How to create a 'custom field', similar to a 'custom segmentation' in SSA?

Product Feature: Run queries
Portrait Self Service Analytics is an obsolete product that is no longer supported.

In Portrait Self Service Analytics (SSA) you can create 'custom measures' and 'custom segmentations' - these are separate entities and used in different ways.

A 'custom segmentation' acts on an existing field in your query, and is effectively a way to change the binning/grouping of data values for that field.

A 'custom measure' is a calculation acting on a query result, it is an operation on an existing query measure.

There is no way to create a 'custom field' in SSA.

If you want to create a completely new field to use as a segmentation, then you need to derive that field in your focus in Portrait Miner, before publishing the focus to SSA.
UPDATED:  September 4, 2017