One of the regimental photographic units formed after 1865 in the French army to operate in the field. Led by a captain, the unit was equipped with cameras, darkroom facilities and surveying instruments. Its function was to take, process and print a series of photographs of the terrain that would assist surveyors in the production of strategic maps. Though the technology was still at an early stage, photography had potentially the advantage of promptness and accuracy, replacing the need for many instruments. While at this time advances were being made in the techniques and theory of photogrammetry and plane-table photogrammetric engineering, aerial photo reconnaissance methods with cameras carried on kites or balloons were already on trial.