All,
I'm sorry I was only half awake when this thread started so forgive me if
I'm off course. If I had to lay out a large dial (say 100 ft) to a high
degree of accuracy (say .1 of an inch) I would plot all the points not as
x,y co-ordinates. I would plot them all out as the intersection of two
lines from two fixed points.
To see what I mean pick 2 points that are well established, e.g., point A
where the gnomom meets the dial face, and point B some number of feet due
north (in line with the gnomon base) of point A. Every point on the dial
face is now at the intersection of two tape measures that start at points A
and B. Assuming that the dial face is flat the accuracy would be good as
the tape measures used. For the points that are almost inline with the AB
line, a third point C could be used as one of the points. Point C could be
calculated from points A and B. Of course the computer would have to
calculate all of the points for you.
As a crude ASCII art: Point X is 30" 1 1/4" from point A, and 22" 3 7/8"
from point B. (A metric tape measure would be a lot handier)
B
\
\
\
\
\
/ X
/ C
/
/
/
/
/
/
A
-----Original Message-----
From: John Carmichael <[EMAIL PROTECTED]>
To: François BLATEYRON <[EMAIL PROTECTED]>
Cc: sundial@rrz.uni-koeln.de <sundial@rrz.uni-koeln.de>
Date: Tuesday, May 25, 1999 9:45 AM
Subject: frame & grid method
>
>
>>Perhaps a precise solution would be to calculate the intersection of the
>>hour line with the enclosing frame of your sundial. It must be done by a
>>computer but its easy to give a very good precision.
>>
>>The result would be given as a length and a direction (north, east, south,
>>west side of the sundial), the origin could be one of the two opposite
>>corners.
>>
>>The only problem then is to precisely draw your frame, with parallel sides
>>and a good perpendicularity.
>>
>>With one intersection point you can draw the line by joining it to the
>>gnomon foot.
>>
>>I plan to include such kind of data in my Shadows program in a futur
>>version.
>
>Bonjour Francois and everyone else:
>
>Your frame method for plotting would be a good practical way to implement
>John Pickard's (x,y) coordinate method. With a squared frame around the
>sundial work area, one could use it as a reference to easily measure the
>horizontal and vertical distances to the x,y coordinates.
>
>Let us know when you get your new shadows program up and running. Do you
>think I'd understand it or would I have to get someone to help me?
>
>merci Francois,
>
>John Carmichael
>
>
