arimo at iki.fi
Mon Jun 16 20:33:12 BST 2008
After trial-and-error a found ure avlue of 40 meters high enough for
Globalsat sirf-3-based receiver, not tested with others yet.
Of course with values like this the estimated gps error makes no sense
and also the tripmeter lacks behind somewhat for shorter trips, for
longer trips the errors does not matter.
Only relation between DOP and actual error is that with hign DOP values
the variation in reported location migth be greater. Another way to
determine the accuracy would just be to divide some user-defined value,
for example 200, with the number of actively used satellites. Even better
would be satellites minus three and tripmeter is not update if the number
of satellites is below four.
I'll continue the search to find also the minimum usable value for some
receivers before the error increases too much.
Btw: counting distance in one meter resolution will give wrong sense of
accuracy. It would be better to use rounded-up values to next full ten
meters or 50 ft.
You can still escape from the Gates of hell: Use Linux!
mr. M01510 & guide Loadstone-GPS
On Sun, 1 Jun 2008, Shawn Kirkpatrick wrote:
> Once you find the propper ure for your receiver things should be fine since
> the accuracy value goes up with a bad signal.
> A manual update for a trip meter makes no sence since it wouldn't take in to
> account things like turns that may double back on the route. It would be
> like riding in a car and having to hit a button to make the odometer count
> up, that just doesn't happen. The trip meter may be slightly inaccurate but
> it'll really depend on your receiver, if you have bad drift you'll have more
> trouble than the trip meter.
> On Mon, 2 Jun 2008, Ari Moisio wrote:
>> Current value works best with static navigation -spoiled devices. It
>> is however usually not the failure of receiver but the temporary failure
>> in the receiving condition that makes the excessive drift.
>> Could you please elaborate, what makes the manual alternative in the
>> ripmeter 'ridiculous'? If we have for example a city with street corners
>> with better reception condition as the streets between them. Would it make
>> sense to update the tripmeter fewer times with a good signal condition
>> than many more times with more erroneus signal?
>> You can still escape from the Gates of hell: Use Linux!
>> mr. M01510
>> On Sun, 1 Jun 2008, Shawn Kirkpatrick wrote:
>>> The default ure value should work for most good receivers. Getting a propper
>>> value for your particular receiver may be trial and error. If you have that
>>> much drift then you'll probably have speed trouble as well.
>>> The trip meter in exploration mode is on the todo list.
>>> Manually updating the trip meter is a bit ridiculous, you don't do that
>>> anywhere else.
>>> On Sat, 31 May 2008, arimo at iki.fi wrote:
>>>> Tripmeter is a nice feature but...
>>>> - Using user range error to calculate minimum movement to count is too
>>>> low. I have set URE to 10 meters, quite high value for decent receivers
>>>> but still walked almost 400 meters just sitting on my garden. Finding a
>>>> good value for minimum movement is trial and error but current value is
>>>> too low. I'll look for higher values for URE if they would help.
>>>> - Also not updatin the tripmeter if speed is below static threshold d
>>>> might help.
>>>> - There could a manual mode where distance is advanced only by user
>>>> request or by giving any LS command.
>>>> - There could be a parallel tripmeter counting from zero everytime LS
>>>> is started.
>>>> - There could be a tripmeter-like functionality in the exploration mode
>>>> - LS converts stored distance kilometers to meters when closed and
>>>> launched again.
>>>> You can still escape from the Gates of hell: Use Linux!
>>>> mr. M01510
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