Kölner Dom, Chor mit Obergaden, vor 1911
Anonymous (photo marked "Kgl. Meßbildanstalt", i.e. "Royal Prussian Photogrammetric Office")
Maximilian Hasak (1856-1934): Der Dom des heiligen Petrus zu Köln am Rhein. Berlin: Hermann Walther 1911, first table following p. 48. From the Internet Archive: <a rel="nofollow" class="external free" href="https://archive.org/details/derdomdesheilige00hasa">https://archive.org/details/derdomdesheilige00hasa</a>