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ccdstat - statistics (1st through 4th moment) and chi2
ccdstat
in=image [parameter=value]
ccdstat calculates all moments (up
to fourth order) of the values in an image/cube, and calculate some human
understandable numbers (mean, dispersion, skewness, curtosis) from them.
It can optionally use a weighting map, in case the map needs to be weighted
per pixel.
Optionally, if the map contains an error normalized difference
between an observation and model, it can also compute a chi2 goodness of
fit if the number of of fitting parameters is given (npar, must be > 0
to trigger this option), as well as the number of independant points per
beam (nppb):
chi2 = sum_{i,j}(map(i,j)^2)/nppb/(N/nppb-npar)
where N is the number of non-bad values in the map. The input map is now
assumed to contain a dimensionless (obs-mod)/sigma
The following
parameters are recognized in order; they may be given in any order if the
keyword is also given. Use --help to confirm this man page is up to date.
- in=in-file
- input file, in Image(5)
format [no default]
- min=min_value
- If
given, all values below this value are ignored in the statistics. By default
no lower limit is used.
- max=max_value
- If given, all values above this value
are ignored in the statistics. By default no upper limit is used.
- bad=bad_value
- If given, all values identical to this value are ignored in the statistics.
Note that, apart for bad=0, it is dangerous to use equating to a real value
as a masking operating.
- win=weight-file
- optional input file, in Image(5)
format, of which the mapvalues are used as a relative weight factor. Should
be all positive, with 0 meaning no weight. [no default]
- npar=
- Number of
fitting parameters. If given > 0, this will trigger the computation of chi2
goodness of fit, instead of the normal statistics.
- nppb=
- Number of (independant)
points per beam. Only used in the computation for chi2, and
- median=t|f
- Optional
display of the median value
- torben=t|f
- Use the torben method to compute
the median. [Default: f]
- robust=t|f
- Conmpute robust mean, median and dispersion.
[Default: f]
- mmcount=t|f
- Count occurances of min and max
- maxpos=t|f
- Report
the location where the max occured. [Default: f]
- half=f|t
- Only use half (negative)
values and symmetrize them
- maxmom=
- Maximum moments it should compute. The
current maximum is 4, moments up through the kurtosis are computed. For
maxmom<0 no work is done, except for reading the file, which can be used
to benchmark your disk I/O for large NEMO images. [Default: 4].
- ignore=t|f
- This will ignore the cell width when summing emission for any axis that
has only one cell (assumed infinity, or a result of ccdmom(1NEMO)
). Setting
this to false, will not ignore that cell width. [Default : t]
- sort=t|f
- Sorting
routine (not activated yet) Flux not implemented yet. [ Default: f]
- planes=-1|0|start:end:step
- Either the whole cube is taken as one (-1, the default), or planes can be
selected. 0 means all planes, if a start:end:step is selected, only those
planes are. Step defaults to 1. Default: -1
- tab=
- If a table output filename
is given, data values are written here. otherwise on screen.
- qac=t|f
- If selected,
a QAC listing is selected. This gives the mean, rms, min and max. [Default:
f]
% ccdstat image.ccd min=-2
Min=-1.879409 Max=2.265516
Number of points : 95
Mean and dispersion : 0.097891 0.956030
Skewness and kurtosis: -0.059936 -0.654776
5/100 out-of-range points discarded
Here is an example how to created a weight file which is a circular annulus:
% ccdmath out=map1 "fie=iflt(%r,50,1,0)" size=200,200 crpix=100,100
% ccdmath out=map2 "fie=iflt(%r,20,1,0)" size=200,200 crpix=100,100
% ccdmath map1,map2 map3 %1-%2
Here is an two masking example: firstignoring the exact value of 0, followed
by an example of a small range around 0:
% ccdstat map1 bad=0
% ccdmath map1 - ’iflt(abs(%1),0.001,0,%1)’ | ccdstat - bad=0
Here is an example of calculating the chi2 goodness of fit for a gaussian
distribution:
% ccdmath "" - "rang(0,1)" | ccdstat - npar=1
Generating a map from scratch
chi2= 1.03431
df= 98
snapccd(1NEMO)
, image(5NEMO)
Peter Teuben
src/image/misc ccdstat.c
4-Oct-88 V1.0: Created PJT
9-may-03 V1.3: added bad= PJT
5-jun-03 V1.4: added win= PJT
14-nov-04 V1.5: added the chi2 trigger with npar= and nppb= PJT
24-may-06 V1.8: added mmcount PJT
15-oct-11 V1.10: added maxmom= and bench options PJT
14-feb-13 V2.0: ignore=t to properly handle units PJT
4-dec-2020 V3.8: added qac= PJT
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