[Ovmsdev] GPS flatbed alerts from military jamming/spoofing?

Michael Balzer dexter at expeedo.de
Fri Apr 29 21:59:09 HKT 2022


I've just pushed an attempt to fix the false alerts by introducing and 
applying a normalized GPS "signal quality" level from the satellite 
count and HDOP.

 From analysis of my collected GPS data I've come to the conclusion the 
HDOP isn't a reliable standlone indicator. I've seen coordinates off by 
8 kilometers with HDOP at 1.5, which should normally mean "nearly 
perfect". Only by taking also the satellite count into account, all 
false position readings could be filtered.


    GPS: add normalized signal quality level, add web UI live status info
    Location: flatbed movement alarm only with reliable positioning

       New metrics:
         v.p.gpssq                           -- GPS signal quality [%]
    (<30 unusable, >50 good, >80 excellent)
         v.p.gpstime                         -- Time (UTC) of GPS
    coordinates [Seconds]

       New configs:
         [vehicle] gps.sq.good               -- SQ level for location
    state "reliable", default 60
         [vehicle] gps.sq.bad                -- SQ level for location
    state "unreliable", default 40

       New events:
         gps.sq.good                         -- GPS position is now reliable
         gps.sq.bad                          -- GPS position is now

For the Teslas I've added a simple 0/100 setting, and a satellite count 
based calculation for the Jaguar. Btw, the Model S adaption seems to 
lack handling for losing the GPS lock, and the Jaguar iPace seems to 
lack setting the GPS lock at all.

The quality level replaces the GPS lock status role for the location 
module: no location changes or flatbed alerts will be emitted while 
quality is "bad".

The quality formula and thresholds work nicely for my region, please 
test & report if changes are necessary. I've added the quality level to 
the MP "L" message, so you can easily check your levels from a daily 
data export. It's also included in the live widget of the web UI's 
status page.


Am 02.04.22 um 21:30 schrieb Craig Leres:
> On 4/2/22 11:06, Michael Balzer wrote:
>> Your parking lot has pretty good GPS reception with never less than 7 
>> satellites in view, my case is near the edge of GPS unusability with 
>> some periods of only 2 satellites in view.
> My condo has a detached two car garage and the walls and tar & gravel 
> roof are fairly RF transparent. My dev unit is in the spare bedroom 
> and there is aluminum (or similar) in the walls and roof that does a 
> good job of blocking both gnss and siriusxm satellite radio so the 
> antenna (attached to window blinds) does not have a 360° view of the 
> sky. Essentially it can only see out the window (which I believe has a 
> UV coating that probably degrades the signal some amount.
>         Craig

Michael Balzer * Helkenberger Weg 9 * D-58256 Ennepetal
Fon 02333 / 833 5735 * Handy 0176 / 206 989 26

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