-11- 
n—1 
51 mk Y k+i- Y k 
m «= —being mk = 
n—1 P k+1 P k 
The rectangular axes which had been roughly defined along 
the segment Sp Sp could now be constructed within the needed accuracy 
of 0.2 mm. 
The grid itself was constructed with the beam compass and 
a stretched thread used. A primary net of 50 cms was laid, and then 
the final 25 cms grid was plotted. 
5.4 - Assembly 
On account of the great length of the zone, the radial 
triangulation had to be broken down into four sections. As the pro 
jection system was the U.T.M. (l866 Clarke elypsoid) one of the cum- 
pulsory breaks was along the dividing meridian 36 Q East -Figure n 5 «4« 
In order to reduce distortion of the base to a minimum, 
the grid far,, each section was constructed just before assembling. 
As mentioned before, approximately 9% of the control points 
were discarded in this phase, considering the contradictions they im 
plied, On the whole a few badly made templets were easily detected 
and replaced. 
In order to ensure a smooth linkage of the different sec 
tions, 4 to 6 templets were always overlapped. Besides, as the brea 
king zones could not always be chosen in accordance with the ground 
control distribution, the auxiliary points of the radial triangulation 
situated in the middle of tho overlapping sections were suitably trans_ 
ferred to the following grid. For that a transparent vinylite sheet, 
,01 M thick, was used. 
These sheets are normally used for small scale plotting, 
alternating with aluminium laminated paper. 
6,- CONTROL FOR THE RECTIFICATION AT l/lO.OOO 
Due to the 1/20,000 scale of the radial triangulation, 
the following procedure was adopted, 
6.1 - Transfer of the radial triangulation control 
All the slotted templet points were pinned, strip by 
strip, on transparent bands 9,5" wide, after aligning the strip and 
band axes. Being the most stable transparent material available, 
.01” vinylite was first used. Because of its reduced size - 37" x 
35 n ~ end the limited time, it was decided to use permatrace obtai 
nable in rolls up to 20 meters, 
6.2 - Control Grid 
For each of the permatrace bands containing the radial 
triangulation control, a double size band was cut. Along the whole