DB_COUNT

COMMAND TYPE : SELECTION

PURPOSE:

Counts the number of objects that satisfy the defined constraints.

DESCRIPTION:

This command counts the number of objects in a catalogue that satisfy constraints imposed on the fields, moreover can evaluate the maximum, the minimum, the average and the RMS of a numerical field.

Typically this task is used when the user wants to know how many objects there are in a sky region or how many objects have a given value in a field.

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

Variable:

This field can be filled when the user wants to know maximum, minimum, and average value of a numerical field.

Example : RADVEL

Evaluate sigma ?

When the user wants to know the RMS of the already defined numerical field he must answer Y to this question.

Example : Y

Where

The user must insert the constraints on the fields of the input catalogue that will be used for the search. The task will count the record that satisfies the constraint. Refer to Query Language chapter to have explanation about the statements and the available functions. The user can set constraints on all the fields of the input catalogue and on function of it, but this is not easy to set constraints on coordinates in this way.

Example : MAG < 13 AND (MAG-MAGV) < 1.5

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

Set/Modify constraints on coordinates ?

The user can set constraints on the coordinates answering Y to this questions. A new window will be opened on the screen and the user will define the name of the coordinate fields and the limits of the sky region. When coordinate constraints are defined these remain active even if this field is set to N. The only way to remove the constraints is to set to zero all the values of the limits.

Example : Y

INPUT FIELDS of the coordinate window:

1Coordinate

The user must enter here the name of the first coordinate of the sky zone that he needs to select. First coordinates can be Right Ascension, galactic longitude and so on.

Example : RA

>From : To:

The user must enter the limits of the sky zone on the first coordinate. A message on the screen shows the units to be used (hours or degrees). When both these fields are set to 0 0 0 the sky zone has not bound in the first coordinate.

Example : 10 20 35.00 10 45 00.00

2Coordinate

The user must enter here the name of the second coordinate of the sky zone that he needs to select. Second coordinates can be declination, galactic latitude and so on.

Example : DEC

>From : To:

The user must enter the limits on the second coordinate of the sky zone. Units are degrees. The values must be entered from South to North. When both this fields are set to 0 0 0 the sky zone has not bound in the second coordinate.

Example : -30 20 00.00 -27 20 00.00

NOTE:

This task does not produce output on file, but writes the output only on the screen.



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