LATLON2XY is the jSphere module of jLab.

  LATLON2XY  Converts latitude and longitude into tangent plane coordinates.
    [X,Y]=LATLON2XY(LAT,LON,LATO,LONO) converts (LAT,LON) with units of
    degrees into displacements (X,Y) in a plane tangent to the earth at the
    point (LATO, LONO). X and Y have units of kilometers.
    CX=LATLON2XY(LAT,LON,LATO,LONO) with one output argument returns the 
    location as a complex-valued quantity X+SQRT(-1)*Y. NANs in LAT or LON
    become NAN+SQRT(-1)*NAN.
    LAT and LON are arrays of the same size.  LATO and LONO are either also
    arrays of this size, or else scalars.  X and Y have the same size as 
    the input arrays.  
    X and Y are computed by projecting the tangent plane onto the sphere
    using full spherical geometry, see Lilly and Lagerloef (2018).  
    Note that X and Y are set to NANs for points on the opposite side of
    the earth from the tangent plane, that is, where the great circle 
    distance would exceed RADEARTH * pi/2.  
    Great circle distance
    [X,Y,D]=LATLON2XY(...) also returns the great circle distance D between
    the two sets of points.  
    LATLON2XY gives the same distance as SPHEREDIST for points where the 
    great circle distance is less than RADEARTH * pi/2, but returns NaNs
    for greater distances.
    The great circle distance returned here is useful because it is a fast 
    computation if X and Y are already known.
    Cell array input / output
    LATLON2XY returns cell array output given cell array input.  
    That is, if LAT, LON, LATO, and LONO are all cell arrays of length K, 
    containing K different numerical arrays, then the output will also be 
    cell arrays of length K.  
    This also works if LAT and LON are cell arrays but LATO and LONO are 
    Small angle approximation
    [X,Y,D]=LATLON2XY(...,'small') returns X, Y, and D based on the small 
    angle approximation, corrected for points differing in longitude by 
    more than ninety degrees.  See Lilly and Lagerloef (2018) for details.
    This is primarily used for testing purposes. 
    LATLON2XY is inverted by XY2LATLON.
    'latlon2xy --t' runs some tests.
    Usage:  [x,y]=latlon2xy(lat,lon,lato,lono);
    This is part of JLAB --- type 'help jlab' for more information
    (C) 2000--2018 J.M. Lilly --- type 'help jlab_license' for details

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