Tunnel Extrapolation

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Revision as of 08:38, 10 July 2011 by Korrosa (talk | contribs) (Tidy. Perhaps we should make a patch for this?)
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Tunnel extrapolation is an extrapolation function which uses the last available speed data to extrapolate the position of your vehicle inside a tunnel.

How to Use

To use tunnel extrapolation you need to patch navit/navit/maptool/osm.c by copying the three highlighted lines at the right place:

	  if (! strcmp(k,"hazmat")) {
	   	 flags[access_value(v)] |= AF_DANGEROUS_GOODS;
		 level=5;
 	  }
          if (! strcmp(k,"tunnel") && ! strcmp(v,"1")) {
                  flags[0] |= AF_UNDERGROUND;
          }
	  if (! strcmp(k,"note"))
		  level=5;
	  if (! strcmp(k,"name")) {
		  attr_strings_save(attr_string_label, v); 
		  level=5;

navit/navit/track.c needs to be edited too:

         if (!vehicle_get_attr(tr->vehicle, attr_position_valid, &valid, NULL))
             valid.u.num=attr_position_valid_valid;
  #if 0
         if (valid.u.num == attr_position_valid_invalid) {
             tr->valid=valid.u.num;
         return 0;
         }
 #endif
         if (!vehicle_get_attr(tr->vehicle, attr_position_speed, &speed_attr, NULL) ||


Also, you need to add tunnel_extrapolation="12" to <tracking ... >. You will need to play around with this value if you find that the cursor lags or runs ahead of your actual position. 12 stands for 1.2s extrapolation per gps rate.


Note that this function will only work if you process your own maps with maptool, and the particular section of highway has the tunnel=yes key/value pair in OSM (and if it hasn't, go ahead and add it!). To process your own map, see OpenStreetMap#From_.bz2


This feature will become permanent after successful testing.