diff -ur ../gnuplot-4.6.1_orig/gnuplot-4.6.1/src/graph3d.c gnuplot-4.6.1/src/graph3d.c
--- ../gnuplot-4.6.1_orig/gnuplot-4.6.1/src/graph3d.c	2012-09-20 21:56:45.000000000 +0200
+++ gnuplot-4.6.1/src/graph3d.c	2012-12-07 14:50:51.000000000 +0100
@@ -684,6 +684,7 @@
 	if (aspect_ratio_3D >= 3)
 	    zscale3d = xscale3d;
     }
+    zcenter3d =  -(ceiling_z - floor_z) / 2.0 * zscale3d + 1; // without this the rotation-center is located at the bottom of the plot, now it is in the middle
 
     /* Initialize palette */
     if (!quick) {