diff --git a/materials.xml b/materials.xml
index 5bc85f06f..c47817e14 100644
--- a/materials.xml
+++ b/materials.xml
@@ -2438,12 +2438,14 @@ Shared parameters for various materials.
   <b>0.0</b>
   <a>1.0</a>
  </emissive>
- <object>
-  <path>Models/Trees/coniferous-tree.ac</path>
-  <coverage-m2 alias="/params/forest/single-tree-coverage"/>
+ <object-group>
   <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
+  <object>
+   <path>Models/Trees/coniferous-tree.ac</path>
+   <coverage-m2 alias="/params/forest/single-tree-coverage"/>
+   <heading-type>billboard</heading-type>
+  </object>
+ </object-group>
 </material>
 
 <material>
@@ -2476,12 +2478,14 @@ Shared parameters for various materials.
   <b>0.0</b>
   <a>1.0</a>
  </emissive>
- <object>
-  <path>Models/Trees/deciduous-tree.ac</path>
-  <coverage-m2 alias="/params/forest/single-tree-coverage"/>
+ <object-group>
   <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
+  <object>
+   <path>Models/Trees/deciduous-tree.ac</path>
+   <coverage-m2 alias="/params/forest/single-tree-coverage"/>
+   <heading-type>billboard</heading-type>
+  </object>
+ </object-group>
 </material>
 
 <material>
@@ -2514,18 +2518,15 @@ Shared parameters for various materials.
   <b>0.0</b>
   <a>1.0</a>
  </emissive>
- <object>
-  <path>Models/Trees/deciduous-tree.ac</path>
-  <coverage-m2 alias="/params/forest/double-tree-coverage"/>
+ <object-group>
   <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
- <object>
-  <path>Models/Trees/coniferous-tree.ac</path>
-  <coverage-m2 alias="/params/forest/double-tree-coverage"/>
-  <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
+  <object>
+   <path>Models/Trees/deciduous-tree.ac</path>
+   <path>Models/Trees/coniferous-tree.ac</path>
+   <coverage-m2 alias="/params/forest/tree-coverage"/>
+   <heading-type>billboard</heading-type>
+  </object>
+ </object-group>
 </material>
 
 <material>
@@ -2559,12 +2560,14 @@ Shared parameters for various materials.
   <b>0.0</b>
   <a>1.0</a>
  </emissive>
- <object>
-  <path>Models/Trees/coniferous-tree.ac</path>
-  <coverage-m2 alias="/params/forest/single-tree-coverage"/>
+ <object-group>
   <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
+  <object>
+   <path>Models/Trees/coniferous-tree.ac</path>
+   <coverage-m2 alias="/params/forest/single-tree-coverage"/>
+   <heading-type>billboard</heading-type>
+  </object>
+ </object-group>
 </material>
 
 <material>
@@ -2597,12 +2600,14 @@ Shared parameters for various materials.
   <b>0.0</b>
   <a>1.0</a>
  </emissive>
- <object>
-  <path>Models/Trees/deciduous-tree.ac</path>
-  <coverage-m2 alias="/params/forest/single-tree-coverage"/>
+ <object-group>
   <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
+  <object>
+   <path>Models/Trees/deciduous-tree.ac</path>
+   <coverage-m2 alias="/params/forest/single-tree-coverage"/>
+   <heading-type>billboard</heading-type>
+  </object>
+ </object-group>
 </material>
 
 <material>
@@ -2668,42 +2673,41 @@ Shared parameters for various materials.
   <b>0.0</b>
   <a>1.0</a>
  </emissive>
- <object>
-  <path>Models/Buildings/big-apartment.ac</path>
-  <coverage-m2>10000000</coverage-m2>
+ <object-group>
   <range-m>10000</range-m>
-  <heading-type>fixed</heading-type>
- </object>
- <object>
-  <path>Models/Buildings/small-glass-office-building.ac</path>
-  <coverage-m2>500000</coverage-m2>
+  <object>
+   <path>Models/Buildings/big-apartment.ac</path>
+   <coverage-m2>10000000</coverage-m2>
+   <heading-type>random</heading-type>
+  </object>
+ </object-group>
+ <object-group>
   <range-m>5000</range-m>
-  <heading-type>fixed</heading-type>
- </object>
- <object>
-  <path>Models/Buildings/big-church.ac</path>
-  <coverage-m2>10000000</coverage-m2>
-  <range-m>5000</range-m>
-  <heading-type>fixed</heading-type>
- </object>
- <object>
-  <path>Models/Buildings/water-tower.ac</path>
-  <coverage-m2>50000000</coverage-m2>
-  <range-m>5000</range-m>
-  <heading-type>fixed</heading-type>
- </object>
- <object>
-  <path>Models/Trees/deciduous-tree.ac</path>
-  <coverage-m2>500000</coverage-m2>
+  <object>
+   <path>Models/Buildings/small-glass-office-building.ac</path>
+   <coverage-m2>500000</coverage-m2>
+   <heading-type>random</heading-type>
+  </object>
+  <object>
+   <path>Models/Buildings/big-church.ac</path>
+   <coverage-m2>10000000</coverage-m2>
+   <heading-type>random</heading-type>
+  </object>
+  <object>
+   <path>Models/Buildings/water-tower.ac</path>
+   <coverage-m2>50000000</coverage-m2>
+   <heading-type>random</heading-type>
+  </object>
+ </object-group>
+ <object-group>
   <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
- <object>
-  <path>Models/Trees/coniferous-tree.ac</path>
-  <coverage-m2>1000000</coverage-m2>
-  <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
+  <object>
+   <path>Models/Trees/deciduous-tree.ac</path>
+   <path>Models/Trees/coniferous-tree.ac</path>
+   <coverage-m2>500000</coverage-m2>
+   <heading-type>billboard</heading-type>
+  </object>
+ </object-group>
 </material>
 
 <material>
@@ -2736,36 +2740,33 @@ Shared parameters for various materials.
    <b>0.0</b>
    <a>1.0</a>
   </emissive>
- <object>
-  <path>Models/Buildings/small-glass-office-building.ac</path>
-  <coverage-m2>500000</coverage-m2>
+ <object-group>
   <range-m>5000</range-m>
-  <heading-type>fixed</heading-type>
- </object>
- <object>
-  <path>Models/Buildings/big-church.ac</path>
-  <coverage-m2>10000000</coverage-m2>
-  <range-m>5000</range-m>
-  <heading-type>fixed</heading-type>
- </object>
- <object>
-  <path>Models/Buildings/water-tower.ac</path>
-  <coverage-m2>50000000</coverage-m2>
-  <range-m>5000</range-m>
-  <heading-type>fixed</heading-type>
- </object>
- <object>
-  <path>Models/Trees/deciduous-tree.ac</path>
-  <coverage-m2>250000</coverage-m2>
+  <object>
+   <path>Models/Buildings/small-glass-office-building.ac</path>
+   <coverage-m2>500000</coverage-m2>
+   <heading-type>random</heading-type>
+  </object>
+  <object>
+   <path>Models/Buildings/big-church.ac</path>
+   <coverage-m2>10000000</coverage-m2>
+   <heading-type>random</heading-type>
+  </object>
+  <object>
+   <path>Models/Buildings/water-tower.ac</path>
+   <coverage-m2>50000000</coverage-m2>
+   <heading-type>random</heading-type>
+  </object>
+ </object-group>
+ <object-group>
   <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
- <object>
-  <path>Models/Trees/coniferous-tree.ac</path>
-  <coverage-m2>500000</coverage-m2>
-  <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
+  <object>
+   <path>Models/Trees/deciduous-tree.ac</path>
+   <path>Models/Trees/coniferous-tree.ac</path>
+   <coverage-m2>250000</coverage-m2>
+   <heading-type>billboard</heading-type>
+  </object>
+ </object-group>
 </material>
 
 <material>
@@ -2798,30 +2799,28 @@ Shared parameters for various materials.
   <b>0.0</b>
   <a>1.0</a>
  </emissive>
- <object>
-  <path>Models/Buildings/big-church.ac</path>
-  <coverage-m2>250000</coverage-m2>
+ <object-group>
   <range-m>10000</range-m>
-  <heading-type>fixed</heading-type>
- </object>
- <object>
-  <path>Models/Buildings/water-tower.ac</path>
-  <coverage-m2>1000000</coverage-m2>
-  <range-m>10000</range-m>
-  <heading-type>fixed</heading-type>
- </object>
- <object>
-  <path>Models/Trees/deciduous-tree.ac</path>
-  <coverage-m2>500000</coverage-m2>
+  <object>
+   <path>Models/Buildings/big-church.ac</path>
+   <coverage-m2>250000</coverage-m2>
+   <heading-type>random</heading-type>
+  </object>
+  <object>
+   <path>Models/Buildings/water-tower.ac</path>
+   <coverage-m2>1000000</coverage-m2>
+   <heading-type>random</heading-type>
+  </object>
+ </object-group>
+ <object-group>
   <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
- <object>
-  <path>Models/Trees/coniferous-tree.ac</path>
-  <coverage-m2>1000000</coverage-m2>
-  <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
+  <object>
+   <path>Models/Trees/deciduous-tree.ac</path>
+   <path>Models/Trees/coniferous-tree.ac</path>
+   <coverage-m2>500000</coverage-m2>
+   <heading-type>billboard</heading-type>
+  </object>
+ </object-group>
 </material>
 
 <material>
@@ -3148,30 +3147,31 @@ Shared parameters for various materials.
   <b>0.0</b>
   <a>1.0</a>
  </emissive>
- <object>
-  <path>Models/Buildings/red-barn.ac</path>
-  <coverage-m2>5000000</coverage-m2>
+ <object-group>
   <range-m>5000</range-m>
-  <heading-type>fixed</heading-type>
- </object>
- <object>
-  <path>Models/Fauna/cow.ac</path>
-  <coverage-m2>10000</coverage-m2>
+  <object>
+   <path>Models/Buildings/red-barn.ac</path>
+   <coverage-m2>5000000</coverage-m2>
+   <heading-type>random</heading-type>
+  </object>
+ </object-group>
+ <object-group>
   <range-m>1000</range-m>
-  <heading-type>fixed</heading-type>
- </object>
- <object>
-  <path>Models/Trees/deciduous-tree.ac</path>
-  <coverage-m2>500000</coverage-m2>
+  <object>
+   <path>Models/Fauna/cow.ac</path>
+   <coverage-m2>10000</coverage-m2>
+   <heading-type>random</heading-type>
+  </object>
+ </object-group>
+ <object-group>
   <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
- <object>
-  <path>Models/Trees/coniferous-tree.ac</path>
-  <coverage-m2>1000000</coverage-m2>
-  <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
+  <object>
+   <path>Models/Trees/deciduous-tree.ac</path>
+   <path>Models/Trees/coniferous-tree.ac</path>
+   <coverage-m2>500000</coverage-m2>
+   <heading-type>billboard</heading-type>
+  </object>
+ </object-group>
 </material>
 
 <material>
@@ -3204,30 +3204,31 @@ Shared parameters for various materials.
   <b>0.0</b>
   <a>1.0</a>
  </emissive>
- <object>
-  <path>Models/Buildings/red-barn.ac</path>
-  <coverage-m2>5000000</coverage-m2>
+ <object-group>
   <range-m>5000</range-m>
-  <heading-type>fixed</heading-type>
- </object>
- <object>
-  <path>Models/Fauna/cow.ac</path>
-  <coverage-m2>10000</coverage-m2>
+  <object>
+   <path>Models/Buildings/red-barn.ac</path>
+   <coverage-m2>5000000</coverage-m2>
+   <heading-type>random</heading-type>
+  </object>
+ </object-group>
+ <object-group>
   <range-m>1000</range-m>
-  <heading-type>fixed</heading-type>
- </object>
- <object>
-  <path>Models/Trees/deciduous-tree.ac</path>
-  <coverage-m2>500000</coverage-m2>
+  <object>
+   <path>Models/Fauna/cow.ac</path>
+   <coverage-m2>10000</coverage-m2>
+   <heading-type>random</heading-type>
+  </object>
+ </object-group>
+ <object-group>
   <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
- <object>
-  <path>Models/Trees/coniferous-tree.ac</path>
-  <coverage-m2>1000000</coverage-m2>
-  <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
+  <object>
+   <path>Models/Trees/deciduous-tree.ac</path>
+   <path>Models/Trees/coniferous-tree.ac</path>
+   <coverage-m2>500000</coverage-m2>
+   <heading-type>billboard</heading-type>
+  </object>
+ </object-group>
 </material>
 
 <material>
@@ -3260,30 +3261,31 @@ Shared parameters for various materials.
   <b>0.0</b>
   <a>1.0</a>
  </emissive>
- <object>
-  <path>Models/Buildings/red-barn.ac</path>
-  <coverage-m2>5000000</coverage-m2>
+ <object-group>
   <range-m>5000</range-m>
-  <heading-type>fixed</heading-type>
- </object>
- <object>
-  <path>Models/Fauna/cow.ac</path>
-  <coverage-m2>10000</coverage-m2>
+  <object>
+   <path>Models/Buildings/red-barn.ac</path>
+   <coverage-m2>5000000</coverage-m2>
+   <heading-type>random</heading-type>
+  </object>
+ </object-group>
+ <object-group>
   <range-m>1000</range-m>
-  <heading-type>fixed</heading-type>
- </object>
- <object>
-  <path>Models/Trees/deciduous-tree.ac</path>
-  <coverage-m2>500000</coverage-m2>
+  <object>
+   <path>Models/Fauna/cow.ac</path>
+   <coverage-m2>10000</coverage-m2>
+   <heading-type>random</heading-type>
+  </object>
+ </object-group>
+ <object-group>
   <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
- <object>
-  <path>Models/Trees/coniferous-tree.ac</path>
-  <coverage-m2>1000000</coverage-m2>
-  <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
+  <object>
+   <path>Models/Trees/deciduous-tree.ac</path>
+   <path>Models/Trees/coniferous-tree.ac</path>
+   <coverage-m2>500000</coverage-m2>
+   <heading-type>billboard</heading-type>
+  </object>
+ </object-group>
 </material>
 
 <material>
@@ -3316,18 +3318,15 @@ Shared parameters for various materials.
   <b>0.0</b>
   <a>1.0</a>
  </emissive>
- <object>
-  <path>Models/Trees/deciduous-tree.ac</path>
-  <coverage-m2>500000</coverage-m2>
+ <object-group>
   <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
- <object>
-  <path>Models/Trees/coniferous-tree.ac</path>
-  <coverage-m2>1000000</coverage-m2>
-  <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
+  <object>
+   <path>Models/Trees/deciduous-tree.ac</path>
+   <path>Models/Trees/coniferous-tree.ac</path>
+   <coverage-m2>500000</coverage-m2>
+   <heading-type>billboard</heading-type>
+  </object>
+ </object-group>
 </material>
 
 <material>
@@ -3360,18 +3359,15 @@ Shared parameters for various materials.
   <b>0.0</b>
   <a>1.0</a>
  </emissive>
- <object>
-  <path>Models/Trees/deciduous-tree.ac</path>
-  <coverage-m2>200000</coverage-m2>
+ <object-group>
   <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
- <object>
-  <path>Models/Trees/coniferous-tree.ac</path>
-  <coverage-m2>200000</coverage-m2>
-  <range-m alias="/params/forest/tree-range-m"/>
-  <heading-type>billboard</heading-type>
- </object>
+  <object>
+   <path>Models/Trees/deciduous-tree.ac</path>
+   <path>Models/Trees/coniferous-tree.ac</path>
+   <coverage-m2>200000</coverage-m2>
+   <heading-type>billboard</heading-type>
+  </object>
+ </object-group>
 </material>
 
 <material>