This funicular model was reconstructed at the University of Stuttgart based on the few vestiges of the original, photographs and descriptive accounts and is now preserved in the basilica museum. The reflection in the mirror above shows how the finished structure will look (only partially visible).

The technique Gaudí used to design the Church of Colònia Güell was to hang little bags of birdshot from strings. Gravity would pull these bags downwards, giving even weight distribution and stretching the strings to form a model structure, thus showing him the shapes and angles his pillars would need to be. By photographing the model, then inverting the photograph, Gaudí could then see the model as it should look. (Wikipedia) He demonstrated that the model of weights and strings he constructed for the project for the church at Colonia Güell was [an] indispensable previous experiment for the new structural conception of the project for La Sagrada Família. (Sagrada Familia site)

This is the church for which it was designed: