Donald. Many ways to solve your problem and I add mine as I use in my program ZW2000 to calculate flat sundials . The procedures are published on the website of De Zonnewijzerkring. Address below. Look for: - Calculate and construct. - Flat sundials, extensive version.
Read the preface and definitions pages. And then in the main procedure you find what you asked in your mail. Needed input: Latitude Longitude Time as hourangle of the sun And the sun's declination. (And for sundials also d, i, g, declination and inclination of the dial's plane and the lenght of the (pin-)gnomom.) For your goal now calcuate: x0, y0, z0. The coordinates of the sun in the equatorial sytem of sun's declination and hourangle. x1, y1, z1. The coordinates of the sun in the horizontal sytem of altitude and azimuth >From the latter it is easy to calculate the wanted azimuth and altitude. This all in a sphere with radius of 1 unit. If you are also using the rest of the procedures, x3, y3, z3 give you the coordinates of the sun relative to the plane of the sundial. You still need procedures for a given day(-number) to calculate the declination of the sun and the equation of time. Again, many solutions can be found but in the page "endnotes" you may find my procudure. I calculate formulas for a given year. An example for 1998 is given. With equadecl you may calculate the formulas for any given year. I suggest to choose a year between two leapyears some years in future if you use this methode. Have fun with it. Fer. Fer J. de Vries De Zonnewijzerkring http://www.de-zonnewijzerkring.nl Molens http://www.collsemolen.dse.nl Eindhoven, Netherlands lat. 51:30 N long. 5:30 E ----- Original Message ----- From: Donald Christensen To: sundial@uni-koeln.de Sent: Wednesday, August 24, 2011 4:29 AM Subject: sun position I need to write a spreadsheet to find the sun position. I know there are already many programs that do this. However, I need to write one myself because: 1. I'll learn as I write 2. It will give the sun position in the format that I need 3. I can tweak the spreadsheet to give the same answer but in another format. My question is, where do I start? I want to input Latitude Longitude Time The sun position will then be in X Y Z coordinates. I'll back up. I'm drawing a sundial in Autodesk Inventor. I can place lights that represent the sun. I can move the lights while I film my animation and watch the shadows move. That's why I need the sun position in XYZ format. I want the shadows accurate. I don't need the sun to be 150,000,000 km away from my sundial. It only needs to be 100 meters away I want to first write it to output azmith and altitude. (or the same as other programs whatever the output is) I'll then tweak my spreadsheet to convert this to XYZ -- Cheers Donald 0423 102 090 This e-mail is privileged and confidential. If you are not the intended recipient please delete the message and notify the sender. Un-authorized use of this email is subject to penalty of law. So there! ------------------------------------------------------------------------------ --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
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