Agreed.
BJB

--- In BoundaryPoint@y..., David Mark <dmark@g...> wrote:
> You may be right, vertical may be defined by an ellipsoid
approximating
> the geoid. I am sticking to my point that the degree of latitude
varies
> systematically, and is LARGER near the poles (latitude as solid
> earth-center angle plus a polar-flattened earth would yield SHORTER
> degrees near the pole. And if mid-way between pole and equator is
defined
> by distance, 45 latitude is not exactly the answer.
>
> David
>
> On Sat, 7 Jul 2001 bjbutler@b... wrote:
>
> > David, how do you define "vertical"? Surely not gravitationally
> > because variations in rock density, elevation, and even
geometrical
> > latitude would produce "lines" of latitude that were iso-vertical
> > contours. I thought geocoordinates were expressed as angles
within
> > an ellipsoid (i.e. a datum), a better approximation of the
earth's
> > shape but still a mathematically regular object. I don't know if
> > these data contain local corrections.
> >
> > BJB
> >
> > --- In BoundaryPoint@y..., David Mark <dmark@g...> wrote:
> > > Technically, of course, the 45th parallel is not precisely half
way
> > > between the equator and the pole. It would be if the earth
were a
> > sphere.
> > > But since the earth is somewhat flattened pole-to-pole compared
> > with the
> > > equator, the length of the degree of latitude is not constant
but
> > itself
> > > varies with latitude.
> > >
> > > Many people mistake the definition of latitude. It is not a
solid
> > angle at
> > > the center of the Earth between a line to the center and the
plane
> > of the
> > > equator. Latitude of a point on the Earth's surface is the
angle
> > between
> > > the vertical and the plane of the equator. These two
definitions
> > also
> > > would be identical on a sphere.
> > >
> > > Due to the true definition of latitude and the flatteneing, the
> > length of
> > > a degree is a little larger toward the poles and smaller near
the
> > equator.
> > > So the 45th parallel is closer to the equator than to the pole,
and
> > the
> > > midpoint between the pole and the equator would be somewhat
north
> > of the
> > > 45th, how far I'm not sure (I have books at the office in which
I
> > could
> > > look this up).
> > >
> > > David
> > > dmark@g...
> > >
> > > On Fri, 22 Jun 2001, Bill Hanrahan wrote:
> > >
> > > > And if it wasn't halfway to the North Pole, it wouldn't be
the
> > 45th
> > > > parallel (Northern Hemisphere of course) in the first place.
> > > >
> > > > Bill
> > > >
> > > > At 05:51 PM 6/22/01, you wrote:
> > > > >It is also marked in Maine. I think I have seen it on Route
1.
> > > > >There is a monument and a plaque that says something about
> > > > >being "halfway to the north pole". But then, everywhere is
> > halfway
> > > > >to the north pole from somewhere!
> > > > >
> > > > >BJB
> > > >
> > > >
> >
> >
> >
> >
> > Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
> >
> >
> >