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Fred,
Thanks a lot.
How did you find my appartment,
by the address or by co-ordinates?
:-)

Alex.

On Tue, 31 Oct 2006, Fred Hebard wrote:

>
>
> Alex,
>
> It's full featured.  There's a search box, and you can change the
> size and zoom of the map, and look at maps of different scale.  It
> starts out with the 7.5' series maps.  The captions are cut off, but
> the contours have elevation in feet above sea level marked here and
> there, always on the darker lines, and you can count the divisions
> between.  Your apartment in West Lafayette has the 670 contour
> running through the middle.  The fine contours there are at 10 foot
> intervals.
>
> Fred
>
> On Oct 31, 2006, at 12:51 PM, Alexandre E Eremenko wrote:
>
> >
> >
> > 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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