[Ovmsdev] SIM808/SIM908 GPS accuracy

[Edward Cheeseman]

Oh, can someone send me a DIAG capture (or confirm) that the SIM908 lat/long outputs are (D)DDMM.MMMM format, rather than (D)DDMM.MMMMMM?
I’m error checking so either will work, just don’t want to leave data behind :)

Edward

> On 2/02/2017, at 7:59 PM, Edward Cheeseman <cheesemanedward at gmail.com> wrote:
> 
> Hi Mark,
> 
> I only found this out because I read the C18 user manual.
> Something it has that I haven't seen before is a “long short” - a 24bit signed integer type! (also an unsigned long short too)
> 
> I’ve made a spreadsheet which was the basis for the math.
> I will try with Mac gcc. Part of the fun is gcc (64bit) will have a vastly different idea of what an int is compared to C18 (8bit)!
> I’ll have to change data types between the two compilers.
> The “uint8_t” style declarations don’t seem to work - I haven’t found a C18 stdint.h header. I prefer these to remove this sort of ambiguity!
> 
> I’ll let you know how that step goes.
> 
> Edward
> 
>> On 2/02/2017, at 7:23 PM, Mark Webb-Johnson <mark at webb-johnson.net <mailto:mark at webb-johnson.net>> wrote:
>> 
>> Edwards.
>> 
>> First I’ve heard of this, but it doesn’t surprise me.
>> 
>> Testing this sort of stuff is not particularly easy. What we have done in the past is put in a DIAG mode command to allow this function to be called with a given string parameter, and then to print the result. Then, we can script up something to feed in a bunch of input and see what the output is like. But, that does require physical hardware.
>> 
>> Perhaps also the function could just be run in a standalone C program on the mac? So long as the type sizes are the same, the results should be equivalent (perhaps with some float rounding differences in the original version).
>> 
>> Regards, Mark.
>> 
>>> On 2 Feb 2017, at 4:38 AM, Edward Cheeseman <cheesemanedward at gmail.com <mailto:cheesemanedward at gmail.com>> wrote:
>>> 
>>> 
>>>> On 23/01/2017, at 8:12 PM, Edward Cheeseman wrote:
>>>> 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.
>>> 
>>> I totally overestimated the pic18F capability.
>>> So it turns out the C18, and for that matter, the XC8 compilers treat long long the same as long - 32bit.
> 

Edward Cheeseman
Electrical Engineer
cheesemanedward at gmail.com

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