Hello Mike, Nice idea to make a double glazing sundial. I dont know of any program to do the job for you but here you will find a solution to calculates such a dial. The window can have any declination or inclination as you want.
At my web site ( address below ) you may find a method to compute flat sundials. ( See the link at the site ) We need the main procedure of that method with some extra routines to solve the problem. For definitions and details look at my site. I suggest to place the shadow casting point at some distance from the outside pane to get a larger dial on your inside pane. That distance I call g1 If you don't want to do this just take g1 = 0 The thicknessof the outside pane is g2 The space between the two panes is g3 The thickness of the inside pane is g4 I assume: - the refraction index of glass is ref and equal for both panes. - the medium between the two panes acts like air with no extra refraction. - the panes are parallel. Of course you have to declaire values for latitude phi and for the dial's inclination and declination i and d. Because (nearly) all the lines on the sundial will become curved, you need to calculate a series of points ( decl, t ) for each line. decl is the sun's declination t is the hourangle of the wanted point. For each point decl, t do as is written below. In decl, t x0 = sin t . cos decl y0 = cos t . cos decl z0 = sin decl R = 90 - phi x1 = x0 y1 = y0 . cos R - z0 . sin R z1 = y0 . sin R + z0 . cos R if z1 < 0 point isn't real: sun is beneath the horizon. R = d x2 = x1 . cos R - y1 . sin R y2 = x1 . sin R + y1 . cos R z2 = z1 R = i x3 = x2 y3 = y2 . cos R - z2 . sin R z3 = y2 . sin R + z2 . cos R if z3 <= 0 point isn't real: sun isn't above the dial. These are the coordiantes of the sun relative to the window. Add new routine x4 = x3 / ref y4 = y3 / ref z4 = sqrt( 1 - x*x - y*y ) ( square root out of (...) ) These are the coordinates of the sun corrected with the refraction index ref. Now we have to calculate the shadowpoints on 4 sundials xa = x3 . g1 / z3 ya = y3 . g1 / z3 xb = x4 . g2 / z4 yb = y4 . g2 / z4 xc = x3 . g3 / z3 yc = y3 . g3 / z3 xd = x4 . g4 / z4 yd = y4 . g4 / z4 The final coordinates of the point are x = -( xa + xb + xc + xd ) y = ya + yb + yc + yd The x value gets a minus sign because you will draw the pattern from the opposite side as the gomon is. Use the two tests inside the procedure to exclude irrelevant points. Also exclude points that are very far away of your sundial. Show us what your final dial will be. Best wishes, Fer. Fer J. de Vries mailto:[EMAIL PROTECTED] http://www.iae.nl/users/ferdv/ Eindhoven, Netherlands lat. 51:30 N long. 5:30 E ----- Original Message ----- From: "The Shaws" <[EMAIL PROTECTED]> To: "Sundial list" <[email protected]> Sent: Sunday, July 28, 2002 8:53 PM Subject: Double glazing dial > I have wondered for a while if it was possible to make use of the two panes > of glass in double glazed units to make a window sundial. > > To try out the concept, I made a prototype dial using two panes of glass, > clamped 44mm apart (I just happened to have some wood that thickness). > The pane nearest to the sun carries a double arrow which acts as the gnomon > nodus. The inner glass carries the dial face. > > The dial was designed for a site which declines 76 degrees West of South - > the back of my house. > I used Francois Blateyron's Shadow programme - Version 6.2.1 > I have put a picture on my web page - follow the link to "Double Glazing > Dial" - there is a link to Jim Tallman's single glazing dial there as well. > > The frosting was applied from a spray can, and the clear areas were simply > masked off. For the lines, I used "Magic" tape - the type that doesn't show > up on photocopiers, cut into thin strips using a straight edge and craft > knife. The numbers were made by removing the frosting using a stencil and > Dremel drill fitted with a flexible drive shaft. > > In this dial, I frosted both the "inside" faces, so there is no glass > between the nodus and the dial face. Hence, no refraction problems. But in > the "real thing" I would have to use the "outside" surfaces, and account > would need to be taken of the refraction of two panes of glass. The effect > would change throughout each day, and through the seasons. The dial would > also be smaller, the gap between the panes in my units is only 20mm. > > A quick test (sticking OHP film on the windows) shows that errors of about > 15 minutes at the extremities - I guess the varying error is related to the > changing angle of incidence of the sunlight. > My mathematics isn't up to the three dimensions involved - can anyone help? > > Mike Shaw > > mailto:[EMAIL PROTECTED] > > http://homepage.ntlworld.com/jmikeshaw/ > > N 53º 21' 24" > W 03º 01' 47" > Wirral, UK. > > - > -
