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The siarray argument for isigopen
, osigopen
,
wfdbinit
, and osigfopen
is a pointer to an array of
objects of type WFDB_Siginfo
. The first three of these functions
fill in the WFDB_Siginfo
objects to which siarray points, but
the caller must supply initialized WFDB_Siginfo
objects to
osigfopen
. Each object specifies the attributes of a
signal:
char *fname
fname
with each of the components of the
database path in turn (see section 1.4 The Database Path and Other Environment Variables). fname
may include
relative or absolute path specifications if necessary; the use of an
absolute pathname, combined with an initial null component in WFDB
,
reduces the time needed to find the signal file to a minimum. If
fname
is `-', it refers to the standard input or
output.
char *desc
desc
string is restricted to a maximum of WFDB_MAXDSL
(defined in `<wfdb/wfdb.h>') characters, not including the null.
char *units
units
string is
restricted to a maximum of WFDB_MAXUSL
(defined in
`<wfdb/wfdb.h>') characters (not including the null).
WFDB_Gain gain
gain
is zero, no amplitude calibration is available; in this
case, a gain
of WFDB_DEFGAIN
(defined in
`<wfdb/wfdb.h>') may be assumed.
WFDB_Sample initval
WFDB_Group group
WFDB_Siginfo
structures are always kept ordered with respect
to the group number, so that signals belonging to the same group are
described by consecutive entries in siarray.
int fmt
int spf
spf
may be any
positive integer. Note that non-integer values are not permitted (thus
the frame rate must be chosen such that all sampling frequencies used in
the record are integer multiples of the frame rate).
int bsize
bsize
field
indicates how many bytes must be read or written at a time
(see section 5.7 Signals That Are Not Stored in Disk Files). For ordinary disk files, bsize
is zero.
All signals belonging to a given group have the same
bsize
.
int adcres
int adczero
adczero
is usually zero. For the MIT DB,
however, an offset binary ADC was used, and adczero
was 1024.
int baseline
adczero
is not synonymous with that of
baseline
(the isoelectric or physical zero level of the signal); the
baseline
is a characteristic of the signal, while
adczero
is a characteristic of the digitizer. The value
of baseline
need not necessarily lie within the output range of
the ADC; for example, if the units
are `degrees_Kelvin',
and the ADC range is 200--300 degrees Kelvin, baseline
corresponds to
absolute zero, and lies well outside the range of values actually produced
by the ADC.
long nsamp
nsamp
is the number of samples divided by spf
, see above, i.e.,
the number of frames.) All signals in a given record must have the same
nsamp
. If nsamp
is zero, the number of samples is unspecified,
and the cksum
(see the next item) is not used; this is useful for
specifying signals that are obtained from pipes, for which the length may not
be known.
int cksum
newheader
records checksums calculated by
putvec
when it creates a new `hea' file, and
getvec
compares checksums that it calculates against cksum
at the end of the record, provided that the entire record was read
through without skipping samples.
The number of WFDB_Siginfo
structures in siarray is given by
the nsig argument of the functions that open signal files. Input
and output signal numbers are assigned beginning with 0 in the order in
which the signals are given in siarray. Note that input signal 0
and output signal 0 are distinct. Input signal numbers are supplied to
aduphys
, physadu
, adumuv
, and muvadu
in
their first arguments. See section Example 5: Reading Signal Specifications, for an illustration of how to
read signal specifications from WFDB_Siginfo
structures.
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