,$n) = parse_grid('TQ234098'); # spaces optional
         ($e,$n) = parse_grid('TQ',234,98); # or even as a list
         ($e,$n) = parse_grid('TQ 23451 09893'); # as above..

         # You can also get grid refs from individual maps.
         # Sheet between 1..204; gre & grn must be 3 or 5 digits long
         ($e,$n) = parse_grid(176,123,994);
         # put leading zeros in quotes
         ($e,$n) = parse_grid(196,636,'024');

       For more examples of parsing and formatting look at the test files.

BUGS AND LIMITATIONS

       The useful area of these routines is confined to the British Isles, not including Ireland
       or the Channel Islands.  But very little range checking is done, so you can generate
       pseudo grid references for points that are some way outside this useful area.  The corners
       of this larger area run from 64.75N 32.33W (Iceland) to 65.8N 22.65E (Norway) to 44.5N
       11.8E (Venice) to 44N 19.5W (the Western Approaches).

DIAGNOSTICS

   Messages from "format_grid"
       In case of error "format_grid" will die with a message.  Possible messages are:

       •   Format ... was not recognized

           The format code you supplied with "{ form => ... }" did not match any of the expected
           patterns.

       •   Too far off the grid: ...

           The (easting, northing) pair you supplied are too far away from the OS grid to be
           formatted with a valid grid square letter combination.

   Messages from "parse_grid"
       In case of error "parse_grid" will die with one of the following messages:

       •   No easting or northing found

           This means you passed something more than a 2-letter grid square but there were no
           numbers found in the latter part of the string.

       •   Easting and northing have different lengths in ...

           The easting and northing you supply must have same length to avoid ambiguity.

       •   Too many digits in ...

           You have supplied more than 10 digits.

       •   Grid reference .... is not on sheet ...

           You can get this if you pass a map sheet identifier and a short grid ref, but the grid
           ref is not actually on that particular sheet.

       •   Failed to parse a grid reference from ...

           This is the catch all message issued if none of the patterns matches your input.

       If you get an expected result from any of these subroutines, please generate a test case
       to reproduce your result and get in touch to ask me about it.

CONFIGURATION AND ENVIRONMENT

       There is no configuration required either of these modules or your environment.  It should
       work on any recent version of Perl better than 5.8, on any platform.

DEPENDENCIES

       Perl 5.08 or better.

INCOMPATIBILITIES

       None known.

LICENSE AND COPYRIGHT

       Copyright (C) 2002-2016 Toby Thurston

       OSTN02 transformation data included in this module is freely available from the Ordnance
       Survey but remains Crown Copyright (C) 2002

       This program is free software; you can redistribute it and/or modify it under the terms of
       the GNU General Public License as published by the Free Software Foundation; either
       version 2 of the License, or (at your option) any later version.

       This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
       without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
       See the GNU General Public License for more details.

       You should have received a copy of the GNU General Public License along with this program;
       if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
       Boston, MA 02110-1301 USA.

AUTHOR

       Toby Thurston -- 16 Feb 2016

       toby@cpan.org

SEE ALSO

       See Geo::Coordinates::OSGB.