Tag Archives: map

map markers: don’t have to stick to the defaults

Some of the languages of Irian Jaya

Map background: Natural Earth (public domain)
Language point data: Glottolog (licence: Creative Commons — Attribution-ShareAlike 3.0 Unported — CC BY-SA 3.0)
Map markers: font: Overpass (licence: SIL OFL/LGPL), character: 💬 — U+1F4AC SPEECH BALLOON.
Label font: U001Con Italic (foundry: URW++, licence: AFPL)

Not really getting the Azimuthal Equidistant projection right

Update: thanks to André, this works! See the updated ogr2ogr line.

All I really wanted to do is make a map like this:

This is an Azimuthal Equidistant projection, with me at the centre (of course) and the rest of the world spread out in a fan by distance and bearing. It’s somewhat surprising to find that South Africa is almost directly east of Toronto, and New Zealand to the southwest.

If I had a directional antenna and a rotor, this map would show me where I would have to point the antenna to contact that part of the world. I can’t rotate my dipole (unless I commit some unauthorized local plate tectonics) so I’m stuck with where my antenna transmits and receives best.

The above map was made with AZ_PROJ, a PostScript program of some complexity for plotting world maps for radio use. The instructions for installing and running AZ_PROJ are complex and slightly dated. I got the above output running it through Ghostscript like this:

gs -sDEVICE=pdfwrite -sOutputFile=va3pid_world.pdf az_ini.ps -- az_proj.ps world.wdb

The format of the az_ini.ps file is complex, and I’m glad I’m an old PS hacker to be able to make head or tail of it.

For all its user-hostility, AZ_PROJ is powerful. Here’s a version of the map I wanted all along:

This shows my furthest QSO in each of the 16 compass directions. (You might note that North is empty: my furthest contact in that direction is some 13km away, whether by lack of folks in that sector or dodginess of my antenna.) Contrast that with my Mercator QSO map, and you’ll see that Azimuthal Equidistant is a much better projection for this application.

To show how radically different the world looks to different people, here’s the world according to my mate Rob in Hamilton, NZ:

I’d been trying to use OGR to transform arbitrary shapefiles into this projection. For maps entirely contained within the same hemisphere (so having extent less than ±90° in any cardinal direction), this works:

ogr2ogr -t_srs "+proj=aeqd  +lat_0=43.7308 +lon_0=-79.2647" out.shp in.shp

The lat_0 and lon_0 parameters are just where you want the centre of the map to be. Things get a bit odd if you try to plot the whole world:

The antipodes get plotted underneath, and everything looks messed up. I may have to take my question to GIS – Stack Exchange to see if I can find an answer. Still, for all its wrongness, you can make something pretty, like my whole world Maidenhead locator grid projected this way turns into a rose:

Update: André advised on Stack Exchange that you need to specify the correct radius:

ogr2ogr -t_srs "+proj=aeqd  +lat_0=43.7308 +lon_0=-79.2647 +R=6371000" va3pid-world.shp TM_WORLD_BORDERS_SIMPL-0.3.shp

This works rather well:

aeqd-qgis

 

 

Ham Radio log to interactive OpenStreetMap

You might notice that there’s now a Ham Radio QSO Map lurking on the front page. Thanks to the WordPress OpenStreetMap plugin (which I’ve slightly abused before). Here’s a small piece of Perl which will take your ADIF log and convert it to a WP-OSM marker file.

Note that this program assumes you’ve downloaded your log from QRZ.com, as it requires the locator field for both inbound and outbound stations.

#!/usr/bin/perl -w
# adif2osm - convert ADIF log to OSM map file
# scruss.com / VA3PID - 2011/06/19

use strict;
use constant MARKERDIR =>
  'http://glaikit.org/wp-content/plugins/osm/icons/';
use constant QRZURL => 'http://qrz.com/db/';
sub maidenhead2latlong;

my ( $temp, @results ) = '';

### Fast forward past header
while (<>) {
  last if m/<eoh>\s+$/i;
}

### While there are records remaining...
while (<>) {
  $temp .= $_;

  ### Process if end of record tag reached
  if (m/<eor>\s+$/i) {
    my %hash;
    $temp =~ s/\n//g;
    $temp =~ s/<eoh>.*//i;
    $temp =~ s/<eor>.*//i;
    my @arr = split( '<', $temp );
    foreach (@arr) {
      next if (/^$/);
      my ( $key, $val ) = split( '>', $_ );
      $key =~ s/:.*$//;
      $hash{ lc($key) } = $val unless ( $key eq '' );
    }
    push @results, \%hash;
    $temp = '';
  }
}

# generate OSM plugin file
my @data = ();
my ( $mygrid, $station_callsign ) = '';

# output header
print
  join( "\t", qw/lat lon title description icon iconSize iconOffset/ ),
  "\n";
foreach (@results) {
  next unless ( exists( $_->{gridsquare} ) && exists( $_->{call} ) );
  $mygrid = $_->{my_gridsquare}
    if ( exists( $_->{my_gridsquare} ) );
  $station_callsign = $_->{station_callsign}
    if ( exists( $_->{station_callsign} ) );

  push @data, $_->{freq} . ' MHz' if ( exists( $_->{freq} ) );
  $data[$#data] .= ' (' . $_->{band} . ')' if ( exists( $_->{band} ) );
  push @data, $_->{mode} if ( exists( $_->{mode} ) );
  push @data, $_->{qso_date} . ' ' . $_->{time_on} . 'Z'
    if ( exists( $_->{qso_date} ) && exists( $_->{time_on} ) );
  my ( $lat, $long ) = maidenhead2latlong( $_->{gridsquare} );
  print join( "\t",
    $lat,
    $long,
    '<a href="' . QRZURL . $_->{call} . '">' . $_->{call} . '</a>',
    join( ' - ', @data ),
    MARKERDIR . 'wpttemp-green.png',
    '0,-24' ),
    "\n";

  @data = ();
}

# show home station last, so it's on top
my ( $lat, $long ) = maidenhead2latlong($mygrid);
print join( "\t",
  $lat,
  $long,
  '<a href="'
    . QRZURL
    . $station_callsign . '">'
    . $station_callsign . '</a>',
  'Home Station',
  MARKERDIR . 'wpttemp-red.png',
  '0,-24' ),
  "\n";

exit;

sub maidenhead2latlong {

  # convert a Maidenhead Grid location (eg FN03ir)
  #  to decimal degrees
  # this code could be cleaner/shorter/clearer
  my @locator =
    split( //, uc(shift) );    # convert arg to upper case array
  my $lat      = 0;
  my $long     = 0;
  my $latdiv   = 0;
  my $longdiv  = 0;
  my @divisors = ( 72000, 36000, 7200, 3600, 300, 150 )
    ;                          # long,lat field size in seconds
  my $max = ( $#locator > $#divisors ) ? $#divisors : $#locator;

  for ( my $i = 0 ; $i <= $max ; $i++ ) {
    if ( int( $i / 2 ) % 2 ) {    # numeric
      if ( $i % 2 ) {             # lat
        $latdiv = $divisors[$i];    # save for later
        $lat += $locator[$i] * $latdiv;
      }
      else {                        # long
        $longdiv = $divisors[$i];
        $long += $locator[$i] * $longdiv;
      }
    }
    else {                          # alpha
      my $val = ord( $locator[$i] ) - ord('A');
      if ( $i % 2 ) {               # lat
        $latdiv = $divisors[$i];    # save for later
        $lat += $val * $latdiv;
      }
      else {                        # long
        $longdiv = $divisors[$i];
        $long += $val * $longdiv;
      }
    }
  }
  $lat  += ( $latdiv / 2 );         # location of centre of square
  $long += ( $longdiv / 2 );
  return ( ( $lat / 3600 ) - 90, ( $long / 3600 ) - 180 );
}

You’ll need to update MARKERDIR to reflect your own WP-OSM installation. Mine might move, so if you don’t change it, and you don’t get markers, please don’t blame me.

The basic code to include a map is like this:

You’ll need to change the marker_file URL, too.

Note that, while this script generates links into the QRZ callsign database, it doesn’t hit that site unless you click a link.

fallout from last night’s OSM 6th birthday Mappy Hour in Toronto

It was fun – there were geo-aware cupcakes!

In a moment of geek worlds colliding, Emma showed up, and now I have people clamouring for tablet at Mappy Hour. Sigh, those old ecommons links just don’t fade …