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diff --git a/buch/papers/kugel/figures/povray/curvature.pov b/buch/papers/kugel/figures/povray/curvature.pov
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+//
+// curvature.pov
+//
+// (c) 2022 Prof Dr Andreas Müller, OST Ostschweizer Fachhochschule
+//
+
+#version 3.7;
+#include "colors.inc"
+
+global_settings {
+	assumed_gamma 1
+}
+
+#declare imagescale = 0.09;
+
+camera {
+	location <10, 10, -40>
+	look_at <0, 0, 0>
+	right 16/9 * x * imagescale
+	up y * imagescale
+}
+
+light_source {
+	<-10, 10, -40> color White
+	area_light <1,0,0> <0,0,1>, 10, 10
+	adaptive 1
+	jitter
+}
+
+sky_sphere {
+	pigment {
+		color rgb<1,1,1>
+	}
+}
+
+//
+// draw an arrow from <from> to <to> with thickness <arrowthickness> with
+// color <c>
+//
+#macro arrow(from, to, arrowthickness, c)
+#declare arrowdirection = vnormalize(to - from);
+#declare arrowlength = vlength(to - from);
+union {
+	sphere {
+		from, 1.1 * arrowthickness
+	}
+	cylinder {
+		from,
+		from + (arrowlength - 5 * arrowthickness) * arrowdirection,
+		arrowthickness
+	}
+	cone {
+		from + (arrowlength - 5 * arrowthickness) * arrowdirection,
+		2 * arrowthickness,
+		to,
+		0
+	}
+	pigment {
+		color c
+	}
+	finish {
+		specular 0.9
+		metallic
+	}
+}
+#end
+
+arrow(<-3.1,0,0>, <3.1,0,0>, 0.01, White)
+arrow(<0,-1,0>, <0,1,0>, 0.01, White)
+arrow(<0,0,-2.1>, <0,0,2.1>, 0.01, White)
+
+#include "curvature.inc"
+
+#declare sigma = 1;
+#declare s = 1.4;
+#declare N0 = 0.4;
+#declare funktion = function(r) {
+	(exp(-r*r/(sigma*sigma)) / sigma
+	-
+	exp(-r*r/(2*sigma*sigma)) / (sqrt(2)*sigma)) / N0
+};
+#declare hypot = function(xx, yy) { sqrt(xx*xx+yy*yy) };
+
+#declare Funktion = function(x,y) { funktion(hypot(x+s,y)) - funktion(hypot(x-s,y)) };
+#macro punkt(xx,yy)
+	<xx, Funktion(xx, yy), yy>
+#end
+
+#declare griddiameter = 0.006;
+union {
+	#declare xmin = -3;
+	#declare xmax = 3;
+	#declare ymin = -2;
+	#declare ymax = 2;
+
+
+	#declare xstep = 0.2;
+	#declare ystep = 0.02;
+	#declare xx = xmin;
+	#while (xx < xmax + xstep/2)
+		#declare yy = ymin;
+		#declare P = punkt(xx, yy);
+		#while (yy < ymax - ystep/2)
+			#declare yy = yy + ystep;
+			#declare Q = punkt(xx, yy);
+			sphere { P, griddiameter }
+			cylinder { P, Q, griddiameter }
+			#declare P = Q;
+		#end
+		sphere { P, griddiameter }
+		#declare xx = xx + xstep;
+	#end
+
+	#declare xstep = 0.02;
+	#declare ystep = 0.2;
+	#declare yy = ymin;
+	#while (yy < ymax + ystep/2)
+		#declare xx = xmin;
+		#declare P = punkt(xx, yy);
+		#while (xx < xmax - xstep/2)
+			#declare xx = xx + xstep;
+			#declare Q = punkt(xx, yy);
+			sphere { P, griddiameter }
+			cylinder { P, Q, griddiameter }
+			#declare P = Q;
+		#end
+		sphere { P, griddiameter }
+		#declare yy = yy + ystep;
+	#end
+
+	pigment {
+		color rgb<0.8,0.8,0.8>
+	}
+	finish {
+		metallic
+		specular 0.8
+	}
+}
+