csc2s

Converts Cartesian coordinates on a unit sphere to spherical coordinates (lat/lon).

Prototype

	function csc2s (
		x  : numeric,  
		y  : numeric,  
		z  : numeric   
	)

	return_val [2,dimsizes(x)] :  float or double

Arguments

Cartesian coordinates on a unit sphere. These variables can have any number of dimensions, but all must have the same number of dimensions and dimension sizes.

Return value

An array of latitudes and longitudes having first dimension 2 and other dimensions agreeing in number and size with those of the input arrays. The latitude values will have a first index of 0 and the longitude values a first index of 1.

If either of the input arrays is double, the output array will be double; in all other cases, the output array will be float.

If any input x, y, or z is a missing value, both the corresponding returned latitude and longitude will have a value calculated in the following way: it will be the value set for the parameter MVL if it has been set (see cssetp for how to set parameter values); or the value of x@_FillValue if x is a missing value; or the value of y@_FillValue if either x@_FillValue is not set or the value for x is not a missing value; or the value of z@_FillValue if either x@_FillValue is not set or the value for x is not a missing value and if either y@_FillValue is not set or the value for y is not a missing value.

The default value for the MVL parameter is -8.; this is used simply as a flag to verify if a value has been set for that parameter.

Description

csc2s converts Cartesian coordinates on a unit sphere to lat/lon coordinates on a sphere. All latitude and longitude coordinates are expressed in degrees. The point at 0 degrees latitude and 0 degrees longitude is identified with Cartesian coordinate (1.,0.,0.).

This function is in the Cssgrid package - a software package that implements a tension spline interpolation algorithm to fit a function to input data randomly spaced on a sphere.

The general documentation for Cssgrid contains complete examples for entries in the package.

See Also

cssgrid, cssgrid_Wrap, csstri, csvoro, css2c, csc2s, cssetp, csgetp

Examples

begin

;
;  Specify the value to be returned when a missing value
;  is encountered in the input.
;
  missing_val_return = -100.5
  cssetp("mvl", missing_val_return)

  rlat = new((/2,5/),integer)

;
;  Define rlat that contains a missing value.
;
;  In NCL versions 5.2.x and earlier, the "new" function sets a 
;  default missing value integer missing value of -999.
;  In versions 6.0.0 and greater, this value is -2147483647.
;
  imsg = -2147483647     ; In v6.0.0, can use 
                         ; imsg = default_value("integer")
                         ; to get default.
  rlat = (/                                          \
           (/ -89, -45, imsg,  45 ,  89 /),     \
           (/  89,  45,    0, -45 , -89 /)      \
         /)

  rlon = (/                                     \
           (/-179., -90., 0., 90., 179./),      \
           (/ 179.,  90., 0.,-90.,-179./)       \
         /)

; 
;   Convert the lat/lon input to Cartesian coordinates on the
;   unit sphere.  The _FillValue attribute for rval will be
;   set to missing_val_return on return.
;  
  rval = css2c(rlat, rlon)
  print(rval)

; 
;   Extract the x, y, and z coordinates of the Cartesian coordinates
;   as arrays.  
; 
  x = rval(0,:,:)
  y = rval(1,:,:)
  z = rval(2,:,:)

  print(x)
  print(y)
  print(z)
  
;
;  Do the reverse transformation.
;
  sval = csc2s(x,y,z)
  print(sval)

end