# Coordinates Conversion Program II

The following program converts from latitude and longitude coordinates to polar stereographic SSM/I grid coordinates to pixel sample lines and indexes. Program I converts from pixel sample and line indexes to polar stereographic SSM/I grid coordinates to latitude and longitude coordinates.

```c      Convert_11_xy
c
c      This program converts from latitude and longitude
c      to polar stereographic SSM/I grid coordinates (in km)
c      and to Leads ARI grid sample,line indexes.  This program is a
c      version of the program written by C.S. Morris, Jet Propulsion
c      Laboratory,  which appears in the NSIDC SSM/I User's
c      Guide, Section F, "SSMII Polar Grids".
c
c      NOARL Remote Sensing,Stennis Space Center, March 1991

dimension t (2)
real*4 x,y,alat,along
real*8 e,e2,cdr,pi
character*1 grid

c      Conversion constant, degrees to radians:
cdr=57.29577951
c      Radius and eccentricity of earth (Hughes ellipsiod, km):
re=6378.273
e2=0.006693883
e=SQRT(e2)
pi=3.141592654
c      Standard parallel - latitude of no distortion
slat=70.0
c      Puts 135 deg long. at the top of the grid:
xlam=-45.

print*,'Type ''P'' for Pacific grid, ''E'' for European'
accept*,grid
100    print*,'Type latitude, longitude (9999,9999 to stop)'
accept*,alat,along
if (alat.eq.9999.) goto 999
if(alat.lt.89.995)goto 250
x=0.
y=0.
goto  300
250    rlat=alat
do 600 II=1,2
if(II.eq.2)rlat=slat
600    t(II)=TAN((pi/4.)-(rlat/(2.*cdr)))/((1.-e*SIND(rlat))/
& (1.+e*SIND(rlat)))**(e/2.)

cm=COSD(slat)/SQRT(1.-e2*(SIND(slat)**2))
rho-re*cm*t(1)/t(2)
x=rho*SIND(along-xlam)
y=rho*COSD(along-xlam)
c      Transform sample, line coordinates to SSMI grid coordinates
300    if(grid.eq.'P'.or.grid.eq.'p')then
rline=1975-y
sample=x+2250
else
rline=1300-y
sample=x
end if
print*,'    Sample    Line       SSMI x      SSMI y    Lat
&       Long'
write (6,310)sample,rline,x,y,alat,along
print*
goto  100
310    format(4f1O.2,2f1O.4)
999    continue
end
```

The program is taken from:
Fetterer and Hawkins. 1991. An AVHRR data set for the Arctic leads ARI. Naval Oceanographic and Atmospheric Research Laboratory, Technical Note 118. 61 p.