Data Object: visibilities

The visibility table container is used to store the raw correlator visibilities. On disk the data elements of this object are stored as std::complex<float> and the underlying container type is: visibility_store_type. However before use this object is promoted to a visibility_type, which contains std::complex<double> elements for in-memory processing.

General Information

  • Class: visibility_store_type or visibility_type

  • Class UUID: a5c26065821b6dc92b06f780f8641d0e

  • Rank: 4

  • Shape: the length of each dimension (e.g. [4, 32, 30, 128] )

  • Strides: the stride between data in each dimension (e.g. [122880, 3840, 128, 1] )

  • Total Size: the total number of data elements in the array (e.g. 491520 )

  • Element Type: std::complex<float> or std::complex<double>

Aliases

alias

full class name

visibility_store_type

hops::MHO_TableContainer<std::complex<float>,MHO_AxisPack<MHO_Axis<string>,MHO_Axis<double>,MHO_Axis<double>,MHO_Axis<double>>>

visibility_type

hops::MHO_TableContainer<std::complex<double>,MHO_AxisPack<MHO_Axis<string>,MHO_Axis<double>,MHO_Axis<double>,MHO_Axis<double>>>

Tags

The meta-data tags (key:value pairs) that are commonly associated with objects of this type are as follows:

key

description

example value

name

the container name

visibilities

baseline

the baseline name (using 2-char station codes)

Gs-Wf

baseline_shortname

the condensed baseline name (using 1-char mk4 station codes)

GE

reference_station

the reference station name

GGAO12M

reference_station_mk4id

the reference station 1-char mk4 ID code

G

remote_station

the remote station name

WESTFORD

remote_station_mk4id

the remote station 1-char mk4 ID code

E

correlation_date

time of correlation (in vex format)

2023y061d02h05m31s

start

the scan start time (in vex format)

2019y105d18h00m00s

stop

the scan stop time (in vex format)

2019y105d18h00m30s

origin

the source of the data

difx or mark4

difx_baseline_index

if the data was imported from DiFX, the integer baseline code

260

root_code

the mk4 style 6-char root code

3SMFW3

Axes

Axis Index

Name

Units

Type

Description/Example

0

polarization_product

N/A

MHO_Axis<string>

XX, XY, YY, RR, LL, XR, YL

1

channel

MHz

MHO_Axis<double>

lower channel edge (e.g. 3032.4)

2

time

s

MHO_Axis<double>

start of each AP (0, 1.0,…)

3

frequency

MHz

MHO_Axis<double>

the intra-channel frequency

Channel Axis (Index 1) - Detail

Each axis is capable of having additional data appended in the form of index tags, or interval tags. By default both difx2hops and mark42hops will append the channel axis with additional index tags which contain information needed to process the visibility data. The index tag entries along the channel axis include (but are not limited to) the following:

  • channel_id: the reference/remote channel id pairs (e.g. X04LX:X04LY)

  • bandwidth: float (MHz) e.g. 32.0 MHz

  • difx_frequency_index: integer (e.g. 0-31)

  • frequency_band: X

  • net_sideband: L (lower) or U (upper)

  • sky_frequency: float (MHz) e.g. 3032.4

An example of such index tag entries for the channel axis could look like:

index

sky_frequency

net_sideband

bandwidth

DIFX Index

channel_id

0

3032.4

L

32

7

X00LX:X00LX

1

3064.4

L

32

6

X01LX:X01LX

2

3096.4

L

32

5

X02LX:X02LX

…

…

…

…

…

…

31

10680.4

L

32

24

X31LX:X31LX