Instrument Access via SpectrumInfo, DetectorInfo, ComponentInfo¶

SpectrumInfo¶

SpectrumInfo can be obtained from a call to MatrixWorkspace::spectrumInfo(). The wrapper class holds a reference to a DetectorInfo object and calls through to this for access to information on masking, monitor flags etc.

DetectorInfo¶

DetectorInfo can be obtained from a call to ExperimentInfo::detectorInfo() (usually this method would be called on MatrixWorkspace). The wrapper class holds a reference to the parametrised instrument for retrieving the relevant information.

There is also a near-complete implementation of the “real” DetectorInfo class, in the Beamline namespace. The wrapper DetectorInfo class (which you get from ExperimentInfo::detectorInfo()) holds a reference to the real class. This does not affect the rollout, where the wrapper class should still be used in all cases.

ExperimentInfo now also provides a method mutableDetectorInfo() so that non-const access to the DetectorInfo is possible for purposes of writing detector related information such as positions or rotations.

ComponentInfo¶

ComponentInfo can be obtatined from a call to ExperimentInfo::componentInfo() (usually this method would be called on MatrixWorkspace). Much like DetectorInfo, the ComponentInfo yielded from this method call is a wrapper, which contains shape and index information, that cannot yet be moved in to the real Beamline::ComponentInfo. However, replacing existing usage of IComponent and IObjComponent wherever possible with ComponentInfo across the framework will represent a major step forwards.

For writing to the component tree. You can extract a non-const ComponentInfo via ExperimentInfo::mutableComponentInfo.

Basics¶

The conversion is similar to that for DetectorInfo, which is already largely complete in the framework. For ComponentInfo all instances of Instrument::getComponentByID(const ComponentID id) should be replaced using calls to the ComponentInfo object obtained from MatrixWorkspace::componentInfo(). The methods below can then be called on ComponentInfo instead of on the component.

• isDetector(componentIndex)
• detectorsInSubtree(componentIndex)
• componentsInSubtree(componentIndex)
• position(componentIndex)
• rotation(componentIndex)
• hasParent(componentIndex)
• parent(componentIndex)
• position(componentIndex)
• solidAngle(componentIndex)
• scaleFactor(componentIndex)
• sourcePosition()
• samplePosition()
• l1()

The following methods are useful helpers on ComponentInfo that allow the extraction of the component index for key components

• root()
• source()
• sample()

Indexing

The ComponentInfo object is accessed by an index going from 0 to the number of components (including the instrument iteself). The component index for a detector is EQUAL to the detector index, this is an important point to understand. In other words, a detector with a Detector Index of 5, for the purposes of working with a DetectorInfo and will have a Component Index of 5, when working with a ComponentInfo. Explained in yet another way: The first 0 - n components referenced in the ComponentInfo are detectors, where n is the total number of detectors. This guarantee can be leveraged to provide speedups, as some of the examples will show.

A ComponentID for compatiblity with older code, and be extracted from ComponentInfo::componentID(componentIndex), but such calls should be avoided where possible.

It is also possible to use the method componentInfo.indexOf(componentID) to get the index for a particular component ID. However, this is a call to a lookup in an unordered map, so is an expensive calculation which should be avoided where possible.

One should NEVER expose a Component Index or Detector Index through a user facing interface, such an algorithm or fit function.. Detector Index and Component Indexes are internal concepts for fast enumeration. It is however desirable to translate from a ComponentIndex via ComponentInfo::indexOf to as early as possible and in such a way to avoid repeated calls to this method, as stated above. Likewise, conversion back to a ComponentIndex, if so required, should be done as infrequently and, as late as possible.

Below is an example refactoring.

Before refactoring

auto instrument = ws->getInstrument();
std::vector<IComponent_const_sptr> children;
instrument->getChildren(children, true /*Get all sub-children too*/);
std::vector<IComponent_const_sptr>::const_iterator it;
for (it = children.begin(); it != children.end(); ++it) {
  if (const ObjComponent* obj = dynamic_cast<const ObjComponent*>(it->get())) {
    // Do something with the obj component
    obj.solidAngle(observer);
  }
}

After - looping over index

#include "MantidGeometry/Instrument/ComponentInfo.h"

...

const auto &componentInfo = ws->componentInfo();
for (size_t i = 0; i < componentInfo.size(); ++i) {
  componentInfo.solidAngle(i, observer);
}

Access to Components and working with Detectors¶

Detector Indices are the same as the corresponding Component Indices. Note that there are no dynamic casts. The following examples are for illustration purposes only.

Combining DetectorInfo and ComponentInfo

#include "MantidGeometry/Instrument/ComponentInfo.h"
#include "MantidGeometry/Instrument/DetectorInfo.h"

...

const auto &componentInfo = ws->componentInfo();
const auto &detectorInfo = ws->componentInfo();

std::vector<double> solidAnglesForDetectors(detectorInfo.size(), -1.0);
for (size_t i = 0; i < componentInfo.size(); ++i) {
  if(componentInfo.isDetector(i) && !detectorInfo.isMasked(i))
   solidAnglesForDetectors[i] = componentInfo.solidAngle(i, observer);
  }
}

ComponentInfo can give quick access to parent and sub-tree component and detector indices.

#include "MantidGeometry/Instrument/ComponentInfo.h"
#include "MantidGeometry/Instrument/DetectorInfo.h"

size_t bank0Index; // Component index for bank 0
...

const auto &componentInfo = ws->componentInfo();
auto bankComponents = componentInfo.componentsInSubtree(bank0Index);
auot bankDetectors = componentInfo.detectorsInSubtree(bank0Index);

Mutable ComponentInfo¶

The method ExperimentInfo::mutableComponentInfo() returns a non-const ComponentInfo object. This allows the methods below to be used.

• setPosition(const size_t index, const Kernel::V3D &position);
• setRotation(const size_t index, const Kernel::Quat &rotation);
• setScaleFactor(const size_t index, const Kernel::V3D &scaleFactor);

Useful Tips¶

• Creation of ComponentInfo is not cheap enough to perform uncessarily inside loops. For const access, ws.componentInfo() should be called outside of loops that enumerate over all components.
• If a ComponentInfo object is required for more than one workspace, include the workspace name in the variable name to avoid confusion.
• Get the ComponentInfo object as a const-ref and use const auto &componentInfo = ws->componentInfo();, do not get a non-const reference unless you really do need to modify the object, and ensure that the & is always included to prevent accidental copies.
• ComponentInfo is widely forward declared. Ensure that you import - #include "MantidGeometry/Instrument/ComponentInfo.h"
• As explained above, a detector index is the same thing as a component index. No translation necessary. The fact that the first 0-n component indexes are for detectors is a feature that can be leveraged.
• A bank always has a higher component index than any of its nested components. The root is the highest component index of all. This feature can be leveraged. Consider reverse iterating through component indexes when performing operations that involve higher-level components.