This is a port of gausskruger.js to PHP packaged as a Yii extension.
gausskruger.js is a library to convert to/from common Swedish coordinate systems and the international WGS84 standard used by most GPS devices today. It can convert
RT90 <-> WGS84 and
SWEREF99 <-> WGS84.
The extension has been tested on Yii 1.1.14. It will probably work on much older versions too as it doesn't really interface with Yii.