Re: [Gpsbabel-code] patch to increase precision in unicsv.c

[Robert L. <rob...@gp...>]

OK.  I'll roll on this one.  I applied it and cleaned the wreckage in the
test suite's reference files.   Please do a 'testo' on the next patch
submission as that makes it easier for me to rubber stamp things.

Thanx,
RJL

On Wed, Dec 2, 2009 at 5:14 PM, Hamish <ham...@ya...> wrote:

> Robert wrote:
> > Under what circumstances does this patch actually improve
> > precision?
>
> after a trip into the field last week I was downloading &
> converting the data and losing info in the process. Specifically
> river depths from the sounder are better than 10cm while
> shallow, and temperature is given better than 0.1 deg C.
> This was from a consumer grade Garmin depth sounder.
>
> HDOP et al were just along for the ride, the idea being that
> units using meters should report to the mm (to accomodate
> survey grade/RTK GPSs). For lat/lon that means about %.9f btw.
>
>
> >  Do you really have a device that returns temperature to a
> > thousandth of a degree
>
> actually I do, but that's a bit besides the point & I'm not
> really asking you to support research gear (but for the cost
> of 1 sigf dig that would sure be nice).
>
> good thermistors are pretty cheap these days, something that
> gets you to better than 0.1 deg C is less than $0.50 so lots
> of things have that. The idea of going to 0.001 deg instead
> of 0.01 deg was to avoid introducing any FP rounding errors.
> (mostly an issue for lat/lon which needs to be stored in a
> double, but after tearing my hair out so many times due to
> that (after the source data was gone) I try to preserve
> precision+1 for everything now and let gzip worry about any
> added zeros)
>
>
> > or that returns DOP with meaningful values in the hundredths
> > position?
>
> DOP was just to standardize at 1mm reporting. No arguement that
> that will be slight overkill. I'll have a peek at some of our
> Trible logs and see if I get any really tiny DOP numbers out of
> that (should be good to about 2mm position in the horizontal).
> I've got a feeling that the DOP there is in pseudo-meters though,
> Gpsd has some code to convert, I'm not really sure how correct
> their approach is though.
>
> > If there is actually valid information, I
> > don't mind bloating the output,
>
> sure, I see your point.
>
> for bit balance, the GPX output doesn't need to go to %.6f for
> those things.
>
> > but it's not like speed (which is almost always computed and
> > not measured)
>
> are you sure about that? I seem to recall something recently
> discussing how the speed solution was often better than fix as
> it took phase differences into account.
>
> > from consumer grade GPS has two significant digits past the
> > decimal.
>
>
>
> thanks,
> Hamish
>
>
>
>
>