Table 1: FIELD: Field position for each source
FIELD: Field positions of each source

Name

Format

Units

Measure

Comments

Columns

Data

NAME

String

s

Name of field.

CODE

String

s

Special characteristics of field.

TIME

Double

s

EPOCH

Time origin for directions and rates.

NUM_POLY

Int

Series order.

DELAY_DIR

Double(2,
NUM_POLY+1)

rad

DIRECTION

Direction of delay center

PHASE_DIR

Double(2,
NUM_POLY+1)

rad

DIRECTION

Phase center

REFERENCE_DIR

Double(2,
NUM_POLY+1)

rad

DIRECTION

Reference center

( SOURCE_ID)

Int

Index in source table.

( EPHEMERIS_ID)

Int

Ephemeris id

( FIELD_ID)   

Int(*)

Associated field identifier(s)

(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.
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 smae 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 cente; 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.
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