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March 20, 2005

Google Maps GPS GPX Waypoint Extractor

Category: GPS,Software — badsegue @ 1:17 am

background

I previously wrote about how to extract waypoints and create a GPX file from MSN Yellow Pages using a bookmarklet. This article explains how to do the same thing for Google Maps. I use mine to supplement the points of interest (POIs) in North American CitySelect v5 for my Garmin 76C.

POI coverage can be spotty, even in well established and stable cities. In newly developed or more remote areas there may be nothing at all. Online directories should have just about every business that would appear in the Yellow Pages, and are much more timely than the software releases. By tapping these online resources you can have the most accurate and complete set business POIs possible.

approach

This can be done relatively easily because of the way the search results are contained on a single place with the relevant data unencoded. Yahoo and most of the other online providers lack this ease of access. Even Google Local doesn’t put all the information on a single page, you’d have to drill down into each returned place to get the coordinates.

implementation

The code looks like this:

javascript:
(function(){
  var t=document.getElementById('vp').
        contentDocument.getElementsByTagName('SCRIPT').item(0).text;
  var pts=t.match(/<point .*?<\/title>/g);
  var doc=open().document;
  var bod=doc.body;
  doc.write('<textarea rows=%2250%22 cols=%22100%22>');
  doc.write('\n<gpx xmlns=%22http://www.topografix.com/GPX/1/1%22 
             creator=%22gpxextr%22 version=%221.1%22 

             xmlns:xsi=%22http://www.w3.org/2001/XMLSchema-instance%22>');
  for(i=0;i<pts.length;i++){
    var latlon = pts[i].match(/(-?\d{2}\.\d{6}).*?(-?\d{2}\.\d{6})
    .*?title.*?>(.*?)<\/title>/);
    latlon[3] = latlon[3].replace(/<.*?>/g, '');
    doc.write('\n<wpt lat=%22', latlon[1], '%22 lon=%22', latlon[2],
    '%22>\n<name>', latlon[3], '</name>\n</wpt>');
  }
  doc.write('\n</gpx></textarea>');
  doc.close();
}
)()

The Google Maps GPX Waypoint Extractor link (Firefox only) will run a little Javascript bookmarklet that parses the interesting parts of the map link and write them as a GPX file into a new browser window. (The MSN and Google extractors only works in Firefox/Mozilla for now. IE limits the the length of a bookmark and right now it’s too long. There’s a way around this but it requires putting the code into a file and having the bookmarklet ‘inject’ it into the page. I haven’t got that working yet though.)

If you click on the link, the script won’t find anything on this page. Add the link (right-click and add it, or drag the link to your toolbar) then open Google Maps and do a search for “Pizza Duck,NC”. Now select the GPS GPX Extractor bookmark and you should get waypoints for all the results on the page. You should be able to import that file into most software that manages waypoints.

etc…

MSN Yellow Pages and Google Maps are the only sites I know of that have easily parsed coordinates. I think Google Local searches can be tapped as well, but it would require fetching each detail page. There are online GIS sources that can be used to get other types of waypoints, like parks and such. If you know of other sources of information that can be extracted like this, let me know.

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1 Comment

  1. [...] background Previously we showed how to pull GPS waypoints from MSN Yellow Pages and Google Maps results using a Firefox bookmarklet. Now this can be done [...]

    Pingback by badsegue.org : a journal of creative computing»Blog Archive » Google and MSN GPX GPS Waypoint Extraction — April 4, 2005 @ 9:09 am

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