Changes between Initial Version and Version 1 of Ticket #1232, comment 9


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Timestamp:
08/13/14 00:45:01 (5 years ago)
Author:
nezmi
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  • Ticket #1232, comment 9

    initial v1  
    5151> However, there may be cases in which the vehicle actually does leave the route – thus we need to avoid overcompensating and sticking to a route that the vehicle has left long since. Here I'd go for the modified snap logic I had proposed in #1093: when the vehicle is somewhere between two roads, give the route a greater weight than other nearby roads. (Maybe even make that weight dynamic: high at the beginning and decreasing if the position continues to be far away from the route).
    5252
    53 I recently drove with ''navit'' through an Austrian village, which had an incredibly tight road network. It was situated between high mountains, so the GPS HDOP was bad (15-20). ''navit'' was happily jumping the "vehicle" all over the place, even positioning it several streets away. This experience is the background of my suggestion (and I'm convinced your approach would have failed in that environment).
     53I recently drove with ''navit'' through an Austrian village (Vils), which had an incredibly tight road network. It was situated between high mountains, so the GPS HDOP was bad (15-20). ''navit'' was happily jumping the "vehicle" all over the place, even positioning it several streets away. This experience is the background of my suggestion (and I'm convinced your approach would have failed in that environment).
    5454
    5555Let me lay out the approach in more detail:
    5656
    57 The snap radius is computed as HDOP × !DevicePrecision
     57The snap radius is computed¹ as HDOP × !DevicePrecision
    5858!DevicePrecision is a configurable parameter, 6m would be a good consumer device ...
    5959One should add a small safety margin to the !DevicePrecision to avoid flapping, let's say
     
    8888
    8989You are the expert here -- perhaps the Kalman filter mentioned by Rainer Dorsch can calibrate the INS readings via the GPS readings, and thus solve the problem of the unknown device orientation. Of course this calibration is moot, if the device is moved within the vehicle, because it is hold manually or the suction cup drops from the screen ...
     90
     91
     92----
     93[¹] Well, to be more precise:
     94HDOP_of_last_valid_GPS_reading × !DevicePrecision + Simulated_Movement_since_last_valid_GPS_reading
     95
     96If the GPS position '''leaves''' the route, we have a current reading and simulated movement is Zero (so the simplification above was OK).
     97
     98Now have a short look what happens, if GPS position is '''lost''':
     99* Assume we enter a tunnel with 80 km/h, the HDOP of the last GPS reading was 5:
     100  * An audible warning will be given when exceeding Threshold1
     101  * This happens after 7.5 seconds ((200m - 5×7m)/80 km/h)
     102  * simulation will quit or switch to interactive mode when exceeding Threshold2
     103  * assuming Threshold2=1km and no INS support, this will happen after 43,5 seconds (actually to early for many tunnels I know, perhaps a configurable time threshold would be better? E.g. without INS support this would cover 4km: Simulation critical if it runs >3 minutes and position uncertainty exceeds Threshhold2?)
     104* Now assume a situation like in the Austrian village: degraded GPS (HDOP 20), low speed (30-50km/h):
     105  * Threshold1 is exceeded and warning sounded after 5.4 seconds ((200m - 20×7)/40 km/h)
     106  * simulation is considered uncritical for around 77 seconds (or with 3 min time threshold after 1860m)
     107* You are hiking within a dense forest, GPS degrades because of foliage to HDOP 20 before dropping out, your speed is 6 km/h
     108  * warning would be sounded after 36 seconds (perhaps somewhat late and suggesting the parameters should be vehicle specific ...)
     109  * simulation is considered uncritical for around 8.5 minutes (actually when hiking, user interaction is acceptable and should happen much earlier ... -> parameters should be vehicle specific)
     110
     111Handling extended simulation will need some consideration and practical experiments ...