Mark5BHeader

class baseband.mark5b.Mark5BHeader(words, kday=None, ref_time=None, verify=True)[source] [edit on github]

Bases: baseband.base.header.VLBIHeaderBase

Decoder/encoder of a Mark5B Frame Header.

See page 15 of https://www.haystack.mit.edu/tech/vlbi/mark5/docs/Mark%205B%20users%20manual.pdf

Parameters
wordstuple of int, or None

Four 32-bit unsigned int header words. If None, set to a tuple of zeros for later initialisation.

kdayint 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_timeTime or None

Reference time within 500 days of the observation time, used to infer the full MJD. Used only if kday is not given.

verifybool, optional

Whether to do basic verification of integrity. Default: True.

Returns
headerMark5BHeader

Attributes Summary

complex_data

Whether the data are complex (always False for Mark5B).

fraction

Fractional seconds (decoded from 'bcd_fraction').

frame_nbytes

Size of the frame in bytes (always 10016 for Mark5B).

jday

Last three digits of MJD (decoded from 'bcd_jday').

kday

Thousands of MJD, to complement jday from header.

mutable

Whether the header can be modified.

nbytes

Size of the header in bytes.

payload_nbytes

Size of the payload in bytes (always 10000 for Mark5B).

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(*[, verify])

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.

invariant_pattern([invariants])

Pattern and mask shared between headers of a type or stream.

invariants()

Set of keys of invariant header parts.

keys()

All keys defined for this header.

set_time(time[, frame_rate])

Convert Time object to BCD timestamp elements and 'frame_nr'.

tofile(fh)

Write VLBI frame header to filehandle.

update(*[, time, frame_rate, crc, verify])

Update the header by setting keywords or properties.

verify()

Verify header integrity.

Attributes Documentation

complex_data

Whether the data are complex (always False for Mark5B).

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.

frame_nbytes

Size of the frame in bytes (always 10016 for Mark5B).

jday

Last three digits of MJD (decoded from ‘bcd_jday’).

kday = None

Thousands of MJD, to complement jday from header.

mutable

Whether the header can be modified.

nbytes

Size of the header in bytes.

payload_nbytes

Size of the payload in bytes (always 10000 for Mark5B).

seconds

Integer seconds on day (decoded from ‘bcd_seconds’).

time

Convert year, BCD time code to Time object.

Calculate time using jday, seconds, and fraction properties (which reflect the bcd-encoded ‘bcd_jday’, ‘bcd_seconds’ and ‘bcd_fraction’ header items), plus kday from the initialisation. See https://www.haystack.mit.edu/tech/vlbi/mark5/docs/Mark%205B%20users%20manual.pdf

Note 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_rateQuantity, optional

Used to calculate the fractional second from the frame number instead of from the header’s fraction.

Returns
Time

Methods Documentation

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.

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.

classmethod fromkeys(*args, **kwargs) [edit on github]

Initialise a header from parsed values.

Like fromvalues, but without any interpretation of keywords.

Raises
KeyErrorif not all keys required are present in kwargs
classmethod fromvalues(*, verify=True, **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 as jday and seconds.

Given defaults:

sync_pattern : 0xABADDEED

Values set by other keyword arguments (if present):

bcd_jday : from jday or time bcd_seconds : from seconds or time bcd_fraction : from fraction or time (may need frame_rate) frame_nr : from time (may need frame_rate)

get_time(frame_rate=None)[source] [edit on github]

Convert year, BCD time code to Time object.

Calculate time using jday, seconds, and fraction properties (which reflect the bcd-encoded ‘bcd_jday’, ‘bcd_seconds’ and ‘bcd_fraction’ header items), plus kday from the initialisation. See https://www.haystack.mit.edu/tech/vlbi/mark5/docs/Mark%205B%20users%20manual.pdf

Note 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_rateQuantity, optional

Used to calculate the fractional second from the frame number instead of from the header’s fraction.

Returns
Time
infer_kday(ref_time)[source] [edit on github]

Uses a reference time to set a header’s kday.

Parameters
ref_timeTime

Reference time within 500 days of the observation time.

classmethod invariant_pattern(invariants=None, **kwargs) [edit on github]

Pattern and mask shared between headers of a type or stream.

This is mostly for use inside locate_frames().

Parameters
invariantsset of str, optional

Set of keys to header parts that are shared between all headers of a given type or within a given stream/file. Default: from invariants().

**kwargs

Keyword arguments needed to instantiate an empty header. (Mostly for Mark 4).

Returns
patternlist of int

The pattern that is shared between headers. If called on an instance, just the header words; if called on a class, words with defaults for the relevant parts set.

masklist of int

For each entry in pattern a bit mask with bits set for the parts that are invariant.

classmethod invariants() [edit on github]

Set of keys of invariant header parts.

On the class, this returns keys of parts that are shared by all headers for the type, on an instance, those that are shared with other headers in the same file.

If neither are defined, returns ‘sync_pattern’ if the header containts that key.

keys() [edit on github]

All keys defined for this header.

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
timeTime

The time to use for this header.

frame_rateQuantity, optional

For calculating ‘frame_nr’ from the fractional seconds.

tofile(fh) [edit on github]

Write VLBI frame header to filehandle.

update(*, time=None, frame_rate=None, crc=None, verify=True, **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
timeTime, optional

A possible new time. This is updated last.

frame_rateQuantity, optional

The frame rate to use in calculating the frame number from the time. Needed for times at non-integer seconds.

crcint or None, optional

If None (default), recalculate the CRC after updating.

verifybool, optional

If True (default), verify integrity after updating.

**kwargs

Arguments used to set keywords and properties.

verify()[source] [edit on github]

Verify header integrity.