Telescope Pointing Utilities¶
jwst.lib.set_telescope_pointing Module¶
Set Telescope Pointing from Observatory Engineering Telemetry
Calculate and update the pointingrelated and world coordinate systemrelated keywords. Given a time period, usually defined by an exposure, the engineering mnemonic database is queried for observatory orientation. The orientation defines the sky coordinates a particular point on the observatory is pointed to. Then, using a set of matrix transformations, the sky coordinates of the reference pixel of a desired aperture is calculated.
The transformations are defined by the Technical Reference JWSTSTScI003222, SM12. This document has undergone a number of revisions. The current version implemented is based on an internal email version Rev. C, produced 202111.
There are a number of algorithms, or methods, that have been implemented.
Most represent the historical refinement of the algorithm. Until the technical
reference is finalized, all methods will remain in the code. The default,
stateofthe art algorithm is represented by method OPS_TR_202111
,
implemented by
calc_transforms_ops_tr_202111
.
Interface¶
The primary usage is through the command line interface
set_telescope_pointing.py
. Operating on a list of JWST Level 1b exposures,
this command updates the world coordinate system keywords with the values
necessary to translate from aperture pixel to sky coordinates.
Access to the JWST Engineering Mnemonic database is required. See the Engineering Database Interface for more information.
Programmatically, the command line is implemented by the function
add_wcs
, which calls the basic function
calc_wcs
. The available methods are defined
by Methods
.
There are two data structures used to maintain the state of the transformation.
TransformParameters
contains the parameters
needed to perform the transformations.
Transforms
contains the calculated
transformation matrices.
Transformation Matrices¶
All the transformation matrices, as defined by
Transforms
, are Direction Cosine Matrices
(DCM). A DCM contains the Euler rotation angles that represent the sky
coordinates for a particular frameofreference. The initial DCM is provided
through the engineering telemetry and represents where in the sky either the
Fine Guidance Sensor (FGS) or star tracker is pointed to. Then, through a set
of transformations, the DCM for the reference point of the target aperture
is calculated.
Functions¶

Add WCS information to a JWST DataModel. 

Calculate transforms which determine reference point celestial WCS 

Calculate transforms in OPS using TR 202111 

Given observatory orientation and target aperture, calculate V1 and Reference Pixel sky coordinates 

Calculate V1 and WCS over a time period 

Update WCS pointing information 
Classes¶

Available methods to calculate V1 and aperture WCS information 

Parameters required the calculations 

The matrices used in calculation of the M_eci2siaf transformation 

Create new instance of WCSRef(ra, dec, pa) 
jwst.lib.v1_calculate Module¶
V1 Calculation based on time and engineering database info
Functions¶

Calculate V1 over the time period for the given models 

Calculate V1 over the given time period 
Commands¶
Available commands are as follows. Use the h
option for more details.
 set_telescope_pointing.py
Update basic WCS information in JWST exposures from the engineering database.
 pointing_summary
Summarize various pointing information in a table.
 v1_calculate
Calculate V1 over a time period.