FIELD Field position for each source.

Name

Format

Units

Measure

Comments

Columns

Data

FIELD_NAME

String Name of field

CODE

String Special characteristics of field

TIME

Double s EPOCH Time origin for directions and rates

NUM_POLY

Int Series order Npoly

DELAY_DIR

Double(2, Npoly+1) rad DIRECTION Direction of delay center

PHASE_DIR

Double(2, Npoly+1) rad DIRECTION Phase center

REFERENCE_DIR

Double(2, Npoly+1) rad DIRECTION Reference center

SOURCE_ID

Int Source identifier

EPHEMERIS_ID

Int Ephemeris identifier

ASSOC_FIELD_ID

Int(*) Associate field identifier

ASSOC_NATURE

String Nature of the association

Flags

FLAG_ROW

Bool The row flag
Notes: The FIELD table defines a field position on the sky. For interferometers, this is the correlated field position. For single dishes, this is the nominal pointing direction.
FIELD_NAME
Field name; user specified.  
CODE
Field code indicating special characteristics of the field; user specified. The notion of pattern contained in the concept of OBSERVATION (ALMA glossary) is associated here to the polynomial forms which describe an elementary pattern. OBS_INTENT  belongs to the STATE sub-table. ALMA can use here this CODE as needed.   
TIME
Time reference for the directions and rates. Require to use the same TIME Measure reference as in the MAIN.
NUM_POLY
Series order for the *_DIR columns.
DELAY_DIR
Direction of delay center; can be expressed as a polynomial in time. Final result converted to the defined Direction Measure type.
PHASE_DIR
Direction of the phase center; can be expressed as a polynomial in time. Final result converted to the defined Direction Measure type.
REFERENCE_DIR
Reference center; can be expressed as a polynomial in time. Final result converted to the defined Direction Measure type. Used in single-dish to record the associated reference direction if position switching has already been applied. For interferometric data, this is the original correlated field center, and may equal the DELAY_DIR or PHASE_DIR.
SOURCE_ID
Points to an entry in the SOURCE sub-table; a value of -1 indicates there is no corresponding source defined (as this will be the case for the radiometric data) 
EPHEMERIS_ID
Points to an entry to the EPHEMERIS sub-table, which defines the ephemeris used to compute the field position. Useful for moving, near-field objects, where the ephemeris may be revised over time.
ASSOC_FIELD_ID
Associated field identifier(s) for fields(s) which are related in some fashion (e.g. field of the phase reference source when using fast switching mode) 
ASSOC_NATURE
Nature of the association e.g. phase reference source 
FLAG_ROW
True if in this row are invalid, else False. Does not imply flagging in MAIN