[Ovmsdev] SIM808 GPS float bug

Michael Balzer dexter at expeedo.de
Tue Jan 24 01:49:18 HKT 2017

Hi Edward,

welcome :)

I do notice some offset from road maps once in a while. So go ahead
optimizing gps2latlon(), maybe that's the offset source.

The atof() function should be fixed regardless of the GPS conversion,
I'll take care of that.


Am 23.01.2017 um 08:12 schrieb Edward Cheeseman:
> Hello,
> I am new to OVMS. I have a Gen2 Leaf on Dexters server. Tom has helped
> me set it up.
> I found my GPS data was off up to two degrees. I’ve traced it to
> myatof() in utils.c.
> It adds the fractional part with both positive and negative numbers,
> where it should subtract for negative numbers.
> myatof() is used in SIM808 lat and long conversions, and somewhere in
> Twizy which I didn’t look into.
> I suppose there isn’t that many SIM808 based OVMSs in the Southern or
> Western hemispheres?
> It is easy to fix, but maybe going through float in the first place
> isn’t necessary?
> Looks like there is 31bits of information coming out of the GPS where
> float will drop this to 23bits.
> I’ve started rewriting gps2latlon() to use a long long (64bit) integer
> multiply and divide.
> I see reference to SIM808 and 908 on an arduino shield, so I might
> have a look to see what they have done.
> Edward
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Michael Balzer * Helkenberger Weg 9 * D-58256 Ennepetal
Fon 02333 / 833 5735 * Handy 0176 / 206 989 26

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