Mark5BHeader¶
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class
baseband.mark5b.
Mark5BHeader
(words, kday=None, ref_time=None, verify=True, **kwargs)[source] [edit on github]¶ Bases:
baseband.vlbi_base.header.VLBIHeaderBase
Decoder/encoder of a Mark5B Frame Header.
See page 15 of http://www.haystack.edu/tech/vlbi/mark5/docs/Mark%205B%20users%20manual.pdf
Parameters: words : tuple of int, or None
Four 32-bit unsigned int header words. If
None
, set to a tuple of zeros for later initialisation.kday : int or None
Explicit thousands of MJD of the observation time (needed to remove ambiguity in the Mark 5B time stamp). Can instead pass an approximate
ref_time
.ref_time :
Time
or NoneReference time within 500 days of the observation time, used to infer the full MJD. Used only if
kday
is not given.verify : bool, optional
Whether to do basic verification of integrity. Default:
True
.Returns: header :
Mark5BHeader
Attributes Summary
fraction
Fractional seconds (decoded from ‘bcd_fraction’). frame_nbytes
Size of the frame in bytes. jday
Last three digits of MJD (decoded from ‘bcd_jday’). kday
mutable
Whether the header can be modified. nbytes
Size of the header in bytes. payload_nbytes
Size of the payload in bytes. seconds
Integer seconds on day (decoded from ‘bcd_seconds’). time
Convert year, BCD time code to Time object. Methods Summary
copy
(**kwargs)Create a mutable and independent copy of the header. fromfile
(fh, *args, **kwargs)Read VLBI Header from file. fromkeys
(*args, **kwargs)Initialise a header from parsed values. fromvalues
(**kwargs)Initialise a header from parsed values. get_time
([frame_rate])Convert year, BCD time code to Time object. infer_kday
(ref_time)Uses a reference time to set a header’s kday
.keys
()set_time
(time[, frame_rate])Convert Time object to BCD timestamp elements and ‘frame_nr’. tofile
(fh)Write VLBI frame header to filehandle. update
(**kwargs)Update the header by setting keywords or properties. verify
()Verify header integrity. Attributes Documentation
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fraction
¶ Fractional seconds (decoded from ‘bcd_fraction’).
The fraction is stored to 0.1 ms accuracy. Following mark5access, this is “unrounded” to give the exact time of the start of the frame for any total bit rate below 512 Mbps. For rates above this value, it is no longer guaranteed that subsequent frames have unique rates.
Note to the above: since a Mark5B frame contains 80000 bits, the total bit rate for which times can be unique would in principle be 800 Mbps. However, standard VLBI only uses bit rates that are powers of 2 in MHz.
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frame_nbytes
¶ Size of the frame in bytes.
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jday
¶ Last three digits of MJD (decoded from ‘bcd_jday’).
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kday
= None¶
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mutable
¶ Whether the header can be modified.
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nbytes
¶ Size of the header in bytes.
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payload_nbytes
¶ Size of the payload in bytes.
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seconds
¶ Integer seconds on day (decoded from ‘bcd_seconds’).
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time
¶ Convert year, BCD time code to Time object.
Calculate time using
jday
,seconds
, andfraction
properties (which reflect the bcd-encoded ‘bcd_jday’, ‘bcd_seconds’ and ‘bcd_fraction’ header items), pluskday
from the initialisation. See http://www.haystack.edu/tech/vlbi/mark5/docs/Mark%205B%20users%20manual.pdfNote that some non-compliant files do not have ‘bcd_fraction’ set. For those, the time can still be calculated using the header’s ‘frame_nr’ by passing in a frame rate.
Furthermore, fractional seconds are stored only to 0.1 ms accuracy. In the code, this is “unrounded” to give the exact time of the start of the frame for any total bit rate below 512 Mbps. For higher rates, it is no longer guaranteed that subsequent frames have unique
fraction
, and one should pass in an explicit frame rate instead.Parameters: frame_rate :
Quantity
, optionalUsed to calculate the fractional second from the frame number instead of from the header’s
fraction
.Returns:
Methods Documentation
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copy
(**kwargs)[source] [edit on github]¶ Create a mutable and independent copy of the header.
Keyword arguments can be passed on as needed by possible subclasses.
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classmethod
fromfile
(fh, *args, **kwargs) [edit on github]¶ Read VLBI Header from file.
Arguments are the same as for class initialisation. The header constructed will be immutable.
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classmethod
fromkeys
(*args, **kwargs) [edit on github]¶ Initialise a header from parsed values.
Like fromvalues, but without any interpretation of keywords.
Raises: KeyError : if not all keys required are present in kwargs
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classmethod
fromvalues
(**kwargs)[source] [edit on github]¶ Initialise a header from parsed values.
Here, the parsed values must be given as keyword arguments, i.e., for any
header = cls(<data>)
,cls.fromvalues(**header) == header
.However, unlike for the
Mark5BHeader.fromkeys()
class method, data can also be set using arguments named after methods, such asjday
andseconds
.Given defaults:
sync_pattern : 0xABADDEED
Values set by other keyword arguments (if present):
bcd_jday : from
jday
ortime
bcd_seconds : fromseconds
ortime
bcd_fraction : fromfraction
ortime
(may needframe_rate
) frame_nr : fromtime
(may needframe_rate
)
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get_time
(frame_rate=None)[source] [edit on github]¶ Convert year, BCD time code to Time object.
Calculate time using
jday
,seconds
, andfraction
properties (which reflect the bcd-encoded ‘bcd_jday’, ‘bcd_seconds’ and ‘bcd_fraction’ header items), pluskday
from the initialisation. See http://www.haystack.edu/tech/vlbi/mark5/docs/Mark%205B%20users%20manual.pdfNote that some non-compliant files do not have ‘bcd_fraction’ set. For those, the time can still be calculated using the header’s ‘frame_nr’ by passing in a frame rate.
Furthermore, fractional seconds are stored only to 0.1 ms accuracy. In the code, this is “unrounded” to give the exact time of the start of the frame for any total bit rate below 512 Mbps. For higher rates, it is no longer guaranteed that subsequent frames have unique
fraction
, and one should pass in an explicit frame rate instead.Parameters: frame_rate :
Quantity
, optionalUsed to calculate the fractional second from the frame number instead of from the header’s
fraction
.Returns:
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infer_kday
(ref_time)[source] [edit on github]¶ Uses a reference time to set a header’s
kday
.Parameters: ref_time :
Time
Reference time within 500 days of the observation time.
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keys
() [edit on github]¶
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set_time
(time, frame_rate=None)[source] [edit on github]¶ Convert Time object to BCD timestamp elements and ‘frame_nr’.
For non-integer seconds, the frame number will be calculated if not given explicitly. Doing so requires the frame rate.
Parameters: time :
Time
The time to use for this header.
frame_rate :
Quantity
, optionalFor calculating ‘frame_nr’ from the fractional seconds.
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tofile
(fh) [edit on github]¶ Write VLBI frame header to filehandle.
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update
(**kwargs)[source] [edit on github]¶ Update the header by setting keywords or properties.
Here, any keywords matching header keys are applied first, and any remaining ones are used to set header properties, in the order set by the class (in
_properties
).Parameters: crc : int or None, optional
If
None
(default), recalculate the CRC after updating.verify : bool, optional
If
True
(default), verify integrity after updating.**kwargs
Arguments used to set keywords and properties.
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verify
()[source] [edit on github]¶ Verify header integrity.
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