REM A display of our night sky
REM 
REM It requires databases of the form:
REM StarID XPOS  YPOS  ZPOS  Abs Magnitude
REM ********************************************************
skyview()
exit

sub skyview()
nstars=0
local starsky(35000,5)
local skyfield(5000,3)
FOVsky=20
clear screen
open window 400, 300
fill clear rectangle 20, 40 to 375, 400
Text 30, 100, "Stellar Databases"
rectangle 25,103 to 300, 220
rectangle 27, 105 to 298,218
text 30, 130, "1--  Small  -  1,400 stars (fast)"
text 30, 170,"2--  Medium  -  12,000 stars "
do
TEXT 20, 275, "Please Select a database"
db$=inkey$(1)
fill clear rectangle 10, 275 to 200, 250
if (db$<>"") break
db$=inkey$(1)
if (db$<>"") break
loop
close window
stardb=open("subset.dat", "r")
switch db$
case "1":stardb=open("subset.dat", "r"):break
case "2":stardb=open("star.dat", "r"):break
end switch$
Print "LOADING DATABASE"
while(!eof(stardb))
  nstars=nstars+1
  for a=1 to 5:input #stardb starsky(nstars,a):next a
wend
close stardb
sDEC=0
sRA=0  
CLEAR SCREEN
open window 550, 570
circle 97,552,2
circle 191,552,2
text 10, 565, "Arrow keys= 5         A,S,Z,W = 1         + = zoom in     - = zoom out"
Text 445, 565, "esc = quit"
 rectangle 9, 19 to 541, 541
 rectangle 10, 20 to 540, 540
leave=false
goto begin
label start
direct$=inkey$
 fill clear rectangle 0, 19 to 550, 0
switch direct$:
case "right": sRA=sRA-5:break 
case "left": sRA=sRA+5:break
case "up": sDEC=sDEC-5:break
case "down":sDEC=sDEC+5:break

case "s": sRA=sRA-1:break 
case "a": sRA=sRA+1:break
case "w": sDEC=sDEC-1:break
case "z":sDEC=sDEC+1:break
case "S": sRA=sRA-1:break 
case "A": sRA=sRA+1:break
case "W": sDEC=sDEC-1:break
case "Z":sDEC=sDEC+1:break

case "-":FOVsky=FOVsky+1:break
case "=":FOVsky=FOVsky-1:break
case "esc": leave=true:break
end switch
if leave goto ending
label begin
   solRA=sRA*3.1415/180
   solDEC=sDEC*3.1415/180
   fovsky=FOVsky*pi/180
  x=cos(solRA)*cos(solDEC)
  y=sin(solRA)*cos(solDEC)
  z=sin(solDEC)
  Text 215, 20, "RA: ": Text 245, 20, str$(sRA)
  Text 10, 20, "Decl: ": Text 50, 20, str$(sDEC)
  Text 415, 20, "stars: ":  Text 455, 20, str$(skycount)
  Text 300, 20, "FOV: ":Text 335,20, str$(FOVsky)
  magxyz=sqrt(x^2+y^2+z^2)
skycount=0
  For target= 1 to nstars
xtarg=starsky(target,3):ytarg=starsky(target,2):ztarg=starsky(target,4)
ax=(xtarg*x+ytarg*y+ztarg*z)/magxyz
theta=acos((ax/sqrt(xtarg^2+ytarg^2+ztarg^2)))
if (abs(theta)<1.5*fovsky) then
  ay=(xtarg*y-ytarg*x)/sqrt(y^2+x^2)
  az=(xtarg*x*z+ytarg*z*y-ztarg*(x^2+y^2))/sqrt(x*x*z*z+(x*x+y*y)^2+y*y*z*z)
  distance=sqrt(xtarg^2+ytarg^2+ztarg^2)
  RA=atan(ay/ax)
  Decl=atan(az,sqrt(ax^2+ay^2))
    if ((abs(RA)<fovsky) and (abs(Decl)<fovsky)and ax>0) then
        skycount=skycount+1
        skyfield(skycount,1)=-RA
        skyfield(skycount,2)=-Decl
  
skyfield(skycount,3)=starsky(target,5)-5+5*log(distance)/log(10)
     if (skyfield(skycount,3)>6) skyfield(skycount,3)=6
    endif
 endif
  next target

fill rectangle 11, 21 to 539, 539
clear circle 500, 62, 40
clear circle 500, 62, 25
clear line 500-40*cos(4*solRA),62-40*sin(4*solRA) to 500+40*cos(4*solRA),62+40*sin(4*solRA)
clear line 500-40*cos(4*solRA+pi/6),62-40*sin(4*solRA+pi/6) to 500+40*cos(4*solRA+pi/6),62+40*sin(4*solRA+pi/6)
fill circle 500, 62, 24
clear line 500-25*cos(4*solDEC),62-25*sin(4*solDEC) to 500+25*cos(4*solDEC),62+25*sin(4*solDEC)
clear line 500-25*cos(4*solDEC+pi/6),62-25*sin(4*solDEC+pi/6) to 500+25*cos(4*solDEC+pi/6),62+25*sin(4*solDEC+pi/6)
clear circle 500, 62, 14
fill circle 500, 62, 13
CLEAR CIRCLE 500,62, FOVsky/3
clear circle 500,62,FOVsky/6

 for a=1 to skycount
      size=6-skyfield(a,3)
    clear dot 275+250*skyfield(a,1)/fovsky, 275-250*skyfield(a,2)/fovsky
 fill clear circle 275+250*skyfield(a,1)/fovsky, 275-250*skyfield(a,2)/fovsky, size
       next a   
goto start
label ending
close window
end sub