Mapping Hacks

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Chapter 6, Mapping on Your Desktop

#71 Turn Your Tracklogs into ESRI Shapefiles

HACK

As you can see, the gpstrans output format is very simple. There’s a header

line with some metadata, followed by several lines of data, each containing

four tab-separated fields: the data type (i.e.,

T for tracklog), the timestamp,

and a latitude/longitude pair. Obviously, the output from other GPS data

download programs will look different, but the principle is the same.

Extending the following code to work with the output of GARNIX and

other programs is left as an exercise for the reader.

On the Mapping Hacks web site, you’ll find a GPX-based

version of track2shp.pl under http://mappinghacks.com/code/.

The Code

#!/usr/bin/perl

use Geo::Shapelib;

use Time::Piece;

use constant TIME_THRESHOLD => 10; # minutes

use constant TIME_FORMAT => "%m/%d/%Y %H:%M:%S";

use strict;

use warnings;

my ($in, $out) = @ARGV;

die "Usage: $0 \n" unless $in and $out;

my $shp = new Geo::Shapelib;

$shp->{Name} = $out;

$shp->{Shapetype} = 3; # PolyLine, according to Geo::Shapelib source

$shp->{FieldNames} = ['ID', 'Date'];

$shp->{FieldTypes} = ['Integer', 'String:16'];

open TRACK, "<", $in or die "Can't open $in: $!";

my $id = 0;

my (@vertices, $previous);

sub add_shape {

return unless @vertices > 2;

push @{$shp->{Shapes}}, {

SHPType => 3, # PolyLine

ShapeId => $id,

NVertices => scalar @vertices,

Vertices => [@vertices]

};

push @{$shp->{ShapeRecords}}, ...