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Sunday August 29, 2004
03:37 PM

Perl and the Magellan GPS Companion

[ #20627 ]

I have the Magellan GPS Companion, which is a Springboard module for my Visor Edge (but really any Palm thingy).

I've been having a bit of fun taking it around Chicago, and even on trips. Now I have a bunch of waypoints, but until last night they were stuck on my Visor. The software lets me beam waypoints, presumably to other thingys with the same module, but I don't see any way to export them to something like text.

No matter. Perl can do it just fine. I started with the Palm::PDB module, wrote my own concrete class for the factory, and shazam!: Palm::Magellan::NavCompanion. It's a developer's release right now, but you should be able to access your waypoints even if the module is a bit ugly and incomplete. It should make its way around CPAN in a day or so.

    use Palm::Magellan::NavCompanion;
    my $pdb = Palm::Magellan::NavCompanion->new;
    $pdb->Load( $file );
    my $waypoints = $pdb->{records};
    $, = ", ";
    foreach my $wp ( @$waypoints )
        print $wp->name, $wp->latitude, $wp->longitude;
        print "\n";

I can only read the file right now. I need to reverse engineer some more bits before I figure out how to write things back out.

Interesting tech note: a lot of the things in the database format as C strings, so they end in a null byte. I thought that I could handle that with some "x" placeholders in unpack, but I kept getting errors like "x outside of string". Apparently it can't figure out the null byte positions on its own. I punted and read the strings as one chunk then split on the null bytes.

I know the maximum length of the strings (because the GUI won't let me enter more characters than that), so I should be able to use the Z format specifier, but I didn't get around to trying that. When I don't have much time, I use stuff I know will work. I can refactor later.

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