Speaker
Description
Since the mid-1980s, LGC (Logiciel Général de Compensation) has been CERN’s primary software for the least-squares adjustment of survey networks and alignment processes. Historically operated as a self-contained executable, it has evolved into an adjustment engine embedded within a diverse range of survey workflows. The evolution was driven by both operational needs and a deliberate strategy to open LGC beyond its original context. This strategy involved exposing the computation core as a reusable library, developing machine-readable outputs, documenting stable interfaces, and encouraging external applications. Documentation improvements and active community outreach have been integral to this effort. On the technical side, two developments stand out: a JSON serialisation format and an application programming interface (API), which together expose LGC as a callable library and provide structured access to its results.
This paper presents several domains in which LGC is now used programmatically: field acquisition, graphical survey environments, live monitoring systems, post-processing scripts, and simulation. All were built outside LGC’s C++ codebase. Where a given integration required additions to LGC itself, those were made generally available to all users. The JSON serialisation format has further given rise to standalone tools such as dynamic result reports and geographic visualisation interfaces. Some were contributed by people without any surveying or software development background, illustrating that neither use nor contribution requires deep knowledge of LGC’s internals. With LGC publicly available under an open-source licence since early 2026, these examples document CERN’s current practice and invite the broader community — surveyors, scientists, and developers alike – to use, adapt, and extent the LGC toolbox.
