Few more comments to this commit. Re #4403

Code/Mantid/scripts/SANS/isis_instrument.py

@@ -609,23 +609,32 @@ def  move_components(self, ws, xbeam, ybeam):
             @return: the locations of (in the new coordinates) beam center, center of detector bank
         """
 
+        # Store the name of the current detector since temporarily
+        # below set current detector to manual to move both front and rear
+        # detectors
         temp = self.cur_detector().name()
 
+
+        # Deal with front detector
+
         self.setDetector('front-detector')
         # rotate front detector according to value in log file and correction value provided in user file
         rotateDet = (-self.FRONT_DET_ROT - self.cur_detector().rot_corr)
         RotateInstrumentComponent(ws, self.cur_detector().name(), X="0.", Y="1.0", Z="0.", Angle=rotateDet)       
         RotRadians = math.pi*(self.FRONT_DET_ROT + self.cur_detector().rot_corr)/180.
-        # I don't understand why the x-shift of the front detector is depending on the x-position
-        # of the rear detector
+        # x-position of rear detector is an indicator of the beam position...
         xshift = (self.REAR_DET_X + self.other_detector().x_corr - self.FRONT_DET_X - self.cur_detector().x_corr + self.FRONT_DET_RADIUS*math.sin(RotRadians) )/1000. - self.FRONT_DET_DEFAULT_X_M - xbeam
         yshift = (self.cur_detector().y_corr/1000.  - ybeam)
+        # Note don't understand the comment below
         # default in instrument description is 23.281m - 4.000m from sample at 19,281m !
         # need to add ~58mm to det1 to get to centre of detector, before it is rotated.
         zshift = (self.FRONT_DET_Z + self.cur_detector().z_corr + self.FRONT_DET_RADIUS*(1 - math.cos(RotRadians)) )/1000.
         zshift -= self.FRONT_DET_DEFAULT_SD_M
         MoveInstrumentComponent(ws, self.cur_detector().name(), X = xshift, Y = yshift, Z = zshift, RelativePosition="1")
 
+
+        # deal with rear detector
+
         self.setDetector('rear-detector')        
         xshift = -xbeam
         yshift = -ybeam
@@ -634,8 +643,10 @@ def  move_components(self, ws, xbeam, ybeam):
         mantid.sendLogMessage("::SANS:: Setup move "+str(xshift*1000.)+" "+str(yshift*1000.)+" "+str(zshift*1000.))
         MoveInstrumentComponent(ws, self.cur_detector().name(), X = xshift, Y = yshift, Z = zshift, RelativePosition="1")
 
+        # set the current detector back to that it was at the start of this method    
         self.setDetector(temp)    
 
+
         super(SANS2D, self).move_components(ws)
 
         #this implements the TRANS/TRANSPEC=4/SHIFT=... line, this overrides any other monitor move