Mapping Hacks

Work with Different Coordinate Systems #26

Chapter 3, Mapping Your World

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HACK

Converting Lat/Long to Lat/Long in Perl

If you need more fine-grained control over the conversion, you’ll probably

want to use a program, rather than calculating by hand or using PROJ.4.

Walt Mankowski has written the CPAN module

Geo::Coordinates::

DecimalDegrees

, which takes care of the details. Assuming you have a stan-

dard Perl installation, you should be able to install it with this command:

perl -MCPAN -e 'install Geo::Coordinates::DecimalDegrees'

Here is a bit of Perl to illustrate the use of this module on the same parking

lot latitude:

#!/usr/bin/perl

use Geo::Coordinates::DecimalDegrees;

my ($deg, $min, $sec) = @ARGV;

print "$deg $min' $sec\"\tDMS\n";

my $decimal_degrees = dms2decimal($deg, $min, $sec);

print "$decimal_degrees\tDecimal degrees\n";

($deg, $min, $sec) = decimal2dms($decimal_degrees);

print "$deg $min' $sec\"\tBack to DMS\n";

($deg, $min) = decimal2dm($decimal_degrees);

print "$deg $min'\tDegrees + decimal minutes\n";

Put this sample code in a file called decimal.pl and execute it to yield the fol-

lowing output:

$ perl decimal.pl 38 24 57

38 24' 57" DMS

38.4158333333333 Decimal degrees

38 24' 56.9999999999941" Back to DMS

38 24.9499999999999' Degrees-decimal minutes

Note that rounding causes some loss of accuracy.

HACK

#26

Work with Different Coordinate Systems Hack #26

Your GPS gives you latitude and longitude, ...