XPost: rec.arts.sf.written, rec.arts.sf.science   
   From: rod.speed.aaa@gmail.com   
      
   Greg Goss  wrote   
   > Dimensional Traveler  wrote   
      
   >> There are all kinds of problems with GPS based directions systems   
   >> and software.  IME almost always because the map is wrong.  I've   
   >> run into I don't know how many cases of the directions suddenly   
   >> becoming effectively gibberish because the actual road was 50   
   >> feet off to one side of where the map thinks it is and thinks you   
   >> are either driving thru buildings or cross country across the desert.   
      
   > There is a large chunk of rural southern Alberta where both of our   
   > GPSs thought we were about a half mile east of where we really were.   
   > One of them "adjusted" us to the nearest rural road, while the other   
   > just had us driving through the canola.   
      
   > I assume that both GPSs bought the map from some supplier with   
   > defective placement of that rather large chunk of my province.  And   
   > that prior to GPSs, the supplier never noticed the misalignment of a   
   > big chunk of map.   
      
   > Between Alberta and BC are several mountain ranges.  Driving in narrow   
   > canyons, you have a view of a limited number of satellites, and the   
   > signal from those few can bounce off cliffs and give false readings.   
      
   No, that isnt what happens. What happens is that the narrow canyon   
   restricts the number of satellites that are visible to your system and   
   that's what reduces the accuracy of the fix.   
      
   > I fairly often get directions from some minor trail across the   
   > river to try to get me back onto the highway I'm still on.   
      
   >> The worst instance I've experienced the difference between map   
   >> and reality was about two miles (one of the SW desert states).   
      
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