Add wavelength parameter to WAND²

And make use of wavelength parameter in FindPeaksMD and PeaksWorkspace.

Framework/DataObjects/src/PeaksWorkspace.cpp

@@ -285,18 +285,20 @@ Peak *PeaksWorkspace::createPeakQSample(const V3D &position) const {
   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");
-    }
+  // See if we can get a wavelength/energy
+  // Then assume constant wavelenth
+  double wavelength(0);
+  if (props->hasProperty("wavelength")) {
+    wavelength = props->getPropertyValueAsType<double>("wavelength");
+  } else if (props->hasProperty("energy")) {
+    wavelength = Kernel::UnitConversion::run(
+        "Energy", "Wavelength", props->getPropertyValueAsType<double>("energy"),
+        0, 0, 0, Kernel::DeltaEMode::Elastic, 0);
+  } else if (getInstrument()->hasParameter("wavelength")) {
+    wavelength = getInstrument()->getNumberParameter("wavelength").at(0);
+  }
+
+  if (wavelength > 0) {
     goniometer.calcFromQSampleAndWavelength(position, wavelength);
     g_log.information() << "Found goniometer rotation to be "
                         << goniometer.getEulerAngles()[0]

Framework/MDAlgorithms/src/FindPeaksMD.cpp

@@ -197,7 +197,8 @@ void FindPeaksMD::init() {
   auto nonNegativeDbl = boost::make_shared<BoundedValidator<double>>();
   nonNegativeDbl->setLower(0);
   declareProperty("Wavelength", DBL_MAX, nonNegativeDbl,
-                  "Wavelength to use when calculating goniometer angle");
+                  "Wavelength to use when calculating goniometer angle. If not"
+                  "set will use the wavelength parameter on the instrument.");
 
   setPropertySettings("Wavelength",
                       make_unique<EnabledWhenProperty>(
@@ -296,6 +297,16 @@ FindPeaksMD::createPeak(const Mantid::Kernel::V3D &Q, const double binCount,
     if (calcGoniometer) {
       // Calculate Q lab from Q sample and wavelength
       double wavelength = getProperty("Wavelength");
+      if (wavelength == DBL_MAX) {
+        if (inst->hasParameter("wavelength")) {
+          wavelength = inst->getNumberParameter("wavelength").at(0);
+        } else {
+          throw std::runtime_error(
+              "Could not get wavelength, neither Wavelength algorithm property "
+              "set nor instrument wavelength parameter");
+        }
+      }
+
       Geometry::Goniometer goniometer;
       goniometer.calcFromQSampleAndWavelength(Q, wavelength);
       g_log.information() << "Found goniometer rotation to be "
@@ -757,11 +768,6 @@ std::map<std::string, std::string> FindPeaksMD::validateInputs() {
                                     "as the input.";
   }
 
-  double wavelength = getProperty("Wavelength");
-  if (getProperty("CalculateGoniometerForCW") && wavelength == DBL_MAX)
-    result["Wavelength"] =
-        "Must set wavelength when using CalculateGoniometerForCW option";
-
   return result;
 }
 

docs/source/concepts/PeaksWorkspace.rst

@@ -53,14 +53,15 @@ 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>`.
+PeaksWorkspace, or if the instrument on the PeaksWorkspace has the
+`wavelength` parameter, the goniometer rotation will be calculated
+when the createPeak method is used. 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
 

instrument/WAND_Parameters.xml

 <?xml version="1.0" encoding="UTF-8" ?>
 <parameter-file instrument="WAND" valid-from="2017-12-01 00:00:00">
   <component-link name="WAND">
+    <parameter name="wavelength" type="float">
+      <value val="1.488" />
+    </parameter>
     <parameter name="sample_logs_sum" type="string">
       <value val="duration" />
     </parameter>