MAKETIME (Jul98) ftools.time MAKETIME (Jul98)
NAME
maketime -- Create Good Time Interval (GTI) FITS file based on
parameters in a Housekeeping data FITS file.
USAGE
maketime infile outfile expr name value time compact
DESCRIPTION
This task creates a GTI table from a subset of times in an
input HK table. The rows are selected on the basis of a boolean
expression whose variables are either parameters in the NAME column
(for compact format HK files) or column names (for expanded format
HK files). If, after substituting the values associated with a
particular parameter into the variables, the expression evaluates
to true, then the time is included in the GTI table.
General Expression Syntax
The expression can be an arbitrarily complex series of operations
performed on constants, keyword values, and column data taken from
the specified FITS TABLE extension.
Keyword and column data are referenced by name. Any string of
characters not surrounded by quotes (ie, a constant string) or
followed by an open parentheses (ie, a function name) will be
initially interpretted as a column name and its contents for the
current row inserted into the expression. If no such column
exists, a keyword of that name will be searched for and its value
used, if found. To force the name to be interpretted as a keyword
(in case there is both a column and keyword with the same name),
precede the keyword name with a single pound sign, '#', as in
'#NAXIS2'. Due to the generalities of FITS column and keyword
names, if the column or keyword name contains a space or a
character which might appear as an arithmetic term then inclose the
name in '$' characters as in $MAX PHA$ or #$MAX-PHA$. Names are
case insensitive.
To access a table entry in a row other than the current one, follow
the column's name with a row offset within curly braces. For
example, 'PHA{-3}' will evaluate to the value of column PHA, 3 rows
above the row currently being processed. One cannot specify an
absolute row number, only a relative offset. Rows that fall outside
the table will be treated as undefined, or NULLs.
Boolean operators can be used in the expression in either their
Fortran or C forms. The following boolean operators are available:
"equal" .eq. .EQ. == "not equal" .ne. .NE. !=
"less than" .lt. .LT. < "less than/equal" .le. .LE. <= =<
"greater than" .gt. .GT. > "greater than/equal" .ge. .GE. >= =>
"or" .or. .OR. || "and" .and. .AND. &&
"negation" .not. .NOT. ! "approx. equal(1e-7)" ~
Note that the exclamation point, '!', is a special UNIX character,
so if it is used on the command line rather than entered at a task
prompt, it must be preceded by a backslash to force the UNIX shell
to ignore it.
The expression may also include arithmetic operators and functions.
Trigonometric functions use radians, not degrees. The following
arithmetic operators and functions can be used in the expression
(function names are case insensitive). A null value will be
returned in case of illegal operations such as divide by zero,
sqrt(negative) log(negative), log10(negative), arccos(.gt. 1),
arcsin(.gt. 1).
"addition" + "subtraction" -
"multiplication" * "division" /
"negation" - "exponentiation" ** ^
"absolute value" abs(x) "cosine" cos(x)
"sine" sin(x) "tangent" tan(x)
"arc cosine" arccos(x) "arc sine" arcsin(x)
"arc tangent" arctan(x) "arc tangent" arctan2(x,y)
"hyperbolic cos" cosh(x) "hyperbolic sin" sinh(x)
"hyperbolic tan" tanh(x) "round to nearest int" round(x)
"round down to int" floor(x) "round up to int" ceil(x)
"exponential" exp(x) "square root" sqrt(x)
"natural log" log(x) "common log" log10(x)
"modulus" i % j "random # [0.0,1.0)" random()
"minimum" min(x,y) "maximum" max(x,y)
"if-then-else" b?x:y
An alternate syntax for the min and max functions has only a single
argument which should be a vector value (see below). The result
will be the minimum/maximum element contained within the vector.
In the if-then-else expression, "b?x:y", b is an explicit boolean
value or expression. There is not automatic type conversion from
numeric to boolean values, so one needs to use "iVal!=0" instead of
merely "iVal" as the boolean argument. x and y can be any scalar
data type (including string).
The following type casting operators are available, where the
inclosing parentheses are required and taken from the C language
usage. Also, the integer to real casts values to double precision:
"real to integer" (int) x (INT) x
"integer to real" (float) i (FLOAT) i
In addition, several constants are built in for use in numerical
expressions:
#pi 3.1415... #e 2.7182...
#deg #pi/180 #row current row number
#null undefined value #snull undefined string
A string constant must be enclosed in quotes as in 'Crab'. The
"null" constants are useful for conditionally setting table values
to a NULL, or undefined, value (eg., "col1==-99 ? #NULL : col1").
There is also a function for testing if two values are close to each
other, i.e., if they are "near" each other to within a user
specified tolerance. The arguments, value_1 and value_2 can be
integer or real and represent the two values who's proximity is
being tested to be within the specified tolerance, also an integer
or real:
near(value_1, value_2, tolerance)
When a NULL, or undefined (INDEF), value is encountered in the FITS
table, the expression will evaluate to NULL unless the undefined
value is not actually required for evaluation, eg. "TRUE .or.
NULL" evaluates to TRUE. The following two functions allow some
NULL detection and handling:
"a null value?" ISNULL(x)
"define a value for null" DEFNULL(x,y)
The former returns a boolean value of TRUE if the argument x is
NULL. The later "defines" a value to be substituted for NULL
values; it returns the value of x if x is not NULL, otherwise it
returns the value of y.
Bit Masks
Bit masks can be used to select out rows from bit columns (TFORMn =
#X) in FITS files. To represent the mask, binary, octal, and hex
formats are allowed:
binary: b0110xx1010000101xxxx0001
octal: o720x1 -> (b111010000xxx001)
hex: h0FxD -> (b00001111xxxx1101)
In all the representations, an x or X is allowed in the mask as a
wild card. Note that the x represents a different number of wild
card bits in each representation. All representations are case
insensitive.
To construct the boolean expression using the mask as the boolean
equal operator discribed above on a bit table column. For example,
if you had a 7 bit column named flags in a FITS table and wanted
all rows having the bit pattern 0010011, the selection expression
would be:
flags == b0010011
or
flags .eq. b10011
It is also possible to test if a range of bits is less than, less
than equal, greater than and greater than equal to a particular
boolean value:
flags <= bxxx010xx
flags .gt. bxxx100xx
flags .le. b1xxxxxxx
Notice the use of the x bit value to limit the range of bits being
compared.
It is not necessary to specify the leading (most significant) zero
(0) bits in the mask, as shown in the second expression above.
Bit wise AND, OR and NOT operations are also possible on two or more
bit fields using the '&'(AND), '|'(OR), and the '!'(NOT) operators.
All of these operators result in a bit field which can then be used
with the equal operator. For example:
(!flags) == b1101100
(flags & b1000001) == bx000001
Bit fields can be appended as well using the '+' operator. Strings
can be concatenated this way, too.
Vector Columns
Vector columns can also be used in building the expression. No
special syntax is required if one wants to operate on all elements
of the vector. Simply use the column name as for a scalar column.
Vector columns can be freely intermixed with scalar columns or
constants in virtually all expressions. The result will be of the
same dimension as the vector. Two vectors in an expression, though,
need to have the same number of elements and have the same
dimensions. The only places a vector column cannot be used (for
now, anyway) are the SAO region functions and the NEAR boolean
function.
Arithmetic and logical operations are all performed on an element by
element basis. Comparing two vector columns, eg "COL1 == COL2",
thus results in another vector of boolean values indicating which
elements of the two vectors are equal.
Eight functions are available that operate on a vector and return a
scalar result:
"minimum" MIN(V) "maximum" MAX(V)
"average" AVERAGE(V) "median" MEDIAN(V)
"sumation" SUM(V) "standard deviation" STDDEV(V)
"# of values" NELEM(V) "# of non-null values" NVALID(V)
where V represents the name of a vector column or a manually
constructed vector using curly brackets as described below. The
first 6 of these functions ignore any null values in the vector when
computing the result.
The SUM function literally sums all the elements in x, returning
a scalar value. If V is a boolean vector, SUM returns the
number of TRUE elements. The NELEM function returns the number of
elements in vector V whereas NVALID return the number of non-null
elements in the vector. (NELEM also operates on bit and
string columns, returning their column widths.) As an example,
to test whether all elements of two vectors satisfy a given
logical comparison, one can use the expression
SUM( COL1 > COL2 ) == NELEM( COL1 )
which will return TRUE if all elements of COL1 are greater than
their corresponding elements in COL2.
To specify a single element of a vector, give the column name
followed by a comma-separated list of coordinates enclosed in
square brackets. For example, if a vector column named PHAS exists
in the table as a one dimensional, 256 component list of numbers
from which you wanted to select the 57th component for use in the
expression, then PHAS[57] would do the trick. Higher dimensional
arrays of data may appear in a column. But in order to interpret
them, the TDIMn keyword must appear in the header. Assuming that a
(4,4,4,4) array is packed into each row of a column named ARRAY4D,
the (1,2,3,4) component element of each row is accessed by
ARRAY4D[1,2,3,4]. Arrays up to dimension 5 are currently
supported. Each vector index can itself be an expression, although
it must evaluate to an integer value within the bounds of the
vector. Vector columns which contain spaces or arithmetic operators
must have their names enclosed in "$" characters as with
$ARRAY-4D$[1,2,3,4].
A more C-like syntax for specifying vector indices is also
available. The element used in the preceding example alternatively
could be specified with the syntax ARRAY4D[4][3][2][1]. Note the
reverse order of indices (as in C), as well as the fact that the
values are still ones-based (as in Fortran -- adopted to avoid
ambiguity for 1D vectors). With this syntax, one does not need to
specify all of the indices. To extract a 3D slice of this 4D
array, use ARRAY4D[4].
Variable-length vector columns are not supported.
Vectors can be manually constructed within the expression using a
comma-separated list of elements surrounded by curly braces ('{}').
For example, '{1,3,6,1}' is a 4-element vector containing the values
1, 3, 6, and 1. The vector can contain only boolean, integer, and
real values (or expressions). The elements will be promoted to the
highest datatype present. Any elements which are themselves
vectors, will be expanded out with each of its elements becoming an
element in the constructed vector.
See the 'calc_express' help file for more details on the expression
syntax.
PARAMETERS
infile [filename]
A file name and extension number in square brackets of the
input HK file.
outfile [filename]
The name of the created GTI FITS file
expr [string]
The boolean expression used to calculate time intervals from
the HK file. You may use the "@filename" construction to load
a complex expression from a file. The file may contain
multiple lines (which are concatenated together).
name = "NAME" [string]
The column name containing the housekeeping parameter names.
This parameter is ignored for expanded (compact=no) files.
value = "VALUE" [string]
The column name containing the housekeeping parameter values.
This parameter is ignored for expanded (compact=no) files.
time = "TIME" [string]
The column name containing the housekeeping parameter time
stamp.
(start = "START") [string]
The output GTI column name containing the start times.
(stop = "STOP") [string]
The output GTI column name containing the stop times.
compact = yes [boolean]
The flag for compact ASCA Housekeeping FITS files. Compact
files have three columns: time, housekeeping parameter name,
and parameter value. Each row in the file indicates that the
specified parameter changed value at that time. Expanded
housekeeping files have a column for time, and a column for
each housekeeping parameter, containing the value of that
parameter at each time.
(histkw=yes) [boolean]
If true, history records will be added to the output file
primary header indicating that FMERGE created the file, and
history records of each input file will be added to the
extension header.
(prefr=0.5) [double]
This is the amount of the previous time interval to be included
in the GTI. A value of 1.0 means to include the whole
interval. If the input file has the PREFR keyword set, that
value will be used. Otherwise, the default is to take half of
the time interval as if the state change occurred between
measurements. The user may override either of these choices by
entering a value for prefr on the command line. Note that the
default value in the parameter file is -1 (to allow the code to
know whether or not it needs to reset the value) but that the
only allowed values are between 0 and 1.
(postfr=0.5) [double]
This is the amount of the following time interval to be
included in the GTI. A value of 1.0 means to include the whole
interval. If the input file has the POSTFR keyword set, that
value will be used. Otherwise, the default is to take half of
the time interval as if the state change occurred between
measurements. The user may override either of these choices by
entering a value for postfr on the command line. Note that the
default value in the parameter file is -1 (to allow the code to
know whether or not it needs to reset the value) but that the
only allowed values are between 0 and 1.
EXAMPLES
1. Generate the GTI FITS file gti.fit using the ASCA compact HK
FITS file hk.fit which has the parameter HVL3_MON equal to
either 26 or 27:
ft> maketime hk.fit gti.fit "(HVL3_MON == 26).or.(HVL3_MON == 26)" NAME VALUE TIME yes
2. Generate the GTI FITS file gti.fit using the expanded HK FITS
file hk.fit which has the parameter HVL3_MON greater than 10
and the parameter HVH3_MON less than 100:
ft> maketime hk.fit gti.fit "(HVL3_MON .gt. 10).and.(HVH3_MON < 100)" anything anything TIME no
BUGS
SEE ALSO
mgtime, fltime, hkexpand, hkunexpand, fselect, fcalc, calc_express