Defining New Attributes

New attributes of data items can be easily created from mathematical operations on existing attributes. In this section, we define new attributes for the W5 Point Source catalog from the tutorial.

To start off, click on the Arithmetic Attributes tool in the toolbar:

A new window will appear for defining attributes. To start off, use the drop-down menu to select the dataset for which you want to create an arithmetic attribute. Then, click on New arithmetic attribute, which will open up the equation editor. From here, set the new attribute name, then type the expression in the box provided. Attribute names should be included in curly brackets, e.g. {ID}. You can either type attribute names directly, using tab-completion if necessary, or you can also select an attribute from the list of available attributes and click on Insert to insert it into the expression.

Here we define a new attribute J - K to be the difference between the J and the Ks magnitudes:

After clicking OK, the new attribute is listed in the list of arithmetic attributes:

At this point, you could if you wished define additional attributes, or go back and edit existing ones. Clicking OK again will return to the main glue interface, from which you can now use the new arithmetic attribute(s).

Note that the expression line can include Numpy functions (prefaced with np.), and anything else you import in your config.py file for Glue. For example, you could define a normalized version of Jmag using: