BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Earth sunrise math ?          BorlandTalk.com Forum Index -> C++ Builder (Graphics) View previous topic :: View next topic   Author Message Jim Davis Guest Posted: Tue Apr 10, 2007 8:10 am    Post subject: Earth sunrise math ? Need math for sunrise/sunset curve on earth map : Given a rectangular projected earth section map (Top&Bottom are Latitudes , Left&Right are Longitudes) . What is math for sunrise/sunset curve thru rectangular map ? Say for some map_Y , what is map_X of the "sunline" ? Cheers , Jim D Back to top Roger Guest Posted: Thu Apr 12, 2007 4:52 am    Post subject: Re: Earth sunrise math ? http://williams.best.vwh.net/sunrise_sunset_algorithm.htm may help, Roger Back to top Jim Davis Guest Posted: Thu Apr 12, 2007 8:10 am    Post subject: Re: Earth sunrise math ? Roger <aretae (AT) magma (DOT) ca> wrote in news:461d74b5 (AT) newsgroups (DOT) borland.com: Quote: http://williams.best.vwh.net/sunrise_sunset_algorithm.htm earth rotation 24 hours earth axis tilt 23.45 degrees orbit period 365.25 days elliptical orbit ignore maybe non spherical earth ignore for sure Given [TDateTime] , calc earth lat & long of sun zenith point , defining sunlite boundary - great circle . Given single earth [latitude] - small circle , maybe 2 intersections with above sunline great circle , calc 2 longitudes (sunrise & sunset) . Rectangular earth map file name includes map boundaries , first 3 digits integer degrees , like "San Bernadino.W120N034W11788N03288.BMP" . Have graphics map darkening code , approximatting curved twilight band with several trapizoids . Still need above spherical math . Back to top Jim Davis Guest Posted: Sat Apr 14, 2007 8:09 am    Post subject: Re: Earth sunrise math ? Quote: Rectangular earth map file name includes map boundaries , first 3 digits integer degrees , like "San Bernadino.W120N034W11788N03288.BMP" . struct { double Lat , double Lon } PointJ ; // earth point radians TabName : NamePoint NameType NameString NameTypeEnum { Country, State, City, Mountain, Water } ; TabPntLists : Pnts[] PntsLen PntsType PntsColor PntsTypeEnum {RoadRiver, Ocean, Continent country state desert forest lake} ; RoadRiver has PntsLen-1 lines Show RoadRiver if (HeightCalc(Pnts) < RoadRiverFraction * CanvasHeight) if(~RoadRiver) close area w/ line (Pnts[PntsLen-1], Pnts[0]) ?? area fill paints all points on area edge ?? TabAltitude : AltPoint Altitude ? sun longitude is linear function of TDateTime , independant of sun latitude ? lat 0 equator or northpole ? lon positive west of greenwich ? great circle on rectangle is somekinda ellipse ? pictures from space projection //----------------------------------------------------------------------------- //----------------------------------------------------------------------------- // http://geospatialmethods.org/spheres/GCIntersect.html // bottom of page : Great Circle intersects Latitude // ?? detect - return false if no intersection greatcircle with latitude //----------------------------------------------------------------------------- bool TwoLonEdge ( double& SunRisLon , // output sun rise longitude < pi west(+??) of sun double& SunSetLon , // output sun set longitude < pi east(-??) of sun PointJ Sun , // input sun lat & lon double MapLat ) // input latitude in map { double r,z,a,b,c,j,d,e,h,y0,y1,x0,x1 ; r = 1 ; // ?? z = r * sin(MapLat) ; a = 2 ; // ?? Sun.Lat Sun.Lon b = 3 ; c = 4 ; j = c * z ; d = (b*j) / (b*b + a*a) ; h = (r*r - z*z - ((j*j)/(a*a))) * ((a*a)/(b*b + a*a)) ; e = sqrt(h + d*d) ; // ?? if( ) return false ; y0 = -d - e ; y1 = -d + e ; x0 = (-b * y0 - j) / a ; x1 = (-b * y1 - j) / a ; SunSetLon = atan2(y1,x1) ; // -pi ... +pi SunRisLon = atan2(y0,x0) ; // ?? ris=0 set=1 ?? or must distinguish now return true ; } Back to top Jim Davis Guest Posted: Sat May 12, 2007 6:29 am    Post subject: Re: Earth sunrise math 3 Space Geometry // http://www.geom.uiuc.edu/docs/reference/CRC-formulas/ // 9.4 Relations between ... 3-Space Coordinates Translating above webpage to C++ . // latitude 0 at northpole // longitude is positive east of greenwich // camera in space is "projective transformation" Where is C source for 3 Space Geometry ? 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