This
application computes and displays simple statistics for the pixels in an
NDF’s data,
quality or variance array. The statistics available are:
-
the pixel sum,
-
the pixel mean,
-
the pixel population standard deviation,
-
the pixel population skewness and excess kurtosis,
-
the value and position of the minimum- and maximum-valued pixels,
-
the total number of pixels in the NDF,
-
the number of pixels used in the statistics, and
-
the number of pixels omitted.
Iterative -sigma
clipping may also be applied as an option (see Parameter CLIP).
Order statistics (median and percentiles) may optionally be derived and displayed (see
Parameters ORDER and PERCENTILES). Although this can be a relatively slow operation on
large arrays, unlike HISTAT the reported order statistics are accurate, not
approximations, irrespective of the distribution of values being analysed.
CLIP( ) = _REAL (Read)
An optional
one-dimensional array of clipping levels to be applied, expressed as standard
deviations. If a null value is supplied for this parameter (the default), then no
iterative clipping will take place and the statistics computed will include all the
valid NDF pixels.
If an array of clipping levels is given, then the routine will first compute statistics using
all the available pixels. It will then reject all those pixels whose values lie outside
standard deviations
of the mean (where
is the first value supplied) and will then re-evaluate the statistics. This rejection
iteration is repeated in turn for each value in the CLIP array. A maximum of five
values may be supplied, all of which must be positive. [!]
The name of the NDF array component for which statistics are required: "Data", "Error",
"Quality" or "Variance" (where "Error" is the alternative to "Variance" and causes the
square root of the variance values to be taken before computing the statistics).
If "Quality" is specified, then the quality values are treated as numerical
values (in the range 0 to 255). ["Data"]
LOGFILE = FILENAME (Write)
A text
file into which the results should be logged. If a null value is supplied (the
default), then no logging of results will take place. [!]
NDF = NDF (Read)
The NDF data structure to be analysed.
ORDER = _LOGICAL (Read)
Whether
or not to calculate order statistics. If set TRUE the median and optionally
percentiles are determined and reported. [FALSE]
PERCENTILES( 100 ) = _REAL (Read)
A list of percentiles to be found. None are computed if this parameter is
null (!). The percentiles must be in the range 0.0 to 100.0. This parameter is
ignored unless ORDER is TRUE. [!]
KURTOSIS = _DOUBLE
(Write)
The population excess kurtosis of all the valid pixels in the NDF
array. This is the normal kurtosis minus 3, such that a Gaussian distribution
of values would generate an excess kurtosis of 0.
MAXCOORD( ) = _DOUBLE
(Write)
A one-dimensional array of values giving the
WCS co-ordinates of the
centre of the (first) maximum-valued pixel found in the NDF array. The number of
co-ordinates is equal to the number of NDF dimensions.
MAXIMUM = _DOUBLE
(Write)
The maximum pixel value found in the NDF array.
MAXPOS( ) = _INTEGER
(Write)
A one-dimensional array of
pixel indices identifying the (first)
maximum-valued pixel found in the NDF array. The number of indices is equal to
the number of NDF dimensions.
MAXWCS = LITERAL (Write)
The formatted WCS
co-ordinates at the maximum pixel value. The individual axis values are comma
separated.
MEAN = _DOUBLE (Write)
The mean value of all the valid pixels
in the NDF array.
MEDIAN = _DOUBLE (Write)
The median value of all the
valid pixels in the NDF array when ORDER is TRUE.
MINCOORD( ) = _DOUBLE
(Write)
A one-dimensional array of values giving the data co-ordinates of the
centre of the (first) minimum-valued pixel found in the NDF array. The number of
co-ordinates is equal to the number of NDF dimensions.
MINIMUM = _DOUBLE
(Write)
The minimum pixel value found in the NDF array.
MINPOS( ) = _INTEGER
(Write)
A one-dimensional array of pixel indices identifying the (first)
minimum-valued pixel found in the NDF array. The number of indices is equal
to the number of NDF dimensions.
MINWCS = LITERAL (Write)
The formatted
WCS co-ordinates at the minimum pixel value. The individual axis values are
comma separated.
NUMBAD = _INTEGER (Write)
The number of pixels which
were either not valid or were rejected from the statistics during iterative
-sigma
clipping.
NUMGOOD = _INTEGER (Write)
The number of NDF pixels which actually
contributed to the computed statistics.
NUMPIX = _INTEGER (Write)
The total number
of pixels in the NDF (both good and bad).
PERVAL() = _DOUBLE (Write)
The values of
the percentiles of the good pixels in the NDF array. This parameter is only
written when one or more percentiles have been requested.
SIGMA = _DOUBLE
(Write)
The population standard deviation of the pixel values in the NDF
array.
SKEWNESS = _DOUBLE (Write)
The population skewness of all the valid
pixels in the NDF array.
TOTAL = _DOUBLE (Write)
The sum of the pixel
values in the NDF array.