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Thanks, Fred.
This seems to be a demo with limited features,
and I am not sure where on the map elevation
is shown, and in which units.
Can you give an example?

Alex

On Tue, 31 Oct 2006, Fred Hebard wrote:

>
>
> Alex,
>
> The website, http://www.topozone.com/ has topographic maps covering
> the U.S., from which you can extract your elevation to the nearest 20
> feet or so, which is close enough.
>
> Fred
>
> On Oct 31, 2006, at 10:33 AM, Alexandre E Eremenko wrote:
>
> >
> >
> > Jean-Philippe,
> > Thanks.
> > I have no problems with conversion of units,
> > (though it is sometimes annoying with pressure
> > for which at least 5 different units are commonly used:
> > psi(=punds/square inch), millibar(=1000 dynes/square centimeter),
> > Pascal (not to be confused with psi:-),
> > inches of mercury and
> > millimeters of mercury.
> > And I almost forgot the sixth unit: the atmosphere:-)
> >
> > Most barometers on e-bay use one or two of these units,
> > so one has to hand a conversion table besides the barometer:-)
> >
> > Is there a convenient source on the web to find one's altitude
> > over the sea level, (I mean for those unfortunate ones
> > who do not live on a sea shore)?
> >
> > Alex.
> >
> > On Tue, 31 Oct 2006, jean-philippe planas wrote:
> >
> >> If you know the elevation of your observation spot as well as the
> >> atmospheric pressure reduced to sea level (QNH for the pilots) you
> >> can determine the local pressure (QFE for the pilots) knowing the
> >> fact that every 28 ft of altitude the pressure decreases by 1
> >> millibar in the lower standard atmosphere . I'll look for the
> >> formula in inches of mercury if its the way the weather channel
> >> provides this info.
> >>   JPP
> >>
> >> Fred Hebard  wrote:
> >>
> >> That's correct! I started looking into this, but gave up.
> >> Hopefully, the physicists will jump in here.
> >>
> >> On Oct 31, 2006, at 8:59 AM, Alexandre E Eremenko wrote:
> >>
> >>>
> >>>
> >>> Fred,
> >>> I see, this sounds reasonable.
> >>> But then I need a barometer, or to correct
> >>> the pressure from the Weather channel for
> >>> my altitude, because,
> >>> if I understand correctly, the pressure broadcast
> >>> for the weather prediction is reduced to the sea level.
> >>>
> >>> Alex
> >>>
> >>> On Tue, 31 Oct 2006, Fred Hebard wrote:
> >>>
> >>>>
> >>>>
> >>>> Alex,
> >>>>
> >>>> Use the actual pressure. That is the determinant for the refraction
> >>>> correction. The elevation above sea level has an insignificant
> >>>> effect on parallax, when you consider that the radius of the
> >>>> earth is
> >>>> about 3400 nautical miles, but significantly reduces refraction via
> >>>> the effect on barometric pressure.
> >>>>
> >>>> Fred
> >>>>
> >>>> On Oct 31, 2006, at 8:27 AM, Alexandre E Eremenko wrote:
> >>>>
> >>>>> Related question: the barometric pressure in the refraction
> >>>>> formula.
> >>>>> Should I use the actual pressure at my observation site,
> >>>>> or should I "reduce it to the sea level"?
> >>>>> The actual pressure at my site reflects not only the deviation
> >>>>> from the standard atmosphere but also my altitude over the sea
> >>>>> level.
> >>>>>
> >>>>> Alex
> >>>>>
> >>>>
> >>>>
> >>>>>
> >>>
> >>>
> >>>>
> >>
> >>
> >>
> >>
> >>
> >>
> >> JPP
> >>
> >> ---------------------------------
> >> Get your email and see which of your friends are online - Right on
> >> the  new Yahoo.com
> >>
> >>>
> >
> >
> > >
>
>
> >


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