Hi Thomas & Frank: Laying out a coordinate grid system to mark wall sundial faces can get very tedious especially if there are lots of curved analemmas. Have you considered using the eassy method that most of the wall sundial painters in Italy, France and Austria use? I call it the "connect the dots" method. See this webpage that discusses this easy technique: http://advanceassociates.com/WallDial/TechnicalInfoPage.html
Design Transfer to Wall: The typical way of transferring a drawing to a wall is the "connect the dots" method: 1.First, make a full size drawing of the sundial on paper or Mylar plastic. I greatly prefer to use Mylar because it is much more durable and water-proof than paper and it won't tear, shrink or expand and can be reused many times. 2.Put the drawing on a table with foam board underneath it. Then using a sharp leather awl (like a short ice pick), punch holes into the lines on the drawing. Curved lines require more closely spaced holes than straight lines 3.Tape the drawing to the wall using painters tape making sure that it is level and correctly positioned on the wall. Using Sharpee waterproof marker pens, make dots on the wall through the holes in the drawing. 4.Remove the drawing from the wall and connect the dots on the wall using Sharpee waterproof pens. Use a straight edge ruler to connect the dots of straight lines and use freehand or a French curve to connect the dots of curved lines. 5.Begin painting in layers. When I made my wall dial, I painted the colors between the lines first, and then I painted the lines, numerals and artwork on top in layers. Each time I painted a different layer, I had to retape the drawing to the wall and mark the dots during the painting process. Usually, it takes a couple of coats of paint to get good coverage. 6.When finished painting, attach the gnomon to the wall. John Carmichael -----Original Message----- From: sundial-boun...@uni-koeln.de [mailto:sundial-boun...@uni-koeln.de] On Behalf Of Frank King Sent: Wednesday, December 09, 2009 12:55 AM To: Thomas Steiner Cc: sundial@uni-koeln.de Subject: Re: Das Ergebnis Ihres e-Mail-Kommandos Dear Thomas, I am becoming addicted to your project! I would love to come and be your assistant but I would need too many layers of thermal clothing at this time of year!! > And I could improve the script to handle > non-flat (not plane) walls, if you give > me a (simple) mathematical description > of it. OK, here is a mathematical description that is quite simple: All wall ARE flat, but only locally! You can divide your wall up into squares. It depends how unflat it is but sometimes squares of 500mm x 500mm will be OK. If the wall is very irregular, you may need squares of 100mm x 100mm. You have to obtain a LOT of survey measurements but, for each square, you estimate the local nodus height. You then use that nodus height for the little bit of sundial that goes across that square. Some squares will be blank so no problem. > ... the scaffolding will be removed after > xmas, so I have to hurry... I understand the problem. Scaffolding is expensive. I have TWO questions: Have you fixed the nodus yet? Do you get any sunny days at the moment? If both answers are yes, then you can mark a set of points where the shadow of the nodus falls on the wall at various times of day. Do this tomorrow!! It is important to put a sequence number against each point and the exact time of the observation. You then note the positions of each point on the wall. So, for each point, you have a sequence number, a time and a position. Then, back in the warm by your computer, you compare the actual positions with the predicted positions. You will see some irregularities which are just observational errors but if you see that all the points are a bit too low that that means the wall is leaning towards you a little. If just a few points are too low that means a local dip in the wall. If they are too high, that means a bump and so on. You can then go out into the cold and do some more surveying!! I envy you the project; I don't envy you doing it at this time of year!! Best wishes Frank --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
