[Ovmsdev] Miles/Kilometers Conversion
Michael Balzer
dexter at expeedo.de
Wed May 15 20:20:17 HKT 2013
Mark, Tom,
cool stuff, I don't think this conversion can be done with any more
accuracy than that :-)
In the area of 0..100 km it tends to give smaller roundtrip results than
the old one, but I consider this to be OK, as this typically is the
"range" area and it should be better to be -2 km off for some values
than to be +1 km for more values.
Updated & checked in.
Regards,
Michael
Am 13.05.2013 15:11, schrieb Mark Webb-Johnson:
>
> I've committed Tom's functions for this, as well as changes to net_msg
> and vehicle_voltampera to use the new functions.
>
> Michael: I haven't changed vehicle_twizy, as I didn't want to mess
> with your module. The change is very simple:
>
> 1. s/KM2MI/MiFromKm/
> 2. s/MI2KM/KmFromMi/
>
>
> Once done, please remove the KM2MI and MI2KM macros from utils.h, as
> they shouldn't be required any more.
>
> The STAT command is a good way of testing. I tried in DIAG mode, and
> it seemed ok.
>
> Regards, Mark.
>
> P.S. Now the Android App is back in the store, I'll start the process
> of working out a better solution for this.
>
> On 13 May, 2013, at 9:02 AM, Mark Webb-Johnson <mark at webb-johnson.net
> <mailto:mark at webb-johnson.net>> wrote:
>
>> Michael,
>>
>> Sorry, I've been lax about this.
>>
>> I did some work with Tom, a while ago, but haven't had a chance to
>> put it in.
>>
>> Here is the final result (of me improving, then Tom improving my
>> improvements, then me improving Tom's improvements to my
>> improvements, then Tom nailing it with a last set of improvements).
>> In the end, we decided it was more important to be as accurate as we
>> can than to try to match the car exactly. As he put it, it was an
>> interesting problem, and I think the solution of dividing the problem
>> into two is quite elegant - leading to extraordinary accuracy on an
>> 8bit processor while still supporting a large range of values. I'm
>> particularly happy about the round-trip (miles->kilometers->miles)
>> values shown.
>>
>> Below is an improved version of the miles-to-kilometers function with
>> rounding to get a bit more precision, and a corresponding
>> kilometers-to-miles function.
>>
>> I tested both the functions with a bunch of values, converting
>> miles to
>> kilometers and back, using 32-bit ints representing 1/10's. It
>> matches the
>> odometer values you gave for your car and successfully roundtrips
>> until
>> 300,000 miles.
>>
>> Xcode Test results:
>>
>> 0.1 miles -> 0.2 km -> 0.1 miles
>> 1.0 miles -> 1.6 km -> 1.0 miles
>> 10.0 miles -> 16.1 km -> 10.0 miles
>> 100.0 miles -> 160.9 km -> 100.0 miles
>> 100,000.0 miles -> 160,934.4 km -> 100,000.0 miles
>> 150,000.0 miles -> 241,401.7 km -> 150,000.0 miles
>> 200,000.0 miles -> 321,868.9 km -> 200,000.0 miles
>> 299,999.9 miles -> 482,803.2 km -> 299,999.9 miles
>> 300,000.0 miles -> 482,803.3 km -> 299,999.9 miles
>> 1,000,000.0 miles -> 1,609,344.5 km -> 999,999.9 miles
>> 10,000,000.0 miles -> 16,093,444.8 km -> 9,999,999.1 miles
>> 200,000,000.0 miles -> 321,868,896.5 km -> 199,999,982.4 miles
>> 32,255.6 miles -> 51,910.4 km -> 32,255.6 miles
>> 32,285.8 miles -> 51,959.0 km -> 32,285.8 miles
>> 13,421.3 miles -> 21,599.5 km -> 13,421.3 miles
>>
>> Code:
>>
>> // convert miles to kilometers by multiplying by ~1.609344
>>
>> unsigned long KmFromMi(unsigned long miles)
>> {
>> unsigned long high = miles >> 16;
>> unsigned long low = miles & 0xFFFF;
>>
>> // approximate 0.609344 with 39934/2^16
>> // do the multiply and divide for the high and low 16 bits to
>> // preserve precision and avoid overflow
>> // this yields six significant digits of accuracy and doesn't
>> // overflow until the results no longer fit in 32 bits
>> return miles + (high * 39934) + ((low * 39934 + 0x7FFF) >> 16);
>> }
>>
>> // convert kilometers to miles by multiplying by ~1/1.609344
>>
>> unsigned long MiFromKm(unsigned long km)
>> {
>> unsigned long high = km >> 16;
>> unsigned long low = km & 0xFFFF;
>>
>> // approximate 1/1.609344 with (40722 + 1/6)/2^16
>> // do the multiply and divide for the high and low 16 bits to
>> // preserve precision and avoid overflow
>> // this yields six significant digits of accuracy and doesn't
>> // overflow for any 32-bit input value.
>> return (high * 40722) + ((low * 40722 + km/6 + 0x7FFF) >> 16);
>> }
>>
>> I hope this is useful. It was an interesting problem.
>>
>> Tom
>>
>>
>> I'll put it in utils.c this evening.
>>
>> It is not a _perfect_ solution (which would be to get the readings in
>> native format - but that needs synchronised changes to the protocol
>> and apps to support both new and old formats), but should be a lot
>> more accurate than what we have now.
>>
>> Regards, Mark.
>>
>> On 13 May, 2013, at 4:48 AM, Michael Balzer wrote:
>>
>>> Nikki,
>>>
>>> that's no new error, it's due to the Twizy measuring metric vs. the
>>> OVMS car model needing miles.
>>>
>>> The kilometer to miles conversion is optimized to avoid floating
>>> point math (the OVMS has no FPU), and the conversion is already fine
>>> tuned to produce the least mean error in the range 0..100 km.
>>>
>>> Conversion errors get bigger the bigger the numbers get, and there's
>>> not much we can do about this (except enabling metric values in the
>>> car model, which is on our list).
>>>
>>> Here's your current error explained:
>>>
>>> MP-0 c200,0,0040,0000,0000,4,0,0,169252,8430,8430,8774,65,65,41,37,0
>>>
>>> 169252 is the Twizy internal odometer value meaning 1692.52 km.
>>>
>>> See utils.h for the conversion:
>>>
>>> // 1 mile = 1.609344 kilometers
>>> // smalles error approximation: mi = (km * 10 - 5) / 16 + 1
>>>
>>> So the integer conversion for 1692 results in 1058 while the real
>>> value is 1051. That's your 7 mile offset.
>>>
>>> Regards,
>>> Michael
>>>
>>>
>>> Am 12.05.2013 21:49, schrieb Nikki Gordon-Bloomfield:
>>>> I forgot to mention...
>>>>
>>>> My Twizy is about 7 miles less on the odometer than the creek OVMS
>>>> build says.
>>>>
>>>> Sent from my iPhone
>>>>
>>>> On 12 May 2013, at 17:40, Michael Balzer <dexter at expeedo.de
>>>> <mailto:dexter at expeedo.de>> wrote:
>>>>
>>>>> Nikki,
>>>>>
>>>>> I haven't had that special case, but it sounds like the RAM
>>>>> corruption effect. I think you need to do a hard reboot, i.e.
>>>>> switch the module off.
>>>>>
>>>>> Please read out the debug info (cmd 200) and send me all history
>>>>> data if possible, maybe I can find something in there.
>>>>>
>>>>> Thanks,
>>>>> Michael
>>>>>
>>>>>
>>>>> Am 12.05.2013 13:26, schrieb Nikki Gordon-Bloomfield:
>>>>>> HI folks,
>>>>>>
>>>>>> Just to let you know that my Twizy is still reporting 0 percent
>>>>>> and 0 miles, even though it is now fully charged! (At least, OVMS
>>>>>> is!) I've rebooted it a few times, and geolocation works fine.
>>>>>>
>>>>>> Nikki.
>>>>>>
>>>>>>
>>>>>>
>>>>>> On 12 May 2013, at 12:09, Michael Jochum <mikeljo at mac.com
>>>>>> <mailto:mikeljo at mac.com>> wrote:
>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>> i think yes.
>>>>>>> We have the Voltage(s) and Amper(s) per Motor and Battery. But
>>>>>>> currently not used in OVMS.
>>>>>>> So we can calc the Power like DashDaq.
>>>>>>>
>>>>>>> I think these are the IDs:
>>>>>>>
>>>>>>> 7EC 432D High Voltage Battery Voltage
>>>>>>> 7EC 4356 High Voltage Battery Current
>>>>>>>
>>>>>>> 7E9432D High Voltage Battery Voltage
>>>>>>> 7E94356 High Voltage Battery Current
>>>>>>>
>>>>>>> 7E92883 Motor A DC Current
>>>>>>> 7E92884 Motor B DC Current
>>>>>>> 7E92885 Motor A DC Voltage
>>>>>>> 7E92886 Motor B DC Voltage
>>>>>>>
>>>>>>> 7E8000D Vehicle Speed Km/Hr
>>>>>>>
>>>>>>> You can see the Data for the Battery are here twice. For Filter
>>>>>>> reasons i think it is better to use 7E9 instead 7EC.
>>>>>>>
>>>>>>>
>>>>>>> Bye
>>>>>>> Michael J.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Am 11.05.2013 um 21:05 schrieb Denis KRAUTH
>>>>>>> <denis.krauth at wanadoo.fr <mailto:denis.krauth at wanadoo.fr>>:
>>>>>>>
>>>>>>>> Michael (J),
>>>>>>>> Is this feasible for our Amperas ?
>>>>>>>> Denis (aka Kratus).
>>>>>>>> *De :*ovmsdev-bounces at lists.teslaclub.hk
>>>>>>>> <mailto:ovmsdev-bounces at lists.teslaclub.hk>[mailto:ovmsdev-bounces at lists.teslaclub.hk
>>>>>>>> <mailto:bounces at lists.teslaclub.hk>]*De la part de*Michael Balzer
>>>>>>>> *Envoyé :*samedi 11 mai 2013 16:52
>>>>>>>> *À :*ovmsdev at lists.teslaclub.hk <mailto:ovmsdev at lists.teslaclub.hk>
>>>>>>>> *Objet :*Re: [Ovmsdev] Twizy firmware image V2.3.6 / 2.6.5
>>>>>>>>
>>>>>>>> Denis,
>>>>>>>>
>>>>>>>> thanks :-)
>>>>>>>>
>>>>>>>> The GPS logging feature and energy usage stats are currently
>>>>>>>> Twizy specific.
>>>>>>>>
>>>>>>>> To move these into the framework, we need to make the energy
>>>>>>>> usage variables part of the common car model. And of course we
>>>>>>>> need to know how to get these values from other cars like
>>>>>>>> Ampera...?
>>>>>>>>
>>>>>>>> Regards,
>>>>>>>> Michael
>>>>>>>>
>>>>>>>> Am 11.05.2013 10:17, schrieb Denis KRAUTH:
>>>>>>>>
>>>>>>>> Wow, great !
>>>>>>>> Can this be done on my Ampera too, or is it Twizy-specific ?
>>>>>>>> Can FEATURE 8 2 also be applied on my 2.3.2 Ampera firmware?
>>>>>>>> There is a Volt/Ampera ecodrive contest in a few days (June
>>>>>>>> 1^st ) and this would be really great to track the data.
>>>>>>>> I just read your german guide, and it seems really not
>>>>>>>> difficult.
>>>>>>>> Hut ab!
>>>>>>>> Denis.
>>>>>>>> *De :*ovmsdev-bounces at lists.teslaclub.hk
>>>>>>>> <mailto:ovmsdev-bounces at lists.teslaclub.hk>[mailto:ovmsdev-bounces at lists.teslaclub.hk]*De
>>>>>>>> la part de*Michael Balzer
>>>>>>>> *Envoyé :*vendredi 10 mai 2013 20:26
>>>>>>>> *À :*'OVMS Developers'
>>>>>>>> *Objet :*[Ovmsdev] Twizy firmware image V2.3.6 / 2.6.5
>>>>>>>> For those avoiding self-compiling (Nikki et al), here's the
>>>>>>>> current firmware image with Twizy extensions.
>>>>>>>>
>>>>>>>> It makes GPS logging (RT-GPS-Log) at 5 second intervals stable.
>>>>>>>>
>>>>>>>> To get max GPS precision be sure to activate only the GPS
>>>>>>>> logging (w/o location streaming) by setting feature #8 to 2.
>>>>>>>>
>>>>>>>> The ZIP also contains a guide and spreadsheet template for
>>>>>>>> creating energy use heatmap-style GPS tracks using
>>>>>>>> gpsvisualizer.com <http://gpsvisualizer.com/> -- the guide
>>>>>>>> text is in german now, I can make an english version and
>>>>>>>> add it to the repository if there is demand.
>>>>>>>>
>>>>>>>> Here's an example result:
>>>>>>>>
>>>>>>>> <image001.png>
>>>>>>>>
>>>>>>>> Regards,
>>>>>>>> Michael
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> --
>>>>>>>>
>>>>>>>> Michael Balzer * Paradestr. 8 * D-42107 Wuppertal
>>>>>>>>
>>>>>>>> Fon 0202 / 272 2201 * Handy 0176 / 206 989 26
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> _______________________________________________
>>>>>>>>
>>>>>>>> OvmsDev mailing list
>>>>>>>>
>>>>>>>> OvmsDev at lists.teslaclub.hk <mailto:OvmsDev at lists.teslaclub.hk>
>>>>>>>>
>>>>>>>> http://lists.teslaclub.hk/mailman/listinfo/ovmsdev
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> --
>>>>>>>> Michael Balzer * Paradestr. 8 * D-42107 Wuppertal
>>>>>>>> Fon 0202 / 272 2201 * Handy 0176 / 206 989 26
>>>>>>>> _______________________________________________
>>>>>>>> OvmsDev mailing list
>>>>>>>> OvmsDev at lists.teslaclub.hk <mailto:OvmsDev at lists.teslaclub.hk>
>>>>>>>> http://lists.teslaclub.hk/mailman/listinfo/ovmsdev
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> OvmsDev mailing list
>>>>>>> OvmsDev at lists.teslaclub.hk <mailto:OvmsDev at lists.teslaclub.hk>
>>>>>>> http://lists.teslaclub.hk/mailman/listinfo/ovmsdev
>>>>>>
>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> OvmsDev mailing list
>>>>>> OvmsDev at lists.teslaclub.hk
>>>>>> http://lists.teslaclub.hk/mailman/listinfo/ovmsdev
>>>>>
>>>>> --
>>>>> Michael Balzer * Paradestr. 8 * D-42107 Wuppertal
>>>>> Fon 0202 / 272 2201 * Handy 0176 / 206 989 26
>>>>> <dexter.vcf>
>>>>> _______________________________________________
>>>>> OvmsDev mailing list
>>>>> OvmsDev at lists.teslaclub.hk <mailto:OvmsDev at lists.teslaclub.hk>
>>>>> http://lists.teslaclub.hk/mailman/listinfo/ovmsdev
>>>>
>>>>
>>>> _______________________________________________
>>>> OvmsDev mailing list
>>>> OvmsDev at lists.teslaclub.hk
>>>> http://lists.teslaclub.hk/mailman/listinfo/ovmsdev
>>>
>>> --
>>> Michael Balzer * Paradestr. 8 * D-42107 Wuppertal
>>> Fon 0202 / 272 2201 * Handy 0176 / 206 989 26
>>> <dexter.vcf>_______________________________________________
>>> OvmsDev mailing list
>>> OvmsDev at lists.teslaclub.hk <mailto:OvmsDev at lists.teslaclub.hk>
>>> http://lists.teslaclub.hk/mailman/listinfo/ovmsdev
>>
>
>
>
> _______________________________________________
> OvmsDev mailing list
> OvmsDev at lists.teslaclub.hk
> http://lists.teslaclub.hk/mailman/listinfo/ovmsdev
--
Michael Balzer * Paradestr. 8 * D-42107 Wuppertal
Fon 0202 / 272 2201 * Handy 0176 / 206 989 26
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.teslaclub.hk/pipermail/ovmsdev/attachments/20130515/ba98c1ea/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: dexter.vcf
Type: text/x-vcard
Size: 206 bytes
Desc: not available
URL: <http://lists.teslaclub.hk/pipermail/ovmsdev/attachments/20130515/ba98c1ea/attachment-0001.vcf>
More information about the OvmsDev
mailing list