NAME
Geo::Proj4 - PROJ cartographic projections library
INHERITANCE
Geo::Proj4
is a DynaLoader
SYNOPSIS
use Geo::Proj4;
my $proj = Geo::Proj4->new(proj => "merc",
ellps => "clrk66", lon_0 => -96)
or die "parameter error: ".Geo::Proj4->error. "\n";
my $proj = Geo::Proj4->new(" proj=merc ellps=clrk66 lon_0=-96")
or die "parameter error: ".Geo::Proj4->error. "\n";
my $proj = Geo::Proj4->new(init => "epsg:28992");
my ($x, $y) = $proj->forward($lat, $lon);
if($proj->hasInverse)
{ my ($lat, $lon) = $proj->inverse($x, $y);
...
}
my $proj = Geo::Proj4->new(init => "epsg:26985") or die;
my ($lat, $lon) = $proj->inverse(401717.80, 130013.88);
my $point = [ 123.12, -5.4 ];
my $projected_point = $from->transform($to, $point);
my $projected_multi = $from->transform($to, \@points);
DESCRIPTION
DEPRECATED: after a stable period of about 25 years under "version 4", this library has seen huge changes since 2018. The changes are too structural to adapt this module to match them. You can still manually install this module with the '4' version with some effort: see wiki in git. I have no time or use to create a new module. Sorry.
The Open Source PROJ library converts between geographic coordinate systems. It is able to convert between geodetic latitude and longitude (LL, most commonly the WGS84 projection), into an enormous variety of other cartographic projections (XY, usually UTM).
WARNING: It is not always clear what the source projection is when forward() or inverse() are used, i.e. in what projection system the source data is expected to be in. Therefore, you can better be specific on both source and destination projection and use transform().
Version '4' of this library existed that long that it became part of its domain name https://proj4.org and this module. However, in 2018 it moved to version '5', and 2019 saw version '6'. Also those versions are supported by this module.
METHODS
Instantiation
- Geo::Proj4->new($string|%options)
-
The object defines the target projection, but that's easier said than done: projections have different parameter needs. The parameters which can (or need to) be used are listed with
cs2cs -lP
. The manual page ofcs2cs
explains how the configuration works.Two ways are provided to define the projection. Either, use a list of %options, which are pairs of parameters, or pass one string which contains all parameters at once. You must supply a
proj
parameter.In case of an OPTION list: WARNING: Specify boolean parameters (e.g. the south parameter to the UTM projection) with a matching value of undef.
example:
my $proj = Geo::Proj4->new(proj => "merc", ellps => "clrk66", lon_0 => -96 ) or die Geo::Proj4->error; my $proj = Geo::Proj4->new(" proj=merc ellps=clrk66 lon_0=096") or die Geo::Proj4->error; my $proj = Geo::Proj4->new(init => "epsg:$epsg");
Accessors
- $obj->datum()
-
Tries to return a datum name for this projection.
- $obj->dump()
-
Write the definition in extended form to stdout. This output cannot be caught, because it is done on stdio level, below the reach of PerlIO.
- Geo::Proj4->error()
-
Returns a dualvar (see Scalar::Util) containing the error number and error string of the last reported error.
example:
my $proj = Geo::Proj4->new(...); unless(defined $proj) { my $error = Geo::Proj4->error; warn "error-code: ".$error 0; warn "error-string: $error\n"; }
- $obj->hasInverse()
-
Returns whether the reverse function for the projection exists. Some projections are one-way.
- $obj->isGeocentric()
-
Returns true when the source projection is using a geocentric coordinate system; i.e. uses x-y coordinates.
- $obj->isGeodesic()
-
Returns true when the source projection is using a geodetic coordinate system; i.e. uses lat long coordinates. Same as isLatlong()
- $obj->isLatlong()
-
Returns true when the source projection is using a geodetic coordinate system; i.e. uses lat long coordinates. Same as isGeodesic().
- $obj->normalized()
-
Returns a string which is produced by the library based on the data extracted from the initiation parameters. This string may be more explicit than the passed values, and could be used for debugging.
- $obj->projection()
-
Returns the projection type.
Converters
- $obj->forward($latitude, $longitude)
-
Perform a forward projection from $latitude and $longitude (LL) to the cartographic projection (XY) represented by the Geo::Proj4 instance.
WARNING: for historic reasons, latitude and longitude are assumed to be in (floating point) degrees, although the library expects rads. See forwardRad(). A latitude South of the Equator or a longitude West of the Prime Meridian will give negative values.
Returned are two values, usually X and Y in meters, or whatever units are relevant to the given projection. When the destination projection also is geodetic, than the order of parameters will be returned as LONG,LAT (not lat,long!)
On error,
forward
will return undef for both values.example:
my ($x, $y) = $proj->forward($lat, $lon); my ($long2, $lat2) = $proj->forward($lat, $lon);
- $obj->forwardRad($latitude, $longitude)
-
Perform a forward projection from $latitude and $longitude (LL) to the cartographic projection (XY) represented by the Geo::Proj4 instance. This function reflects to library function
forward()
, expecting radians, not degrees. - $obj->inverse(($x,$y) | ($lat,$long))
-
Perform an inverse projection from the (cartographic or geodetic) projection represented by this Geo::Proj4 object, back into latitude and longitude values.
WARNING: for historic reasons, latitude and longitude are assumed to be in (floating point) degrees, although the library expects rads. See inverseRad().
On error,
inverse
will return undef for both values.example:
if($proj->hasInverse) { my ($lat, $lon) = $proj->inverse($x, $y); ... }
- $obj->inverseRad(($x,$y) | ($lat|$long))
-
Perform an inverse projection from the (cartographic) projection represented by this Geo::Proj4 object, back into latitude and longitude values. Latitude and longitude are assumed to be in radians. See inverse().
- $obj->transform($to, $point|ARRAY-of-$points)
-
Translate the $points into the projecten of $to. Each point is specified as two or three values in an ARRAY. In case of latlong source or destination projections, coordinates are translated into radians and/or back. Both input and output values are always in X-Y/LongLat order. See transformRad()
example:
my $from = Geo::Proj4->new(" proj=latlong datum=NAD83"); my $to = Geo::Proj4->new(" proj=utm zone=10 datum=WGS84"); my $point = [ 1.12, 3.25 ]; # See Geo::Point my $pr_point = $from->transform($to, $point); my $pr = $from->transform($to, [ $point1, $point2 ]); my $pr_point1 = $pr->[0]; my $pr_point2 = $pr->[1];
- $obj->transformRad($to, $point|ARRAY-of-$points)
-
Translate the $points into the projecten of $to. Each point is specified as two or three values in an ARRAY. In case of latlong source or destination projections, coordinates are expected to be in radians. Both input and output values are always in X-Y/LongLat order. See transform()
Library introspection
- Geo::Proj4->datumInfo($label)
-
Returns a hash with information about the specified datum. With listDatums(), all defined LABELS can be found.
- Geo::Proj4->ellipsoidInfo($label)
-
Returns a hash with information about the specified ellipsis. With listEllipsoids(), all defined LABELS can be found.
- $obj->libVersion()
- Geo::Proj4->libVersion()
-
Returns the version of the proj4 library.
- Geo::Proj4->listDatums()
-
Returns a list with all defined datum labels.
example:
foreach my $id (Geo::Proj4->listDatums) { my $def = Geo::Proj4->datum($id); print "$id = $def->{ellips_id}\n"; }
- Geo::Proj4->listEllipsoids()
-
Returns a list with all defined ellips labels.
example:
foreach my $id (Geo::Proj4->listEllipsoids) { my $def = Geo::Proj4->ellipsoid($id); print "$id = $def->{name}\n"; }
- Geo::Proj4->listTypes()
-
Returns a list with all defined projection types.
example:
foreach my $id (Geo::Proj4->listTypes) { my $def = Geo::Proj4->type($id); print "$id = $def->{description}\n"; }
- Geo::Proj4->listUnits()
-
Returns a list with all defined unit labels.
example:
foreach my $id (Geo::Proj4->listUnits) { my $def = Geo::Proj4->unit($id); print "$id = $def->{name}\n"; }
- Geo::Proj4->typeInfo($label)
-
Returns a hash with information about the specified projection type. With listTypes(), all defined LABELS can be found.
- Geo::Proj4->unitInfo($label)
-
Returns a hash with information about the specified unit. With listUnits(), all defined LABELS can be found.
DETAILS
Install
Geo::Proj4 uses XS to wrap the PROJ.4 cartographic projections library. You will need to have the PROJ.4 library installed in order to build and use this module. You can get source code and binaries for the PROJ.4 library from its home page at http://proj4.org.
Projections
Covering all the possible projections and their arguments in PROJ.4 is well beyond the scope of this document. However, the cs2cs(1)
utility that ships with PROJ.4 will list the projections it knows about by running cs2cs -lp, the ellipsoid models it knows with the -le parameter, the units it knows about with -lu, and the geodetic datums it knows with -ld. Read cs2cs(1) for more details.
Alternately, you can read the PROJ.4 documentation, which can be found on the project's homepage. There are links to PDFs, text documentation, a FAQ, and more.
Bugs
One common source of errors is that latitude and longitude are swapped: some projection systems use lat-long, other use x-y which is a swapped order. Especially the forward() and inverse() cause this problem, always flipping the coordinate order. The transform() method is much easier: input and output in x-y/long-lat order.
Also be warned that the values must have the right sign. Make sure you give negative values for south latitude and west longitude. For calculating projections, this is more important than on maps.
DIAGNOSTICS
REFERENCES
See the Geo::Point website at http://perl.overmeer.net/geo/ for an html version of this and related modules;
Effusive thanks to Frank Warmerdam (maintainer of PROJ.4) and Gerald Evenden (main contributor of PROJ.4). Their PROJ.4 library home page: http://proj4.org
proj(1), cs2cs(1), pj_init(3).
COPYRIGHTS
Developed and maintained by Mark Overmeer <[email protected]>. Copyright (c) 2004-2018 by the authors. All rights reserved.
Originally Written by Schuyler Erle <[email protected]> and Rich Gibson <[email protected]>. Their site: Mapping Hacks home page: http://www.mappinghacks.com
LICENSE
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.