Am 29.07.2002 17:01:26 schrieb "fer j. de vries" <[EMAIL PROTECTED]>:
>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. >> >> - >> > > > >- > -
