# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Circle charts
From: Richard M Pisko
Date: 2009 Jan 27, 19:07 -0700

```On Thu, 15 Jan 2009 01:04:44 -0700, Nicol�s de Hilster
wrote:

> These circle charts were made on the job by the surveyor and showed only
> what the navigator needed, in most cases that were a few known points, a
> bit of coast line, an outline of the working area and of course the
> circles. The charts were used for small area's of only a few kilometres
> in diameter and usually made of paper (A1 or A0 size).

As a practical method, did you calculate the centers of the circles (on
the perpendicular bisectors of each line joining pairs of shore stations)
for drawing the chart of current interest?  Or did you use an adjustable
triangle, set to the double angle of the "observation angle", and find the
center for the circle of that observation angle graphically?   Or
(made of two pivoting straight edges) and use a (mechanical) pencil in the
vertex to trace out a circle.  Also, what would be the average degree
spacing of the chart's circles?

It seems as though there is a fair amount of work to set up a chart like
that without modern aids such as a computer, and you would have to make a
large number of observations to make it worth while.  I wish I were
skilled enough to use something like Gnuplot for doing a circle chart of
our river-bottom flats, using some reference points 200 to 300 feet above
the somewhat uneven work area.

Easier to locate your position using a plane table or theodolite than with
a sextant; and many software packages for total stations include the three
point problem solutions.

--
Richard . . .

Using Opera 9.2.4 after the "Dog" died

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