photographs, the accented co-ordinates are obtained from the 
measured co-ordinates with the help of (1) and the space 
co-ordinates are calculated from 
LA S > 
yr “a 
X c Y xf 
and Z from either ---- (2) 
- 2 
Zz: 1.3 
or 
Z = 
/ 
Yos x5. > 
which gives a useful check”, 
Lens distortion values were applied to all measures, Five 
independent check points were observed, in addition to the four 
control points. Each point gave & residual error in X enc Y and 
two in Z (equations (2)) and the standard deviation from the 20 
residuals was 3 15mm, 
Above the base of the cupola there are eight raised panels 
and ribs which correspond to the sides and corners of an 
octagonal drum, The dome therefore comprises portions of four 
cylinders which intersect in pairs of ellipses and it is these 
which provide the profile, when viewed against the sky, of 
approximately elliptical ribs. The mean radius of each cylinder 
to the surface of the lead covering was 14.16 feet Ÿ 0,02 feet 
(4,32m * 6mm), Fig.3 shows the reconstruction by Mr,Trenwith 
Wills, based on the photogrammetric result, where 14 feet 
2 inches (t3 inch) has been employed as the critical dimension, 
The original supporting frame may well have haó & radius of 
14 feet, The reconstructed dome, with gilded lantern and finial, 
may be seen in Fig,4; the photograph was taken in 1962 from the 
south west camera station of the original 1924 photography. 
DIMENSIONS OF THE CEILING 
Unfortunately, the 1924 group of photographs did not contain 
a view of the Pellegrini fresco taken with a vertical camera axis, 
Fig.5 shows an oblioue viewfrom the Henson photography which was 
used in conjunction with a vertical picture taken in 1909, the 
original of which did not exist, It was necessary to rephotograph 
a half-tone illustration in Country Life, However, the problem of 
deriving dimensions for the ceiling was wes not so complicated nor 
was the required accuracy so great as for the exterior of the 
dome, Certain reasonable assumptions were made about the geometry 
of the pictures and the construction of the hall below the dome, 
The result of a further application of projective transformation 
(equation (1)) was a ceiling of spherical section, 18 feet 
(5,49m) in radius and with a rise above cornice level of 6 feet 
(1.83m). Fig.6 shows & section of the ceiling with the photo- 
grammetrically determined points approximating & circular curve 
of these dimensions, Points derived from Vitruvius Britannicus 
dià not agree with the photogrammetric findings. 
Mr,Scott Medd repainted the Pellegrini fresco in 1962, 
  
34