;docformat = 'rst' ;+ ;Given a time, heliocentric latitude and longitude of point on Sun, ;calculate the corresponding alpha angle, and beta angle from the center of the solar disk. Both take ;into account B0 "nodding" of Sun ; ;:Params: ; jd: in, required ; Julian Date of observation, UTC, TAI, TT, doesn't matter. This function ; is not accurate enough to differentiate. ; lat_: in, required ; Heliocentric latitude in degrees ; lon_: in, required ; Heliocentric longitude in degrees, 0deg through sub-earth point ;:Keywords: ; Alpha: out, required ; Horizontal angle from center of solar disk, arcmin, positive east "left" ; on published sam images ; Beta: out, required ; Vertical angle from center of solar disk, arcmin, positive north "up" on ; published sam images ;:Categories: ; utility ;- pro sam_ll_to_ab,jd,lat_,lon_,alpha=alpha,beta=beta ;Solar almanac rs=697500d; km, surface of transition region 2000km above photosphere radius 695500km junk=eve_sun_almanac(jd,R=R,B0=B0) r_1au=r*1.49597870691d8; km, center of sun to center of Earth ;Heliocentric vector lat=lat_*!dpi/180d lon=lon_*!dpi/180d rrs=rs*[cos(lat)*cos(-lon),cos(lat)*sin(-lon),sin(lat)] ;Rotate into SNR (around SNR Y axis) c=cos(B0); s=sin(B0); rrs2=[c*rrs[0]-s*rrs[2],rrs[1],s*rrs[0]+c*rrs[2]] rrs=rrs2 t_alp=rrs[1]/rrs[0]; t_bet=rrs[2]/rrs[0]; alpha=60d*180d*atan(t_alp)/!dpi beta=60d*180d*atan(t_bet)/!dpi end