astropy/astropy — pull request #3230 by sargas (2014-12-18 17:16:25+00:00)
Title: Add support for specifying the axis when obtaining a wcs pixel scale

Simple change. There didn't seem to be any disagreement to @mcara's suggestion in #3113 to use the geometric mean. This PR does that and adds a `which=` kwarg for obtaining a the pixel scale in a specific diminsion, and @nden's suggestion of exposing the pixel scale for each diminsion.