Description
newsimulator provides a unified interface for simulation of
telescope processing. It can create a MeasurementSet from scratch or
read in an existing MeasurementSet, it can predict synthesis data onto
the (u,v) coordinates or single dish data onto (ra,dec) points, and it
can corrupt this data through Gaussian errors or through specific
errors residing in (anti-) calibration tables.
newsimulator is substantially different from (and better than)
simulator. Scripts written for one will not work
for the other.
In the observing phase, newsimulator tries to act like a
(simple) telescope. You first make a newsimulator tool, with the
name of the MeasurementSet that you wish to construct. Next you use
the various set* methods to set up the observing (sources,
spectral windows, etc.). Each such setup should be given a
unique name that will be used in the next step. Then you call the observe method for each observing scan you wish to make. Here you
specify the source name, spectral windoow name, and observing
times. After this, you have a MeasurementSet that is complete but
empty. In the next phase, you fill the MeasurementSet with data from a
model and then corrupt the measurements (if desired). To fill it in
with a model, use the predict method. Finally, to apply errors, first
set up the various effects using the relevant set* methods, and
then call corrupt.
Some important points (mostly for the cognoscenti):
- One call to observe generates one scan (all rows have
the same SCAN_NUMBER).
- The start and stop times specified to observe need not be
contiguous and so one can simulate antenna drive times.
- Currently there is no facility for patterns of observing, such
as mosaicing, since it is easy to do this via sequences of calls of
observe.
- The heavy duty columns (DATA, FLAG, IMAGING_WEIGHT, etc.
are tiled. New tiles are generated for each scan. Thus the TSM files
will not get very large.
newsimulator changes some columns to the MeasurementSet to store
results of processing. The following columns in the MS are
particularly important:
- DATA
- The original observed visibilities are in a column
called DATA. These are normally not altered by any processing in
AIPS++. However, this simulation program does overwrite these
values.
- CORRECTED_DATA
- During a calibration process, as carried out by
e.g. calibrater, the visibilities may be
corrected for calibration effects. This corrected visibilities are
stored in a column CORRECTED_DATA which is created on demand.
- MODEL_DATA
- During various phases of processing, the
visibilities as predicted from some model are required. These
model visibilities are stored in a column MODEL_DATA. The
ft function of the imager
tool should be used to calculate the model visibility for a
model image or componentmodels.
Standard tools such as the table module and the
ms can be used to access and possibly change these (and
all other) columns.
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