4 Local Alignment
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Generally such a behavior can be achieved in two ways. The usage strongly depends on the use-case required by the client:
- either the ideal geometry in memory is changed directly to reflect the measured geometry. This approach has the disadvantage, that all measurement points on a daughter volume can only be transformed to the global coordinate system using one single transformation. Time-dependent changes of these transformations cannot be modeled. Hence, for multi-threaded systems this approach is of limited use. However, this is the perfect approach to simulate distorted geometries. This approach is naturally supported by the ROOT geometry toolkit.
- The second possibility is to not modify the ideal geometry in memory, but to provide instead transformations to move measured coordinates to their correct place in space. This approach allows to keep several - also time-dependent - transformations in memory. Ideal to support multi-threaded data processing frameworks, which become more and more popular.
DDAlign supports both possibilities as will be described in the following sections.