Well, here am I again, after three successive virus attacks, a
hardware failure ("carpets and CD units are incompatible" told me the
guy at the shop!)
and a lot of work kept me isolated from the outer world. I'm trying to
recover my e-mail folders from a post-mortem backup, so I do not know what
has been going on in the list, but as far as I remember, some of you
asked me for the formulae for an analemmatic sundial having its
(moveable) gnomon
inclined. There they go (copied from Savoie 's book):
Let's consider a set of ortogonal axis centered in the foot of the
gnomon and pointing towards the East (x), North (y) and Zenith (z). Let
be as well
i the angle from the vertical line to the gnomon (i = 0 means a vertical
gnomon, and i=90 an horizontal one), and D its gnomonical declination
(D=0 means
a gnomon pointing to the South, D=90 is pointing to the West and so on).
The coordinates of the ellipse of hours are:
x = -r*(tan(i)*sin(D)*cos(Lat)*cos(HourAng) - sin(HourAng))
y = -r*cos(HourAng)*(tan(i)*cos(D)*cos(Lat)-sin(Lat))
where r is a free parameter (it stands for the radius of the equatorial
circle from which the dial derives).
And the scale of dates is still a straight segment whose coordinates are:
X = r*tan(i)*sin(D)*sin(Lat)*tan(SunDecl)
Y = r*tan(SunDecl)*(tan(i)*cos(D)*sin(Lat)+cos(Lat))
From them you can derive all the projection sundials like
Foster-Lambert's, Parent,'s, and a lot of curious new ones.
Sorry about the delay!
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