5. Fitting to ground control is included in stereoblock 
adjustment, Either the corresponding space coordinates are 
held rigidly to their known values or the conditions that 
they should approximate to these values are introduced as 
additional observation equations, 
At least some heights must be provided, either in the 
field or from adjacent stereoblocks, or else block will be 
unstable about the "hinges" between the strips, 
6, Solution of the normal equations, in about 80 variables, 
is just possible by Gauss elimination, passing data once only 
through store, A method of orthogonalisation in sections is 
described for inverting larger band matrices by holding only 
portions in store at a time, and requires no back solution, 
J.A. Weightman 
July 1960