DB_COCO

COMMAND TYPE : UTILITY

PURPOSE:

To perform conversion of celestial coordinates from one system to another.

DESCRIPTION:

With this command you can transform the coordinates of a catalogue and produce an output file that can be inserted in your Personal Data Base.The command can be used to execute the coordinate precession or to perform transformations between the following coordinate systems:

Proper motion corrections are available.

The routines used for transformations are those of the SLALIB library, courtesy of STARLINK.

INPUT FIELDS of the command:

From: PDB ?

The user must enter Y when the input catalogue is in Personal Data Base.

Example : Y

Catalogue Name

The name of the input catalogue.

Example : UGC

Select:

User must enter the name of the fields of the input catalogue that can be extracted and written in the output file. The field names must be divided by space or by comma. The following special keywords can be used:

%ALL Return all the fields of the input catalogue

%REC Return the record number of the input cat.

Example : RA DEC MAG %REC

The CTRL-L key provides more rows to write field names.

1Coord.

The user must enter here the name of the catalogue field that contains the first coordinate. This is the longitude in a generic longitude/latitude coordinate system. First coordinates in astronomical catalogues are Right Ascension, ecliptic longitude, galactic longitude and so on. These coordinates are the input values for the conversion.

Example : RA

2Coord.

The user must enter here the name of the catalogue's field that contains the second coordinate. This is the latitude in a generic longitude/latitude coordinate system. Second coordinates in astronomical catalogues are declination, ecliptic latitude, galactic latitude and so on. These coordinates are the input values for the conversion.

Example : DEC

Coor. System

The user must enter here a code that defines the system of the coordinates of the input catalogue. When the input data are ecliptic, galactic, or supergalactic coordinates how to select the right code is obvious. In the equatorial system, FK4 is the default for coordinate with equinox prior of year 2000, and FK5 after this date.

The codes are:

4   =   equatorial, FK4
B   =   like FK4,without E-terms
5   =   equatorial, FK5
A   =   equatorial, geocentric apparent
E   =   ecliptic
G   =   galactic
S   =   supergalactic

Example : 4

Eqnox

The user must enter here the equinox year of the coordinate system in input. This field is divided into two subfields. In the first subfield (of one character) the user can select the old or new IAU definition of the beginning of the year with the codes:

B   Old Bessellian year
J   New Julian epochs

The second subfield must be set to the year of precession of the input coordinate system. With catalogues precessed prior of year 2000.00 the Bessellian year is mostly used.

Example : B 1950.00

Proper motion correction ?

Answering yes to this question the user can correct the coordinates conversion for the proper motions. A new window will be created on the screen to request more parameters. To work with the proper motion correction, the epoch of the coordinate acquisition must be known. This can be a global data or a field inside the catalogue that define, for each record, the epoch. Moreover must be presented a couple of fields, inside a catalogue, that define the values of the proper motion, of the two coordinates, in arcsec/year units.

Example : Y

INPUT FIELDS of the window:

Proper motion on 1Coord.

The user must enter here the name of the catalogue field that contains the proper motion on the first coordinate in arcsec/year units. The user can have a list of the names of the fields with the help.

Example : PMRA

Proper motion on 2Coord.

The user must enter here the name of the catalogue field that contains the proper motion on the second coordinate in arcsec/year units. The user can have the list of the names of the fields with the help.

Example : PMDEC

Epoch year

When the epoch is the same for all the records of the catalogue, the user can write here the year, otherwise he can enter the name of the catalogue field that contain epoch.

Example : 1954.00

Then the secondary window is closed.

1Coord.

This field must be filled only if the new catalogue will be inserted in the PDB. The user can enter here the name of the new catalogue's field that will contain the first coordinate. This is the longitude (Right Ascension, ecliptic longitude, galactic longitude and so on) in the new coordinate system selected by the user. A valid name for a coordinate field is a string of eight or less characters that starts with an alphabetic character and that does not contain any special symbols.

Example : RA2000

2Coord.

This field must be filled only if the new catalogue will be inserted in the PDB. The user must enter here the name of the new catalogue's field that will contains the second coordinate. This is the latitude (declination, ecliptic latitude, galactic latitude and so on) in the new coordinate system selected by the user. A valid name for a coordinate field is a string of eight or less characters that starts with an alphabetic character and that does not contain any special symbols.

Example : DEC2000

Coor. System

The user must enter here a code that selects the coordinate system that he needs to create in the output catalogue. When he wants to create ecliptic, galactic or supergalactic coordinate, setting this code is obvious. When the user wants to precess RA and DEC coordinate at an equinox prior of year 2000 he will generally use equatorial FK4 system. FK5 is used for a precession at year 2000 or more.

The codes are:

4   =   equatorial, FK4
B   =   like FK4,without E-terms
5   =   equatorial, FK5
A   =   equatorial, geocentric apparent
E   =   ecliptic
G   =   galactic
S   =   supergalactic

Example : 5

Eqnox

The user must enter here the equinox year of the final coordinate system. This field is divided into two subfields. In the first subfield (of one character) the user can select the old or new IAU definition of the beginning of the year with the codes:

B   Old Bessellian year
J   New Julian epochs

The second subfield will contain the year of precession of the output. With catalogues precessed at a date prior of year 2000.00 the Bessellian year is mostly used.

Example : J 2000.00

Type

The output data can be written in the format hours-minutes-seconds, in degrees, radians and so on. The user can select here the format of the coordinates that he needs. Typically Right Ascension and declination are written in the standard DIRA format, galactic and supergalactic coordinates are in degrees etc. The codes that define the type of data are the following.

1   =   Standard format HHMMSSmmm and sDDPPSSmmm
2   =   Degrees
3   =   Extended format HHMMSSmmm and sDDPPSSmmm
4   =   Radiants

Example : 1

Output: File Name

The name of the output file that contains the fields selected from the input catalogue and the new coordinates created by this task.

Example : NEWCAT2.DAT

PDB Catalogue Name

The name of the new catalogue in the Personal Data Base. When this field is filled an entry in the PDB for this new catalogue will be created and the user can continue to work on these new data with DIRA. Otherwise the output file only will be written. Valid catalogue names are strings of 12 or less characters that does not contains any special symbols.

Example : NEWCAT2

NOTE:

This task works with double precision numbers and is time expensive, moreover does not allows to select data inside sky window, so all the input catalogue is converted in a new one. The user can use DB_SELECT to reduce the size of the catalogue given as input to the DB_COCO.

The new coordinates are written in the output file as the last fields of the record.



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