>Could you also elaborate on why a noncartesian system was used to mark the
>placement of the anchor points?
>
>-Bill Gottesman
This radial vs Cartesian discussion has come up before for large analemmatic
dials. Cartesian coordinates are not easy to lay out in the field. The X and
Y distances are easy but they must be at right angles to the axes. Radial
(r, theta) measurements have a similar problem . The distance is easy but
the accurate measurement of the angle is not unless you have a transit or
similar surveying device. In the analemmatic design spreadsheet Helmut and I
originally provided both Cartesian and radial coordinates. Then someone on
this list suggested a two arc technique as would be used by the ancient
Greeks. For one arc, measure the distance from the center and for the other
measure from the y axis semi diameter (b) point where the ellipse crosses
the y axis. The intersection of the two arcs determines the hour point. This
requires two tape measures and more helpers but these are usually easy to
get. This is much easier than measuring distances and angles.
I am sorry that I forget who made this good suggestion but you have my
thanks. We have incorporated the calculation of this y axis distance into
the design spreadsheet "Analemma.xls" still available on Helmut
Sonderegger's website. http://web.utanet.at/sondereh/sun.htm
Roger Bailey
Walking Shadow Designs
N 48.6 W 123.4
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