Table of contents
CSPICE_RECAZL converts rectangular coordinates of a point to range,
azimuth and elevation.
Given:
rectan the rectangular coordinates of a point.
help, rectan
DOUBLE = Array[3]
azccw a flag indicating how azimuth is measured.
help, azccw
BOOLEAN = Scalar
If `azccw' is True, azimuth increases in the
counterclockwise direction; otherwise it increases in
the clockwise direction.
elplsz a flag indicating how elevation is measured.
help, elplsz
BOOLEAN = Scalar
If `elplsz' is True, elevation increases from
the XY plane toward +Z; otherwise toward -Z.
the call:
cspice_recazl, rectan, azccw, elplsz, range, az, el
returns:
range the distance of the point from the origin.
help, range
DOUBLE = Scalar
The units associated with `range' are those associated
with the input point.
az the azimuth of the point.
help, az
DOUBLE = Scalar
This is the angle between the projection onto the XY plane of
the vector from the origin to the point and the +X axis of
the reference frame. `az' is zero at the +X axis.
The way azimuth is measured depends on the value of the
logical flag `azccw'. See the description of the argument
`azccw' for details.
`az' is output in radians. The range of `az' is [0, 2*pi].
el the elevation of the point.
help, el
DOUBLE = Scalar
This is the angle between the vector from the origin to the
point and the XY plane. `el' is zero at the XY plane.
The way elevation is measured depends on the value of
the logical flag `elplsz'. See the description of the
argument `elplsz' for details.
`el' is output in radians. The range of `el' is [-pi/2, pi/2].
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) Create four tables showing a variety of rectangular
coordinates and the corresponding range, azimuth and
elevation, resulting from the different choices of the `azccw'
and `elplsz' flags.
Corresponding rectangular coordinates and azimuth, elevation
and range are listed to three decimal places. Output angles
are in degrees.
Example code begins here.
PRO recazl_ex1
;;
;; Local parameters.
;;
NREC = 11L
SPICEFALSE = 0B
SPICETRUE = 1B
;;
;; Define the input rectangular coordinates and the
;; different choices of the `azccw' and `elplsz' flags.
;;
rectan = [ [0.D0,0.D0,0.D0], [1.D0,0.D0,0.D0], [0.D0,1.D0,0.D0], $
[0.D0,0.D0,1.D0], [-1.D0,0.D0,0.D0], [0.D0,-1.D0,0.D0], $
[0.D0,0.D0,-1.D0], [1.D0,1.D0,0.D0], [1.D0,0.D0,1.D0], $
[0.D0,1.D0,1.D0], [1.D0,1.D0,1.D0] ]
azccw = [SPICEFALSE, SPICETRUE]
elplsz = [SPICEFALSE, SPICETRUE]
;;
;; Create a table for each combination of `azccw' and `elplsz'.
;;
for i=0L, 1L do begin
for j=0L, 1L do begin
;;
;; Display the flag settings.
;;
msg = 'AZCCW = #; ELPLSZ = #'
cspice_repml, msg, '#', azccw[i], 'C', msg
cspice_repml, msg, '#', elplsz[j], 'C', msg
print
print, format='(A)', msg
;;
;; Print the banner.
;;
print
print, format='(A)', ' rect[0] rect[1] rect[2] ' + $
' range az el'
print, format='(A)', ' ------- ------- ------- ' + $
' ------- ------- -------'
;;
;; Do the conversion. Output angles in degrees.
;;
for n=0L, NREC-1L do begin
cspice_recazl, rectan[*,n], azccw[i], elplsz[j], $
range, az, el
print, format='(6F9.3)', rectan[*,n], range, $
az * cspice_dpr(), $
el * cspice_dpr()
endfor
endfor
endfor
END
When this program was executed on a Mac/Intel/IDL8.x/64-bit
platform, the output was:
AZCCW = False; ELPLSZ = False
rect[0] rect[1] rect[2] range az el
------- ------- ------- ------- ------- -------
0.000 0.000 0.000 0.000 0.000 0.000
1.000 0.000 0.000 1.000 0.000 0.000
0.000 1.000 0.000 1.000 270.000 0.000
0.000 0.000 1.000 1.000 0.000 -90.000
-1.000 0.000 0.000 1.000 180.000 0.000
0.000 -1.000 0.000 1.000 90.000 0.000
0.000 0.000 -1.000 1.000 0.000 90.000
1.000 1.000 0.000 1.414 315.000 0.000
1.000 0.000 1.000 1.414 0.000 -45.000
0.000 1.000 1.000 1.414 270.000 -45.000
1.000 1.000 1.000 1.732 315.000 -35.264
AZCCW = False; ELPLSZ = True
rect[0] rect[1] rect[2] range az el
------- ------- ------- ------- ------- -------
0.000 0.000 0.000 0.000 0.000 0.000
1.000 0.000 0.000 1.000 0.000 0.000
0.000 1.000 0.000 1.000 270.000 0.000
0.000 0.000 1.000 1.000 0.000 90.000
-1.000 0.000 0.000 1.000 180.000 0.000
0.000 -1.000 0.000 1.000 90.000 0.000
0.000 0.000 -1.000 1.000 0.000 -90.000
1.000 1.000 0.000 1.414 315.000 0.000
1.000 0.000 1.000 1.414 0.000 45.000
0.000 1.000 1.000 1.414 270.000 45.000
1.000 1.000 1.000 1.732 315.000 35.264
AZCCW = True; ELPLSZ = False
rect[0] rect[1] rect[2] range az el
------- ------- ------- ------- ------- -------
0.000 0.000 0.000 0.000 0.000 0.000
1.000 0.000 0.000 1.000 0.000 0.000
0.000 1.000 0.000 1.000 90.000 0.000
0.000 0.000 1.000 1.000 0.000 -90.000
-1.000 0.000 0.000 1.000 180.000 0.000
0.000 -1.000 0.000 1.000 270.000 0.000
0.000 0.000 -1.000 1.000 0.000 90.000
1.000 1.000 0.000 1.414 45.000 0.000
1.000 0.000 1.000 1.414 0.000 -45.000
0.000 1.000 1.000 1.414 90.000 -45.000
1.000 1.000 1.000 1.732 45.000 -35.264
AZCCW = True; ELPLSZ = True
rect[0] rect[1] rect[2] range az el
------- ------- ------- ------- ------- -------
0.000 0.000 0.000 0.000 0.000 0.000
1.000 0.000 0.000 1.000 0.000 0.000
0.000 1.000 0.000 1.000 90.000 0.000
0.000 0.000 1.000 1.000 0.000 90.000
-1.000 0.000 0.000 1.000 180.000 0.000
0.000 -1.000 0.000 1.000 270.000 0.000
0.000 0.000 -1.000 1.000 0.000 -90.000
1.000 1.000 0.000 1.414 45.000 0.000
1.000 0.000 1.000 1.414 0.000 45.000
0.000 1.000 1.000 1.414 90.000 45.000
1.000 1.000 1.000 1.732 45.000 35.264
2) Compute the apparent azimuth and elevation of Venus as seen
from the DSS-14 station.
Task Description
================
In this example, we will obtain the apparent position of
Venus as seen from the DSS-14 station in the DSS-14 topocentric
reference frame. We will use a station frames kernel and
transform the resulting rectangular coordinates to azimuth,
elevation and range using cspice_azlrec.
In order to introduce the usage of the logical flags `azccw'
and `elplsz', we will request the azimuth to be measured
clockwise and the elevation positive towards the +Z
axis of the DSS-14_TOPO reference frame.
Kernels
=======
Use the meta-kernel shown below to load the required SPICE
kernels.
KPL/MK
File name: recazl_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
--------- --------
de430.bsp Planetary ephemeris
naif0011.tls Leapseconds
earth_720101_070426.bpc Earth historical
binary PCK
earthstns_itrf93_050714.bsp DSN station SPK
earth_topo_050714.tf DSN station FK
\begindata
KERNELS_TO_LOAD = ( 'de430.bsp',
'naif0011.tls',
'earth_720101_070426.bpc',
'earthstns_itrf93_050714.bsp',
'earth_topo_050714.tf' )
\begintext
End of meta-kernel.
Example code begins here.
PRO recazl_ex2
;;
;; Local parameters
;;
FMT0 = '(3F21.8)'
FMT1 = '(A,F20.8)'
META = 'recazl_ex2.tm'
SPICEFALSE = 0B
SPICETRUE = 1B
;;
;; Load SPICE kernels.
;;
cspice_furnsh, META
;;
;; Convert the observation time to seconds past J2000 TDB.
;;
obstim = '2003 OCT 13 06:00:00.000000 UTC'
cspice_str2et, obstim, et
;;
;; Set the target, observer, observer frame, and
;; aberration corrections.
;;
target = 'VENUS'
obs = 'DSS-14'
ref = 'DSS-14_TOPO'
abcorr = 'CN+S'
;;
;; Compute the observer-target position.
;;
cspice_spkpos, target, et, ref, abcorr, obs, ptarg, ltime
;;
;; Compute azimuth, elevation and range of Venus
;; as seen from DSS-14, with azimuth increasing
;; clockwise and elevation positive towards +Z
;; axis of the DSS-14_TOPO reference frame
;;
azccw = SPICEFALSE
elplsz = SPICETRUE
cspice_recazl, ptarg, azccw, elplsz, r, az, el
;;
;; Express both angles in degrees.
;;
el = el * cspice_dpr()
az = az * cspice_dpr()
;;
;; Display the computed position, the range and
;; the angles.
;;
print
print, format='(2A)', 'Target: ', target
print, format='(2A)', 'Observation time: ', obstim
print, format='(2A)', 'Observer center: ', obs
print, format='(2A)', 'Observer frame: ', ref
print, format='(2A)', 'Aberration correction: ', abcorr
print
print, format='(A)', 'Observer-target position (km):'
print, format=FMT0, ptarg
print, format=FMT1, 'Light time (s): ', ltime
print
print, format=FMT1, 'Target azimuth (deg): ', az
print, format=FMT1, 'Target elevation (deg): ', el
print, format=FMT1, 'Observer-target distance (km): ', r
print
;;
;; It's always good form to unload kernels after use,
;; particularly in IDL due to data persistence.
;;
cspice_kclear
END
When this program was executed on a Mac/Intel/IDL8.x/64-bit
platform, the output was:
Target: VENUS
Observation time: 2003 OCT 13 06:00:00.000000 UTC
Observer center: DSS-14
Observer frame: DSS-14_TOPO
Aberration correction: CN+S
Observer-target position (km):
66886767.37916669 146868551.77222887 -185296611.10841593
Light time (s): 819.63862811
Target azimuth (deg): 294.48543372
Target elevation (deg): -48.94609726
Observer-target distance (km): 245721478.99272084
This routine returns the range, azimuth, and elevation of a point
specified in rectangular coordinates.
The output is defined by the distance from the center of the
reference frame (range), the angle from a reference vector
(azimuth), and the angle above the XY plane of the reference
frame (elevation).
The way azimuth and elevation are measured depends on the values
given by the user to the `azccw' and `elplsz' logical flags. See the
descriptions of these input arguments for details.
1) If the X and Y components of `rectan' are both zero, the
azimuth is set to zero.
2) If `rectan' is the zero vector, azimuth and elevation
are both set to zero.
3) If any of the input arguments, `rectan', `azccw' or `elplsz',
is undefined, an error is signaled by the IDL error handling
system.
4) If any of the input arguments, `rectan', `azccw' or `elplsz',
is not of the expected type, or it does not have the expected
dimensions and size, an error is signaled by the Icy
interface.
5) If any of the output arguments, `range', `az' or `el', is not
a named variable, an error is signaled by the Icy interface.
None.
None.
ICY.REQ
None.
J. Diaz del Rio (ODC Space)
-Icy Version 1.0.0, 01-NOV-2021 (JDR)
rectangular coordinates to range, az and el
rectangular to range, azimuth and elevation
convert rectangular coordinates to range, az and el
convert rectangular to range, azimuth and elevation
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