DDAlign Manual

Abstract

Experimental setups in High Energy Physics are highly complex assemblies consisting of various detector devices typically called subdetectors. Contrary to the ideal world, where all these components are of perfect shape and at exact positions, existing devices have imperfections both in their shape and their relative and absolute positions. These are described by the alignment parameters.
To still measure the detector response from particle collisions with the highest possible precision, these imperfections are taken into account when converting measured signals to space-points in the measurement devices. This procedure is called detector alignment. $DD4hep$ does not want to solve the exact problem of the detector alignment itself, but rather support firstly algorithms determining the alignment parameters and secondly support the application which apply the measured alignment parameters and apply them to the ideal geometry for further event data processing.
We will present the tools to support the detector alignment procedures using the $DD4hep$ detector description toolkit. The DDAlign toolkit implements a modular and flexible approach to introduce and access the alignment parameters.
The design is strongly driven by easy of use; developers of detector descriptions and applications using them should provide minimal information and minimal specific code to achieve the desired result.