I'm trying to style some OSM data such that short fences, walls, etc just don't render. I only want to display barriers over some certain length. I've tried this rule,
tags LIKE '%barrier%' AND ($length > 100)
and quite a few variations on it, finally getting
tags LIKE '%barrier%' AND $length > 0.001
to do about what I want. Clearly, I don't know what units this is measuring in. It was awkward getting it to work though because while the "test" button next to the formula always gave me no results, the actual map stopped drawing the shorter fences like I wanted.
Indeed, the test button doesn't seem to want to work with any length attribute, as even
tags LIKE '%barrier%' AND $length != 0
returns "no results". So I guess my question now is: Am I doing something wrong, or is this a bug?