==stereographic projection== 

 Hello.  Although the mathematical notation you added to Image:Stereographic.png was useful, I've edited it to conform to Wikipedia conventions in several respects: (1) round brackets rather than square; (2) italicized variables to match TeX style; (3) spacing before and after the minus sign; (4) using a long dash rather than a stubby little hyphen for the minus sign (TeX does (3) and (4) automatically, but I don't know any way of incorporating TeX into figures drawn with xfig).