Tunnel Extrapolation

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Tunnel extrapolation is an extrapolation function which calculates with the last available speed information before the loss of the gps signal if a tunnel flag is set within your openstreetmaps map.

how to use

To use tunnel extrapolation you need to patch osm.c with the follow content:

Just save this patch as osm.diff, go the the navit folder, enter "patch -p0 < osm.diff" and compile navit svn. If you have already added a different patch to osm.c ( e.g. tryagain's ticket #859), the lines are probably relocated. Change the patch's line information or just copy those three lines at the right place.

Index: osm.c
--- osm.c       (Revision 4536)
+++ osm.c       (Arbeitskopie)
@@ -1019,6 +1019,9 @@
               flags[access_value(v)] |= AF_DANGEROUS_GOODS;
+       if (! strcmp(k,"tunnel") && !strcmp(v,"1")) {
+               flags[0] |= AF_UNDERGROUND;
+       }
     if (! strcmp(k,"note"))
 if (! strcmp(k,"name")) {

Also, you need to add "tunnel_extrapolation="12"" to <tracking ...>. You may need to lower this value, if the cursor runs ahead your position or vice versa, if it lags behind you. 12 stands for 1.2s extrapolation per gps rate.

Note, that this will only work if you processed your own maps with maptool and the tunnel is yet marked as one in openstreetmap as well (it's not? Well, go ahead!)! This article is going to help you to get your own map: http://wiki.navit-project.org/index.php/OpenStreetMap#From_.bz2

This feature will be added to svn if it has been tested with success.