According to the article on page 17/406, after the Ananta Samakhom Throne Hall’s construction was finished, the grand ceremony began.
In that regard, King Rama VI ordered a full decoration along Ratchadamnern Klang Road from Pan Fa Leelad Bridge to the royal courtyard in front of Dusit Palace, where the Equestrian Statue of King Rama V was, later on, erected, with Japanese lanterns, electrical lanterns also flanked with rows of national flags (white elephant, back then) along the way.
This computer colored photo shows the golden pavilion which was a place where the King after arriving at the site used to change his official costume to the traditional costume to join the ceremony which was Brahman ritual.