chandra_aca.centroid_resid

class chandra_aca.centroid_resid.CentroidResiduals(start, stop)

Class to calculate star centroid residuals.

This class is designed to set up and perform the residual calculations on any desired combination of source centroids and source attitudes. For the common use cases, centroids, attitudes, and commanded star positions are retrieved automatically from archived sources.

Based on analysis, time offsets are applied to centroid times by default. See fit notebooks in:

http://nbviewer.jupyter.org/url/cxc.harvard.edu/mta/ASPECT/ipynb/centroid_time_offsets/OR.ipynb

and

http://nbviewer.jupyter.org/url/cxc.harvard.edu/mta/ASPECT/ipynb/centroid_time_offsets/ER.ipynb

Users should see the class method for_slot for a convenient way to get centroid residuals on an obsid for an ACA slot (aka image number).

Example usage:

>>> import numpy as np
>>> from chandra_aca.centroid_resid import CentroidResiduals
>>> cr = CentroidResiduals.for_slot(obsid=20001, slot=5)
>>> np.max(np.abs(cr.dyags))
0.87602233734844503
>>> np.max(np.abs(cr.dzags))
1.2035827855862777
>>> cr.atts[0]
array([-0.07933254,  0.87065874, -0.47833673,  0.08278696])
>>> cr.agasc_id
649201816

This example calculates the residuals on slot 5 of obsid 20001 using the ground aspect solution and ground centroids. Here is another example that does the same thing without using the for_slot convenience.

Example usage:

>>> import numpy as np
>>> from chandra_aca.centroid_resid import CentroidResiduals
>>> cr = CentroidResiduals(start='2017:169:18:54:50.138', stop='2017:170:05:13:58.190')
>>> cr.set_atts('ground')
>>> cr.set_centroids('ground', slot=5)
>>> cr.set_star(agasc_id=649201816)
>>> cr.calc_residuals()
>>> np.max(np.abs(cr.dyags))
0.87602233734844503

Parameters:

• start – start time of interval for residuals (DateTime compatible)

• stop – stop time of interval for residuals (DateTime compatible)

calc_residuals()

Calculate star residuals.

Calculate residuals based on attitude and ra/dec of star. Note that the sampling and times of yags may be different from zags so these should be done independently.

Residuals are available in self.dyags and self.dzags. Predicted values from attitude and star position in self.pred_yags and self.pred_zags

set_atts(source)

Get attitude solution quaternions from source.

One could also just set atts and att_times attributes directly.

set_centroids(source, slot, alg=8, apply_dt=True)

Assign centroids.

Assign centroids from source and slot to the objects centroid attributes (yag, zag, yag_times, zag_times)

For the supported sources (ground, obc) the centroids are fetched from the mica L1 archive or telemetry.

yag, zag, yag_times an zag_times can also be set directly without use of this method.

Parameters:

source

‘ground’ | ‘obc’

slot

ACA slot

alg

for ground processing, use centroids from this algorithm.

apply_dt

apply centroid time offsets via ‘set_offsets’

set_offsets()

Apply time offsets to centroids.

Apply time offsets to centroids based on type and source of centroid, obsid (suggesting 8x8 or 6x6 data), telemetry source (‘maude’ or ‘cxc’) and aspect solution source. These time offsets were fit. See fit notebooks at:

http://nbviewer.jupyter.org/url/cxc.harvard.edu/mta/ASPECT/ipynb/centroid_time_offsets/OR.ipynb

and

http://nbviewer.jupyter.org/url/cxc.harvard.edu/mta/ASPECT/ipynb/centroid_time_offsets/ER.ipynb

set_star(agasc_id=None, slot=None)

Set self.ra and dec from either agasc_id or slot.

This assumes use of star in default agasc miniagasc (no 1.4 or 1.5 or very faint stars) Lookup by “slot” relies on database of starcheck catalogs.

This also sets self.agasc_id.