Fixed typo in projection documentation.

doc/pannellum-equirectangular-projection-reference.tex

@@ -17,8 +17,8 @@ viewed from behind the camera, the y-axis parallel to the camera's vertical
 axis with positive upward as viewed from behind the camera, and the z-axis be
 perpendicular to these two axes with positive extending away from the
 camera.\footnote{Note that this is a left-handed coordinate system.}
-Let \(\lambda\) represent the panorama's latitude, \(\phi\) the panorama's
-longitude, \(\theta\) the latitudinal offset, \(\psi\) the longitudinal offset,
+Let \(\lambda\) represent the panorama's longitude, \(\phi\) the panorama's
+latitude, \(\theta\) the latitudinal offset, \(\psi\) the longitudinal offset,
 and \(f\) the focal length. Let \(\mathbf{a}\) represent a point's position
 vector, \(\mathrm{R}_x(\theta)\) the latitudinal rotation matrix,
 \(\mathbf{d}\) a point's position vector in the camera's reference frame, \(x\)