Eycos USER GUIDE Manual de usuario descargar pdf (Pagina 54)

Specific functions

 FILLCIRCLE: filled circle;

 FIXEDCIRCLE : Circle with a fixed size (not relative to the zoom value in the view);

 PM: arrow for which the orientation and the size are a function of two angles

indicating a proper motion;

 LINE: drawing of a line segment, very useful to display the results of a correlation

between two catalogues.

The CIRCLE, FILLCIRCLE and RAINBOW functionalities take two optional parameters

giving the minimum and maximum parameters used to draw. For example: draw

CIRCLE(${A},1,10) will draw circles proportional to the “A” column values, the

smallest circle will have a 1 pixel radius, the largest circle 10 pixels (in 1x zoom).

If the “draw” action is on a string (e.g. draw "star") or on a reference to a column

(e.g. draw ${ObjectClass}), the string of the column value will be displayed.

Column names or UCD

The reference to a column name is usually done with the column name using the $

{COLUMN_NAME} syntax. This method implies that the filter is more or less

dedicated to a specific catalogue since one needs to know explicitly the column names.

In order to describe filters in a more generic manner, for example taking into account

the magnitude independently of the column name given by the author, Aladin uses UCD.

UCDs or “Unified Content Descriptors” characterize columns independently of

catalogues. For each column, a UCD was associated and gives you the physical quantity

associated to the column. For example, a column with magnitudes will be labelled with

the “pos.mag” UCD. The UCD’s list is maintained by an international committee and is

available here: http://www.ivoa.net/Documents/latest/UCDlistMaintenance.html. Most

of the astronomical servers give their catalogues in VOTable and already contain these

valuable UCDs.

When a filtering rule uses a UCD, the used syntax is $[UCD]. Jokers characters ‘*’ et ‘ ?’

are authorized. For example, $[phot*] corresponds to the first column having a UCD

that starts with “phot”, that is the first column having magnitude measures.

In summary, referencing a column with its name is called with “{}” brackets while

referencing a column with its UCD is called with “[]” brackets.

Example: Drawing a circle proportional to the magnitude for all sources

brighter than 12

$[phot*]<12 { draw circle(-$[phot*]) }

In order to simplify references to columns, the edit board for filters offers two buttons

“Columns” and “UCDs” that enable you to choose in a list the column name, or the UCD

respectively, so that the corresponding text will be automatically written at the cursor’s

location in the edition window.

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Eycos USER GUIDE Manual de usuario Pagina 54