missing properties and a terminator

- define missing property-definitions for the skydome shader
- introduce a property rule for terminator-relative-position-m
  for local weather

Environment/environment.xml

@@ -334,4 +334,10 @@
     </config>
   </sea>
 
+  <!-- definitions for the scattering skydome shader -->
+  <ground-visibility-m type="double" userarchive="n">16000.0</ground-visibility-m>
+  <ground-haze-thickness-m type="double" userarchive="n">2000.0</ground-haze-thickness-m>
+  <terminator-relative-position-m type="double" userarchive="n">1000000.0</terminator-relative-position-m>
+  <mean-terrain-elevation-m type="double" userarchive="n">0.0</mean-terrain-elevation-m>
+
 </PropertyList>

Environment/local-weather-rules.xml

@@ -0,0 +1,39 @@
+<?xml version="1.0" ?>
+<!--
+ This file is part of FlightGear, the free flight simulator
+ http://www.flightgear.org/
+
+ Copyright (C) 2012 Torsten Dreyer, Torsten (at) t3r _dot_ de
+
+ This program is free software; you can redistribute it and/or
+ modify it under the terms of the GNU General Public License as
+ published by the Free Software Foundation; either version 2 of the
+ License, or (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful, but
+ WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ General Public License for more details.
+-->
+<!--
+  Compute local weather related properties
+-->
+<PropertyList>
+
+  <!-- (pi/2 - /sim/time/sun-angle-rad) / 0.017451 * 110000.0 -->
+  <filter>
+    <name>LocalWeather:terminator-relative-position</name>
+    <input>
+      <expression>
+        <difference>
+          <value>1.57079632675</value>
+          <property>/sim/time/sun-angle-rad</property>
+        </difference>
+      </expression>
+    </input>
+    <output>/environment/terminator-relative-position-m</output>
+    <type>gain</type>
+    <gain>6303363.70409</gain> 
+  </filter>
+
+</PropertyList>

preferences.xml

@@ -382,6 +382,10 @@ Started September 2000 by David Megginson, david@megginson.com
 				<name>Environment Interpolation Rule</name>
 				<path>Environment/interpolator.xml</path>
 			</property-rule>
+			<property-rule>
+				<name>Local Weather Rules </name>
+				<path>Environment/local-weather-rules.xml</path>
+			</property-rule>
 		</systems>
 		<instrumentation>
 			<path>Aircraft/Generic/generic-instrumentation.xml</path>