The years 1954-59 are defined by Van Hoeydonck's dedication to geometrical painting. Initially inspired by the rooftops of Fez and the harbour lights of Saint-Tropez, Van Hoeydonck developed his purely geometrical paintings from a concretely constructed abstraction of reality. His geometrical works were exhibited at one-man shows at the Galerij Accent in Antwerp (1957) and at the Galerie Saint-Laurent, Brussels (1959). In his preface to the 1959 catalogue, Michel Seuphor summed up the essence of Van Hoeydonck's artistic development with the words: 'Il n'y a pas de plus belle tache que de construire. Il n'y en a pas qui soit plus digne de l'homme, plus proche de la profonde nature de l'homme'. In 1990 Whitford Fine Art dedicated a comprehensive publication to accompany an exhibition of the geometrical works of Van Hoeydonck dating the years 1955-1959.

Van Hoeydonck's works are held by museums worldwide including: Galleria Comunale d'Arte Moderna, Rome; Israel Museum, Jerusalem; Museum of Modern Art, New York; The Solomon R. Guggenheim Museum, New York; Smithsonian Institute, Washington DC; Van Abbemuseum, Eindhoven; Museum Boymans-Van Beuningen, Rotterdam; Walraff-Richartz Museum, Cologne; Koninklijk Museum voor Schone Kunsten, Antwerp; Mu.ZEE, Oostende.