GIS spatial functions in PHP?

I need to convert data points from one geographic projection (Lat Long, Mercator, UTM) to another and I wonder if there's a set of PHP tools or functions that can do this? I tried writing one myself based on formulas I found, but it wasn't accurate enough and I can't find better formulas anywhere, so I was wondering if there might be some prepackaged functions somewhere. Failing that, what about something like PROJ.4? Thanks!