Table of contents
CSPICE_SPHLAT converts spherical coordinates to latitudinal
coordinates.
Given:
r the distance of the point from the origin.
help, r
DOUBLE = Scalar
colat the angle between the vector from the origin to the point and
the positive Z-axis in radians.
help, colat
DOUBLE = Scalar
slon the angle of the point from the XZ plane (radians).
help, slon
DOUBLE = Scalar
the call:
cspice_sphlat, r, colat, slon, radius, lon, lat
returns:
radius the distance of a point from the origin.
help, radius
DOUBLE = Scalar
lon the angle of the point from the XZ plane in radians.
help, lon
DOUBLE = Scalar
`lon' is set equal to `slon'.
lat the angle of the point from the XY plane in radians.
help, lat
DOUBLE = Scalar
`lat' is computed as pi/2 - colat.
None.
Any numerical results shown for these examples may differ between
platforms as the results depend on the SPICE kernels used as input
and the machine specific arithmetic implementation.
1) Latitude is obtained by subtracting co-latitude from cspice_halfpi
Radius and longitude mean the same thing in both latitudinal
and spherical coordinates. The table below lists `lat' and
corresponding `colat' in terms of degrees.
lat colat
----- -----
0 90
20 70
45 45
-30 120
90 0
-45 135
2) Compute the spherical coordinates of the position of the Moon
as seen from the Earth, and convert them to latitudinal and
rectangular coordinates.
Use the meta-kernel shown below to load the required SPICE
kernels.
KPL/MK
File name: sphlat_ex2.tm
This meta-kernel is intended to support operation of SPICE
example programs. The kernels shown here should not be
assumed to contain adequate or correct versions of data
required by SPICE-based user applications.
In order for an application to use this meta-kernel, the
kernels referenced here must be present in the user's
current working directory.
The names and contents of the kernels referenced
by this meta-kernel are as follows:
File name Contents
--------- --------
de421.bsp Planetary ephemeris
naif0012.tls Leapseconds
\begindata
KERNELS_TO_LOAD = ( 'de421.bsp',
'naif0012.tls' )
\begintext
End of meta-kernel
Example code begins here.
PRO sphlat_ex2
;;
;; Load SPK and LSK kernels, use a meta kernel for
;; convenience.
;;
cspice_furnsh, 'sphlat_ex2.tm'
;;
;; Look up the geometric state of the Moon as seen from
;; the Earth at 2017 Mar 20, relative to the J2000
;; reference frame.
;;
cspice_str2et, '2017 Mar 20', et
cspice_spkpos, 'Moon', et, 'J2000', 'NONE', 'Earth', pos, ltime
;;
;; Convert the position vector `pos' to spherical
;; coordinates.
;;
cspice_recsph, pos, r, colat, slon
;;
;; Convert the spherical coordinates to latitudinal.
;;
cspice_sphlat, r, colat, slon, radius, lon, lat
;;
;; Convert the latitudinal coordinates to rectangular.
;;
cspice_latrec, radius, lon, lat, rectan
print, ' '
print, 'Original rectangular coordinates:'
print, ' '
print, format='(A,F20.8)', ' X (km): ', pos[0]
print, format='(A,F20.8)', ' Y (km): ', pos[1]
print, format='(A,F20.8)', ' Z (km): ', pos[2]
print, ' '
print, 'Spherical coordinates:'
print, ' '
print, format='(A,F20.8)', ' Radius (km): ', r
print, format='(A,F20.8)', ' Colatitude (deg): ', $
colat*cspice_dpr( )
print, format='(A,F20.8)', ' Longitude (deg): ', $
slon*cspice_dpr( )
print, ' '
print, 'Latitudinal coordinates:'
print, ' '
print, format='(A,F20.8)', ' Radius (km): ', radius
print, format='(A,F20.8)', ' Longitude (deg): ', lon*cspice_dpr( )
print, format='(A,F20.8)', ' Latitude (deg): ', lat*cspice_dpr( )
print, ' '
print, 'Rectangular coordinates from cspice_latrec:'
print, ' '
print, format='(A,F20.8)', ' X (km): ', rectan[0]
print, format='(A,F20.8)', ' Y (km): ', rectan[1]
print, format='(A,F20.8)', ' Z (km): ', rectan[2]
print, ' '
END
When this program was executed on a Mac/Intel/IDL8.x/64-bit
platform, the output was:
Original rectangular coordinates:
X (km): -55658.44323296
Y (km): -379226.32931475
Z (km): -126505.93063865
Spherical coordinates:
Radius (km): 403626.33912495
Colatitude (deg): 108.26566077
Longitude (deg): -98.34959789
Latitudinal coordinates:
Radius (km): 403626.33912495
Longitude (deg): -98.34959789
Latitude (deg): -18.26566077
Rectangular coordinates from cspice_latrec:
X (km): -55658.44323296
Y (km): -379226.32931475
Z (km): -126505.93063865
3) Create a table showing a variety of spherical coordinates
and the corresponding cylindrical coordinates.
Corresponding spherical and cylindrical coordinates are
listed to three decimal places. Input and output angles
are in degrees.
Example code begins here.
PRO sphlat_ex3
;;
;; Local parameters.
;;
NREC = 11
;;
;; Define the input spherical coordinates. Angles in
;; degrees.
;;
r = [ 0.0d, 1.0d, 1.0d, 1.0d, 1.4142d, 1.0d, $
1.0d, 1.0d, 1.4142d, 1.0d, 0.0d ]
colat = [ 0.0d, 90.0d, 90.0d, 0.0d, 45.0d, 90.0d, $
180.0d, 90.0d, 135.0d, 0.0d, 90.0d ]
slon = [ 0.0d, 0.0d, 90.0d, 0.0d, 180.0d, -90.0d, $
0.0d, 45.0d, 180.0d, 180.0d, 33.0d ]
;;
;; Print the banner.
;;
print, ' r colat slon radius lon lat'
print, ' ------- ------- ------- ------- ------- -------'
;;
;; Do the conversion. Output angles in degrees.
;;
for i=0, NREC - 1L do begin
rcolat = colat[i] * cspice_rpd( )
rslon = slon[i] * cspice_rpd( )
cspice_sphlat, r[i], rcolat, rslon, radius, lon, lat
print, format='(3F9.3,$)', r[i], colat[i], slon[i]
print, format='(3F9.3)', radius, lon * cspice_dpr(), $
lat * cspice_dpr()
endfor
END
When this program was executed on a Mac/Intel/IDL8.x/64-bit
platform, the output was:
r colat slon radius lon lat
------- ------- ------- ------- ------- -------
0.000 0.000 0.000 0.000 0.000 90.000
1.000 90.000 0.000 1.000 0.000 0.000
1.000 90.000 90.000 1.000 90.000 0.000
1.000 0.000 0.000 1.000 0.000 90.000
1.414 45.000 180.000 1.414 180.000 45.000
1.000 90.000 -90.000 1.000 -90.000 0.000
1.000 180.000 0.000 1.000 0.000 -90.000
1.000 90.000 45.000 1.000 45.000 0.000
1.414 135.000 180.000 1.414 180.000 -45.000
1.000 0.000 180.000 1.000 180.000 90.000
0.000 90.000 33.000 0.000 33.000 0.000
This routine returns the latitudinal coordinates of a point
whose position is input in spherical coordinates.
Latitudinal coordinates are defined by a distance from a central
reference point, an angle from a reference meridian, and an angle
above the equator of a sphere centered at the central reference
point.
Spherical coordinates are defined by a distance from a central
reference point, an angle from a reference meridian, and an angle
from the Z-axis.
1) If any of the input arguments, `r', `colat' or `slon', is
undefined, an error is signaled by the IDL error handling
system.
2) If any of the input arguments, `r', `colat' or `slon', is not
of the expected type, or it does not have the expected
dimensions and size, an error is signaled by the Icy
interface.
3) If any of the output arguments, `radius', `lon' or `lat', is
not a named variable, an error is signaled by the Icy
interface.
None.
None.
ICY.REQ
None.
J. Diaz del Rio (ODC Space)
E.D. Wright (JPL)
-Icy Version 1.1.0, 10-AUG-2021 (JDR)
Edited the header to comply with NAIF standard. Added complete code
examples.
Changed the input argument name "lons" to "slon" for consistency
with other routines.
Added -Parameters, -Exceptions, -Files, -Restrictions,
-Literature_References and -Author_and_Institution sections, and
completed -Particulars section.
Removed reference to the routine's corresponding CSPICE header from
-Abstract section.
Added arguments' type and size information in the -I/O section.
-Icy Version 1.0.1, 09-DEC-2005 (EDW)
Added -Examples section.
-Icy Version 1.0.0, 16-JUN-2003 (EDW)
spherical to latitudinal coordinates
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