Roman pots

Right now, the code generates a RP unit which is a pair of two Pots and the description has a boolean that rotates the whole unit by 90 degrees. The description also allows for variable detector insertion depth, and support, detector and frame dimensions (the frame is not yet implemented in code - I have to meditate a bit more on that).

It compiles but throws a runtime error, probably because of the XML parsing (there's a FIXME in the code). That should be fixed soon.

The next step is to add layers into a single detector. That will be easy once I'm happy with the current state.

Just so you're notified, @whit.

src/GenericDetectors/trackers/compact/RomanPot_example.xml

+<lccdd xmlns:compact="http://www.lcsim.org/schemas/compact/1.0" 
+       xmlns:xs="http://www.w3.org/2001/XMLSchema" 
+       xs:noNamespaceSchemaLocation="http://www.lcsim.org/schemas/compact/1.0/compact.xsd">
+  <info name="RomanPot_example" title="Roman Pot detector example"
+        author="Tomas Polakovic"
+        url="https://eicweb.phy.anl.gov/EIC/NPDet"
+        status="development"
+        version="$Id: compact.xml v1.0 2016-12-21$">
+    <comment>A simplified Roman pot detector</comment>        
+  </info>
+
+  <includes>
+    <gdmlFile  ref="elements.xml"/>
+    <gdmlFile  ref="materials.xml"/>
+  </includes>
+  
+  <define>
+    <constant name="world_side" value="10*m"/>
+    <constant name="world_x" value="world_side"/>
+    <constant name="world_y" value="world_side"/>
+    <constant name="world_z" value="world_side"/>
+    
+    <constant name="CrossingAngle" value="0.020*rad"/>
+  </define>
+
+  <limits>
+    <limitset name="cal_limits">
+      <limit name="step_length_max" particles="*" value="5.0" unit="mm" />
+    </limitset>
+    <limitset name="SimpleRomanPotRegionLimitSet">
+      <limit name="step_length_max" particles="*" value="1.0" unit="mm" />
+      <limit name="track_length_max" particles="*" value="1.0" unit="mm" />
+      <limit name="time_max" particles="*" value="0.1" unit="ns" />
+      <limit name="ekin_min" particles="*" value="0.001" unit="MeV" />
+      <limit name="range_min" particles="*" value="0.1" unit="mm" />
+    </limitset>
+  </limits>
+  <regions>
+    <region name="SimpleRomanPotRegion" eunit="MeV" lunit="mm" cut="0.0001" threshold="0.0001">
+      <limitsetref name="SimpleRomanPotRegionLimitSet"/>
+    </region>
+  </regions>
+
+  <comment>Common Generic visualization attributes</comment>
+  <display>
+    <vis name="InvisibleNoDaughters"      showDaughters="false" visible="false"/>
+    <vis name="InvisibleWithDaughters"    showDaughters="true" visible="false"/>
+    <vis name="GreenVis"       alpha="0.5"  r= "0.0" g="1.0" b="0.0" showDaughters="true" visible="true"/>
+    <vis name="RedVis"         alpha="0.0"  r= "1.0" g="0.0" b="0.0" showDaughters="true" visible="true"/>
+    <vis name="BlueVis"        alpha="0.0"  r= "0.0" g="0.0" b="1.0" showDaughters="true" visible="true"/>
+    <vis name="OrangeVis"      alpha="0.5"  r= "1.0" g="0.45" b="0.0" showDaughters="true" visible="true"/>
+    <vis name="RedGreenVis"    alpha="0.5"  r= "1.0" g="1.0" b="0.0" showDaughters="true" visible="true"/>
+    <vis name="BlueGreenVis"   alpha="0.5"  r= "0.0" g="1.0" b="1.0" showDaughters="true" visible="true"/>
+    <vis name="PurpleVis"      alpha="0.5"  r= "1.0" g="0.0" b="1.0" showDaughters="true" visible="true"/>
+    <vis name="DoubleRedG"     alpha="0.5"  r= "2.0" g=".10" b="0.0" showDaughters="true" visible="true"/>
+    <vis name="RBG015"         alpha="0.5"  r= "0.0" g=".2"  b="1.0" showDaughters="true" visible="true"/>
+    <vis name="RBG510"         alpha="0.5"  r= "1.0" g=".2"  b="0.0" showDaughters="true" visible="true"/>
+    <vis name="RBG"            alpha="0.5"  r= "1.0" g="1.0" b="1.0" showDaughters="true" visible="true"/>
+    <vis name="GrayVis"        alpha="0.5"  r= "0.75" g="0.75" b="0.75" showDaughters="true" visible="true"/>
+  </display>
+
+  <detectors>
+    <detector id = "1" name = "MyRomanPot" type = "RomanPot" readout =
+              "ForwardRomanPotHits" vis = "RedVis">
+      <dimensions x = "3.0*cm" y = "3.0*cm" z = "0.03*cm" delta = "0.005*cm" />
+      <support z = "1*mm" />
+      <frame x = "10.0*cm" y = "5.0*cm" z = "2*cm" />
+      <position z_offset = "0.0*m" rotation = "false" vmax = "10*cm" v = "2.0*cm" />
+      <layer repeat = "5">
+        <slice material = "Carbon"  thickness = "0.5*mm"  vis = "BlueVis" />
+        <slice material = "Silicon" thickness = "0.03*cm" vis = "GreenVis" sensitive = "true"  />
+        <slice material = "Carbon"  thickness = "0.5*mm"  vis = "BlueVis" />
+        <slice material = "Vacuum"  thickness = "1.0*mm"  vis = "InvisibleWithDaughters" />
+      </layer>
+    </detector>
+  </detectors>
+
+  <!--  Definition of the readout segmentation/definition  -->
+  <readouts>
+    <readout name="ForwardRomanPotHits">
+      <!-- <id>system:5,element:5,layer:4,module:14,sensor:2,side:32:-2,strip:24</id> -->
+      <id>system:5,element:5,layer:4,slice:5</id>
+    </readout>
+  </readouts>
+
+  <plugins>
+    <!--
+    <plugin name="DD4hep_GenericSurfaceInstallerPlugin">
+      <argument value="MyRomanPot"/>
+      <argument value="dimension=2"/>
+      <argument value="u_x=-1."/>
+      <argument value="v_y=-1."/>
+      <argument value="n_z=1."/>
+    </plugin>	
+    -->
+    <plugin name="InstallSurfaceManager"/>
+  </plugins>
+
+  <fields>
+    <field name="GlobalSolenoid" type="solenoid" 
+      inner_field="4.0*tesla"
+      outer_field="-0.6*tesla" 
+      zmax="3*m"
+      outer_radius="2*m">
+    </field>
+  </fields>
+</lccdd>