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Field Center Coordinates
This panel is visible if Individual Pointing(s) has been selected in the Source panel. The number of pointings that can be defined is nominally 150 per Science Goal, distributed between multiple sources. In practice, more pointings can be created if the source list can be split into multiple clusters. It is possible to define multiple pointings per source, but each one must overlap such that they form a single mosaic. If multiple mosaics are required, they must be placed in separate Field Sources.
- Coords Type: Field centre in relative or absolute coordinates. Relative positions are offset from the source coordinate and are recommended. Absolute coordinates can be entered, but will be converted to offsets from the source coordinate during SB generation as absolute coordinates cannot be used with the telescope control system.
- Offset Unit: If relative coordinates have been selected, set the unit of the offset (usually arcsec).
- #Pointings: A count of how many pointings have been defined, useful when there are many.
- RA and Dec: The position of each pointing should be entered in this table, usually relative to the source coordinate. Absolute coordinates are also possible, but are not recommended.
At the bottom of the panel are buttons which allow a user to add and delete pointings manually, but also to import and export them from and to an external ASCII file. The file format is very flexible and allows a user to write out the pointing positions in either offset or absolute coordinates and will automatically do the conversion between the two i.e. one can export in a different system to what is displayed. An example of the format for absolute coordinates in sexagesimal is shown here:
RA , Dec, Coordinate Type, Coordinate Units
-- This signals end of the header
04:31:38.4369, 18:13:57.651,Absolute,Sexagesimal
04:31:40.5426, 18:13:57.650,Absolute,Sexagesimal
04:31:36.3312, 18:13:57.650,Absolute,Sexagesimal
The ``Absolute'' coordinate type can be combined with the units ``Sexagesimal'', ``Degrees'' or ``Radians'', whilst ``Offset'' pointings can be defined in ``Arcsecs'', ``Arcmin'' or ``Degrees''. Both the unit and coordinate type are case-insensitive. Galactic coordinates are not supported.
Next: Rectangle
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The ALMA OT Team, 2018 Sep 25