curve_section(values,ncfile,varn)
values= [kindcurve]: kind of curve to follow
  'gridline',[xdimn],[ydimn],[iBL],[jBL],[iUR],[jUR],[Ncurve]: line from starting `bottom-left' grid
    point [iBL],[jBL] to `right-up' grid point [iUR],[jUR] and [Ncurve] number of
    line-points with [xdimn],[ydimn] name of the x and y dimensions
  'lonlatline',[londimn]|[lonvarname],[latdimn]|[latvarname],[lonSW],[latSW],[lonNE],[latNE],[Ncurve]:
    line from starting `SW' lonlat point [lonSW],[latSW] to `NE' lonlat point [lonNE],[latNE]
    and [Ncurve] line-points with '[lon/latdimn]|[lon/latvarn]' name of the dimension and
    variable-dimension of longitude and latitude
  'gridfilecurve',[xdimn],[ydimn],[curvefile]: curve following grid-values in the file
    [curvefile](x y; two columns space separated, '#' commment) with [xdimn],[ydimn] name of
    the x and y dimensions
  'lonlatfilecurve',[londimn]|[lonvarname],[latdimn]|[latvarname],[curvefile]: curve following
    lonlat-values in the file [curvefile](lon lat; two columns space separated, '#' commment)
    'with [lon/latdimn]|[lon/latvarn]' name of the dimension and variable-dimension of longitude
    and latitude
ncfile= name of the file with the variable to fill
varn= name of the variable to get ('all', for all variables)