Allow PeaksWorkspace createPeakQSample to calculate goniometer for CW

Moved code from FindPeaksMD into new method on Goniometer. Then added option onto peaks workspace.

Framework/DataObjects/src/PeaksWorkspace.cpp

@@ -16,6 +16,7 @@
 #include "MantidKernel/PhysicalConstants.h"
 #include "MantidKernel/Quat.h"
 #include "MantidKernel/Unit.h"
+#include "MantidKernel/UnitConversion.h"
 #include "MantidKernel/V3D.h"
 
 #include <algorithm>
@@ -278,7 +279,26 @@ PeaksWorkspace::createPeak(const Kernel::V3D &position,
  */
 Peak *PeaksWorkspace::createPeakQSample(const V3D &position) const {
   // Create a peak from QSampleFrame
-  const auto goniometer = run().getGoniometer();
+
+  Geometry::Goniometer goniometer;
+
+  LogManager_const_sptr props = getLogs();
+  if (props->hasProperty("wavelength") || props->hasProperty("energy")) {
+    // Assume constant wavelenth
+    // Calculate Q lab from Q sample and wavelength
+    double wavelength;
+    if (props->hasProperty("energy")) {
+      wavelength = Kernel::UnitConversion::run(
+          "Energy", "Wavelength",
+          props->getPropertyValueAsType<double>("energy"), 0, 0, 0,
+          Kernel::DeltaEMode::Elastic, 0);
+    } else {
+      wavelength = props->getPropertyValueAsType<double>("wavelength");
+    }
+    goniometer.calcFromQSampleAndWavelength(position, wavelength);
+  } else {
+    goniometer = run().getGoniometer();
+  }
   // create a peak using the qLab frame
   auto peak = new Peak(getInstrument(), position, goniometer.getR());
   // Take the run number from this

Framework/Geometry/inc/MantidGeometry/Instrument/Goniometer.h

@@ -91,6 +91,10 @@ public:
   // Set rotation angle for an axis in the units the angle is set (default --
   // degrees)
   void setRotationAngle(size_t axisnumber, double value);
+  // Calculate goniometer for rotation around y-axis for constant wavelength
+  // from Q Sample
+  void calcFromQSampleAndWavelength(const Mantid::Kernel::V3D &Q,
+                                    double wavelength);
   // Get axis object
   const GoniometerAxis &getAxis(size_t axisnumber) const;
   // Get axis object

Framework/Geometry/src/Instrument/Goniometer.cpp

@@ -178,6 +178,38 @@ void Goniometer::setRotationAngle(size_t axisnumber, double value) {
   recalculateR();
 }
 
+/**Calculate goniometer for rotation around y-asix for constant wavelength from
+ * Q Sample
+ * @param Q :: Q Sample position in reciprocal space
+ * @param wavelength :: wavelength
+*/
+void Goniometer::calcFromQSampleAndWavelength(const Mantid::Kernel::V3D &Q,
+                                              double wavelength) {
+  double wv = 2.0 * M_PI / wavelength;
+  double norm_q2 = Q.norm2();
+  double theta = acos(1 - norm_q2 / (2 * wv * wv)); // [0, pi]
+  double phi = asin(-Q[1] / wv * sin(theta));       // [-pi/2, pi/2]
+  V3D Q_lab(-wv * sin(theta) * cos(phi), -wv * sin(theta) * sin(phi),
+            wv * (1 - cos(theta)));
+
+  // Solve to find rotation matrix, assuming only rotation around y-axis
+  // A * X = B
+  Matrix<double> A({Q[0], Q[2], Q[2], -Q[0]}, 2, 2);
+  A.Invert();
+  std::vector<double> B{Q_lab[0], Q_lab[2]};
+  std::vector<double> X = A * B;
+  double rot = atan2(X[1], X[0]);
+  g_log.information() << "Found goniometer rotation to be " << rot * 180 / M_PI
+                      << " degrees for Q sample = " << Q << "\n";
+
+  Matrix<double> goniometer(3, 3, true);
+  goniometer[0][0] = cos(rot);
+  goniometer[0][2] = sin(rot);
+  goniometer[2][0] = -sin(rot);
+  goniometer[2][2] = cos(rot);
+  setR(goniometer);
+}
+
 /// Get GoniometerAxis obfject using motor number
 /// @param axisnumber :: axis number (from 0)
 const GoniometerAxis &Goniometer::getAxis(size_t axisnumber) const {

Framework/Geometry/test/GoniometerTest.h

@@ -179,6 +179,56 @@ public:
         }
   }
 
+  void test_calcFromQSampleAndWavelength() {
+    Goniometer G;
+    double wavelength = 2 * M_PI; // k=1
+    DblMatrix R;
+    V3D Q;
+
+    // 0 degree rotation
+    Q = V3D(-1, 0, 1);
+    G.calcFromQSampleAndWavelength(Q, wavelength);
+    R = G.getR();
+    TS_ASSERT_DELTA(R[0][0], 1.0, 0.001);
+    TS_ASSERT_DELTA(R[0][1], 0.0, 0.001);
+    TS_ASSERT_DELTA(R[0][2], 0.0, 0.001);
+    TS_ASSERT_DELTA(R[1][0], 0.0, 0.001);
+    TS_ASSERT_DELTA(R[1][1], 1.0, 0.001);
+    TS_ASSERT_DELTA(R[1][2], 0.0, 0.001);
+    TS_ASSERT_DELTA(R[2][0], 0.0, 0.001);
+    TS_ASSERT_DELTA(R[2][1], 0.0, 0.001);
+    TS_ASSERT_DELTA(R[2][2], 1.0, 0.001);
+
+    // -90 degree rotation
+    Q = V3D(1, 0, 1);
+    G.calcFromQSampleAndWavelength(Q, wavelength);
+    R = G.getR();
+    TS_ASSERT_DELTA(R[0][0], 0.0, 0.001);
+    TS_ASSERT_DELTA(R[0][1], 0.0, 0.001);
+    TS_ASSERT_DELTA(R[0][2], -1.0, 0.001);
+    TS_ASSERT_DELTA(R[1][0], 0.0, 0.001);
+    TS_ASSERT_DELTA(R[1][1], 1.0, 0.001);
+    TS_ASSERT_DELTA(R[1][2], 0.0, 0.001);
+    TS_ASSERT_DELTA(R[2][0], 1.0, 0.001);
+    TS_ASSERT_DELTA(R[2][1], 0.0, 0.001);
+    TS_ASSERT_DELTA(R[2][2], 0.0, 0.001);
+
+    // 30 degree rotation
+    wavelength = 1.54;
+    Q = V3D(-0.63523489, -0.12302677, -0.29517982);
+    G.calcFromQSampleAndWavelength(Q, wavelength);
+    R = G.getR();
+    TS_ASSERT_DELTA(R[0][0], 0.866, 0.001);
+    TS_ASSERT_DELTA(R[0][1], 0.0, 0.001);
+    TS_ASSERT_DELTA(R[0][2], 0.5, 0.01);
+    TS_ASSERT_DELTA(R[1][0], 0.0, 0.001);
+    TS_ASSERT_DELTA(R[1][1], 1.0, 0.001);
+    TS_ASSERT_DELTA(R[1][2], 0.0, 0.001);
+    TS_ASSERT_DELTA(R[2][0], -0.5, 0.01);
+    TS_ASSERT_DELTA(R[2][1], 0.0, 0.001);
+    TS_ASSERT_DELTA(R[2][2], 0.866, 0.001);
+  }
+
   /** Save and load to NXS file */
   void test_nexus() {
     NexusTestHelper th(true);

Framework/MDAlgorithms/src/FindPeaksMD.cpp

@@ -4,6 +4,7 @@
 #include "MantidDataObjects/MDHistoWorkspace.h"
 #include "MantidDataObjects/PeaksWorkspace.h"
 #include "MantidGeometry/Crystal/EdgePixel.h"
+#include "MantidGeometry/Instrument/Goniometer.h"
 #include "MantidGeometry/Objects/InstrumentRayTracer.h"
 #include "MantidKernel/BoundedValidator.h"
 #include "MantidKernel/EnabledWhenProperty.h"
@@ -295,30 +296,9 @@ FindPeaksMD::createPeak(const Mantid::Kernel::V3D &Q, const double binCount,
     if (calcGoniometer) {
       // Calculate Q lab from Q sample and wavelength
       double wavelength = getProperty("Wavelength");
-      double wv = 2.0 * M_PI / wavelength;
-      double norm_q2 = Q.norm2();
-      double theta = acos(1 - norm_q2 / (2 * wv * wv));
-      double phi = asin(-Q[1] / wv * sin(theta));
-      V3D Q_lab(-wv * sin(theta) * cos(phi), -wv * sin(theta) * sin(phi),
-                wv * (1 - cos(theta)));
-
-      // Solve to find rotation matrix, assuming only rotation around y-axis
-      // A * X = B
-      Matrix<double> A({Q[0], Q[2], Q[2], -Q[0]}, 2, 2);
-      A.Invert();
-      std::vector<double> B{Q_lab[0], Q_lab[2]};
-      std::vector<double> X = A * B;
-      double rot = atan2(X[1], X[0]);
-      g_log.information() << "Found goniometer rotation to be "
-                          << rot * 180 / M_PI
-                          << " degrees for peak at Q sample = " << Q << "\n";
-
-      Matrix<double> goniometer(3, 3, true);
-      goniometer[0][0] = cos(rot);
-      goniometer[0][2] = sin(rot);
-      goniometer[2][0] = -sin(rot);
-      goniometer[2][2] = cos(rot);
-      p = boost::make_shared<Peak>(inst, Q, goniometer);
+      Geometry::Goniometer goniometer;
+      goniometer.calcFromQSampleAndWavelength(Q, wavelength);
+      p = boost::make_shared<Peak>(inst, Q, goniometer.getR());
 
     } else {
       p = boost::make_shared<Peak>(inst, Q, m_goniometer);

docs/source/algorithms/FindPeaksMD-v1.rst

@@ -85,6 +85,8 @@ First calculate the :math:`\textbf{Q}_{lab}` using
 
 .. math:: \phi = \sin^{-1}(-\textbf{Q}_{sample}^y \sin(\theta)/k)
 
+where :math:`\theta` is from 0 to :math:`\pi` and  :math:`\phi` is from :math:`-\pi/2` to :math:`\pi/2`. This means that it will assume your detector position is on the left of the beam even it it's not.
+
 Now you have :math:`\theta`, :math:`\phi` and k you can get :math:`\textbf{Q}_{lab}` using (1).
 
 We need to now solve :math:`G \textbf{Q}_{sample} =

docs/source/concepts/PeaksWorkspace.rst

@@ -49,6 +49,27 @@ Each Peak object contains a PeakShape. Only the integration algorithms which act
 Subtypes of PeakShape will then provide additional information. For example PeakShapeSpherical provides the radius as well as background inner, and background outer radius.
 
 
+Calculate Goniometer For Constant Wavelength
+--------------------------------------------
+
+If you set the `wavelength` (in Å) or `energy` (in meV) property on a
+PeaksWorkspace when the createPeak method is used the goniometer
+rotation with be calculated. This allows you to use one instrument
+definition for multiple goniometer rotations, for example adding peaks
+in Slice Viewer from multiple combined MD workspaces. It only works
+for a constant wavelength source and only for Q sample workspaces. It
+also assumes the goniometer rotation is around the y-axis only. For
+details on the calculation see "Calculate Goniometer For Constant
+Wavelength" at :ref:`FindPeaksMD <algm-FindPeaksMD>`.
+
+.. code-block:: python
+
+    pws = mtd['name_of_peaks_workspace']
+    pws.run().addProperty('wavelength', 1.54, True)
+    # or
+    pws.run().addProperty('energy', 34.48, True)
+
+
 Using PeaksWorkspaces in Python
 ---------------------------------