ILP83-Modified Arc shape definitions so that they will all use direction rather …

…than offset, for consistency.

@@ -291,17 +291,16 @@
                 <tag name="unit" value="meters"/>
                 <comment>inner horizontal radius</comment>
             </elem>
-            <elem name="offset" type="float32" multiplicity="1">
+            <elem name="direction" type="float32" multiplicity="1">
                 <tag name="unit" value="degrees"/>
                 <comment>
-                    Angle between north and start of arc.\n
-                    0 &lt;= offset &lt; 360
+                    Angle from north to center of arc.\n
+                    0 &lt;= direction &lt; 360
                 </comment>
-            </elem>
             <elem name="opening" type="float32" multiplicity="1">
                 <tag name="unit" value="degrees"/>
                 <comment>
-                    Delta angle from offset to end of arc.\n
+                    Horizontal coverage angle of the antenna face; half on either side of direction.\n
                     0 &lt; opening &lt;= 360.
                 </comment>
             </elem>
@@ -334,17 +333,16 @@
                 </comment>
             </elem>
 
-            <elem name="offset" type="float32" multiplicity="1">
+            <elem name="direction" type="float32" multiplicity="1">
                 <tag name="unit" value="degrees"/>
-                <comment>
-                    Angle between north and start of arc.\n
-                    0 &lt;= offset &lt; 360
-                </comment>
-            </elem>
+	            <comment>
+	                Angle from north to center of arc.\n
+	                0 &lt;= direction &lt; 360
+	            </comment>
             <elem name="opening" type="float32" multiplicity="1">
                 <tag name="unit" value="degrees"/>
                 <comment>
-                    delta angle from offset to end of arc.\n
+                    Horizontal coverage angle of the antenna face; half on either side of direction.\n
                     0 &lt; opening &lt;= 360.
                 </comment>
             </elem>