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diff --git a/Documentation/figures/4S+2D_reciproque3.pov b/Documentation/figures/4S+2D_reciproque3.pov
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+#include "colors.inc"    // The include files contain
+#include "textures.inc"  // pre-defined scene elements
+#include "glass.inc"
+#include "metals.inc"
+#include "skies.inc"
+#include "shapes.inc"
+#include "bravais.inc"
+#include "arrows.inc"
+
+// the cristal lattice
+#declare a = <1,0,0>;
+#declare b = <.31,.95,0>;
+#declare c = <.4,.5,0.76>;
+
+#declare camera_location = 5 * (x+y+.5*z)+ 3*z + y;
+#declare camera_look_at = <0,0,0>+3*z + y;
+
+//#declare camera_location = a/2+b/1.5-2*z;
+//#declare camera_look_at = a/2+b/1.5;
+
+global_settings{ max_trace_level 255 }
+
+background { color DarkGreen }
+
+// all setup
+camera {
+  orthographic
+  location camera_location
+  look_at camera_look_at
+}
+
+light_source {
+	<10, 0, 0> 
+	color White
+        parallel
+        point_at <0, 0, 0>
+        shadowless
+}
+light_source {
+	<0, 10, 0> 
+	color White
+        parallel
+        point_at <0, 0, 0>
+}
+light_source {
+	<0, 0, 10> 
+	color White
+        parallel
+        point_at <0, 0, 0>
+}
+
+union{
+  plane { <1,0,0>, -3 pigment {color LightWood} }
+  plane { <0,1,0>, 0 pigment {color LightWood*.9 transmit .3} }
+  plane { <0,0,1>, 0 pigment {color LightWood*.8 transmit .3}}
+}
+
+// the tree principals directions
+cylinder{<0,0,-10>,<0,0,10>, .01 pigment {color Grey}}
+cylinder{<0,-10,0>,<0,10,0>, .01 pigment {color Grey}}
+cylinder{<-10,0,0>,<10,0,0>, .01 pigment {color Grey}}
+
+// the Ewald construction
+#macro ewald(ki, gamma, delta, Alpha, phi)
+  #local kf=vrotate(vrotate(ki, delta*x), -gamma*y);
+  #local Q=kf-ki;
+  #local n = vrotate(vrotate(vlength(Q)*x, Alpha*y), phi*z);
+
+  // plot the ki and kf vectors
+  union{
+    arrow(ki, Blue)
+    arrow(kf, Green)
+    
+    // angle 2theta
+    //object{sector(ki,kf, Yellow, .2) no_shadow}
+    
+    // angle delta
+    //object{sector(kf, kf.x*x+kf.z*z, Red, .6) no_shadow}
+    // angle gamma
+    //object{sector(ki, kf.x*x+kf.z*z, Blue, .6) no_shadow}
+    translate -ki
+  }
+  
+  // the diffraction vector Q
+  arrow(Q, Red)
+  
+  // angle vartheta
+  //object{secteur(x, Q.x*x+Q.y*y, Magenta, .5)}
+  
+  // angle tau
+  object{sector(Q, n, ForestGreen, .5) no_shadow}
+
+  // angle psi
+  object{arrow_circular(Q, .5, .05, 0, 90, 1, Red) translate 1.1*Q no_shadow}
+
+  arrow(n, Yellow)
+  //disc {0, vcross(ki, Q), vlength(Q) pigment{color Red+Blue transmit .1}}
+  disc {0, Q, vlength(Q) pigment{color Red transmit .3}}
+  //plane { <0,0,-1>, 0 pigment {color LightWood*.2 transmit .7} }
+  
+  // sphères d'ewald
+  merge{
+    sphere{0, vlength(Q) pigment {color Blue transmit .73}}
+    sphere{-ki, vlength(ki) pigment {color Green transmit .93}}
+    no_shadow
+  }
+#end
+
+ewald(-3*z, -30, 40, -60, 30)
+
+// Repère orthonormé de la ligne cristal de soleil.
+object{repere_soleil translate 7.5*z no_shadow}