diff -u -r1.2 -r1.3
--- SiStripTrackerBarrel.java	29 Sep 2006 17:41:48 -0000	1.2
+++ SiStripTrackerBarrel.java	29 Sep 2006 21:37:20 -0000	1.3
@@ -114,6 +114,9 @@

 			// Radius of the module center.
 			double rc = rphi_layout.getAttribute("rc").getDoubleValue();
 

+			// The delta radius of every other module.
+			double rphi_dr = rphi_layout.getAttribute("dr").getDoubleValue();
+			

 			// Phi increment for one module.
 			double phi_incr = (Math.PI * 2) / nphi;
 

@@ -132,7 +135,7 @@

 			assert (nz > 0);
 
 			// Radial displacement parameter, of every other module.

-			double dr = z_layout.getAttribute("dr").getDoubleValue();

+			double z_dr = z_layout.getAttribute("dr").getDoubleValue();

 
 			// Z increment for module placement along Z axis.
 			// Adjust for z0 at center of module rather than

@@ -175,11 +178,11 @@

 			for (int ii = 0; ii < nphi; ii++)
 			{
 				// Delta x of module position.

-				double dx = dr * cos(phic + phi_tilt);

+				double dx = z_dr * cos(phic + phi_tilt);

 				
 				// Delta y of module position.

-				double dy = dr * sin(phic + phi_tilt);
-

+				double dy = z_dr * sin(phic + phi_tilt);				
+				

 				// Basic x module position.
 				double x = rc * cos(phic);
 				

@@ -247,6 +250,12 @@

 
 				// Increment the phi placement of module.
 				phic += phi_incr;

+				
+				// Increment the center radius according to dr parameter.
+				rc += rphi_dr;
+				
+				// Flip sign of dr parameter.
+				rphi_dr *= -1;

 
 				// Reset the Z placement parameter for module.
 				module_z = -z0;