Hey Wouter, My thought exactly. The point however is to know what time (universal time) corresponds with what longitude/center of the circle. Without taking dates into account; just a number of elapsed days since a reference date it's sure the center was at 0° lat/0° lon. From there on, everything is relative to that date.
Are there any sources mentioning these kind of reference dates ? I thought of applying a cycle of 365,25 days / year. But I guess this might build up an error after a while. Any clues on this ? Thanks ! Jan >----- Oorspronkelijk bericht ----- >Van: Wouter Schaubroeck [mailto:[EMAIL PROTECTED] >Verzonden: dinsdag, april 22, 2008 10:05 PM >Aan: [EMAIL PROTECTED] >CC: [email protected] >Onderwerp: Re: [Geotools-gt2-users] Drawing the night > >Actually, i think that is rather easy to do. You just take a circle, >and reproject it into your coordinate system. The radius of the circle >is the earth radius, and the middlepoint is the position on the earth >where the sun is in the zenith for that moment. > >The only thing you need is the position of the sun. Even this one is >rather easy to calculate: >Around 21st of march and december is the sun in the zenith on the >equator. The 21st of june is the sun in the zenith on the tropic of >cancer (23°44' N) (kreeftskeerkring ;) ) and the 21st of december the >sun is in the zenith on the tropic of capricorn (23°44' S) >(steenbokskeerkring). The last thing there is to know is that the sun >always moves between these two tropics and therefor describing a >sinus. Now it's possible to create a function that describes this >movement, and voila, you have your coordinates of the center of the >circle! > >If you have any more questions, feel free to ask > >grtz, > >Wouter Schaubroeck > >On Tue, Apr 22, 2008 at 4:43 PM, [EMAIL PROTECTED] ><[EMAIL PROTECTED]> wrote: >> Anybody ever had an attempt in drawing the night area of the planet ? >> >> I'm trying to figure out a simple way, based on a timestamp, to darken the >> area of the map representing the night. Preferably using vector data so I >> can check whether it's day/night on a certain point on the planet. >> >> Many thanks for any clue ! >> >> Jan >> >> >> >> ------------------------------------------------------------------------- >> This SF.net email is sponsored by the 2008 JavaOne(SM) Conference >> Don't miss this year's exciting event. There's still time to save $100. >> Use priority code J8TL2D2. >> >> http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone >> _______________________________________________ >> Geotools-gt2-users mailing list >> [email protected] >> https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users >> > ------------------------------------------------------------------------- This SF.net email is sponsored by the 2008 JavaOne(SM) Conference Don't miss this year's exciting event. There's still time to save $100. Use priority code J8TL2D2. http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone _______________________________________________ Geotools-gt2-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users
