LAT_SIN (Mar95)                  suntrans                  LAT_SIN (Mar95)



NAME
    LAT_SIN --  interpolates  entire-sphere  images  on  a  heliographic
    coordinate   system   which  are  equally  spaced  in  latitude  and 
    longitude  onto  partial-sphere  folded  images  on  a  heliographic 
    coordinate  system  which are equally spaced in longitude and either
    sin(latitude) or latitude.
    
    
USAGE
    lat_sin inputl outputl trim_file (interp_kind npole_wrap)
    
    
PARAMETERS
    
    inputl
        input image or list of images
    
    outputl
        output image or list of images
    
    trim_file
        binary   file   containing   the    specifications    for    the  
        latitude-longitude  grid  and the corresponding mode coefficient
        trimming limits.  This  required  input  file  is  generated  by
        PLMTRIM  and  may  be  used  reused for all images with the same
        latitude-longitude grid parameters and maximum l value.
    
    (interp_kind = poly3)
        type of interpolation for use on the solar disk.  The  available
        interpolators    are    nearest   (nearest   neighbor),   linear  
        (bilinear),  poly3  (bicubic),  poly5  (biquintic)  and  spline3 
        (bicubic  spline).   The interpolators are discussed in the help
        files in the iraf directory /math/iminterp/doc.
    
    (npole_wrap = 0)
        number of lines to extend the array at  the  poles  for  use  in
        interpolating  very  close  to  the  poles.   Each  meridian  of 
        longitude is extended by using the meridian 180  degrees  across
        from it in reverse order.
    
    
IMAGE HEADER WORDS
    
    BEGNLONG
        heliographic longitude of the first x pixel (first subscript)
    
    BEGNLAT
        heliographic latitude of the first y pixel (second subscript)
    
    DLONG
        spacing in heliographic longitude of the x pixels
    
    DLAT
        spacing in heliographic latitude of the y pixels
    
    
DESCRIPTION
    Task  HENTERP  interpolates  data  evenly  spaced  in  latitude  and 
    longitude to the latitude-longitude grid specified in  the  trimming
    limit  file.   HENTERP  is  equiped to reflect lines of pixels about
    the pole to allow interpolation near the poles, but is not  equipped
    to  interpolate  across  the  longitude  bounds  of  the input image
    grid.  If  piecing  of  an  image  over  the  input  image  boundary
    longitudes  is  required,  the user needs to prepare the input image
    for this type of interpolation by shifting or replicating the  image
    before  interpolation.   The output image is written in folded image
    format.
    
    
EXAMPLES
    
    1.   imagein  is  interpolated  on   the   latitude-longitude   grid 
    specified  in  the  trimming limit file, mod250.dat, and the results
    written into imageout.
    
            su> henterp imagein imageout mod250.dat
    
    2.   The  images  listed  in  input.lis  are  interpolated  on   the 
    latitude-longitude  grid  specified  in  the  trimming  limit  file, 
    mod250.dat, and the results written into the new image files  listed
    in   output.lis.   The  latitude-longitude  grid  specified  in  the 
    trimming limit file, mod250.dat,  requires  interpolation  near  the
    pole,  so  the  interpolation  is  performed using 5 lines reflected
    about the poles.
    
            su> henterp @input.lis @output.lis mod250.dat npole_wrap=5
    
    3.   imagein  is  interpolated  on   the   latitude-longitude   grid 
    specified  in the trimming limit file, mod250.dat, using the bicubic
    spline interpolator.  The result is written into imageout.
    
            su> henterp imagein imageout mod250.dat interp_kind=spline3
    
    
    
TIME REQUIREMENTS
    On a per image basis, the latitude-longitude interpolation  consumes
    about  2 seconds of cpu time and about 5 seconds of elapsed time per
    image  on  the  DECstation  3100.     Use  of   a   bicubic   spline 
    interpolator  increases  the  time  requirement  by about 10% on the
    DECstation  3100.
    
    
BUGS
    None known.
    
    
SEE ALSO
    plm_trim
    
    helio_image