The observation equations for least squares strip 
adjustment are derived from (2) as 
Suey, 01m DU SANG 0E9, Hg) - PQUO(N, ES H2) 
gy (Oy, UD = BU) (Nq, Eq, Hq) - pn (N,, E,, H,) 
Block adjustment is formulated in an analogue manner. 
Here, difference equations should also be formulated 
between the last photograph of one strip and the first 
photograph of the next strip. 
Final Remarks 
The adjustment is far more robust to blunders or gross 
errors, as they will not be partly absorbed by the 
estimated coefficients for the systematic correction 
terms. Also, proper accuracies are obtained for the minor 
control points after block adjustment, unperturbed by the 
assumption for systematic errors, and ground control 
requirements can be clearly understood, avoiding potential 
hidden singularities as in block adjustments with 
additional parameters (Kubik, 1988). 
Differential photogrammetry teaches us, that in the 
presence of systematic errors, denser ground control is 
required as proposed so far; full model control should be 
repeated at regular intervals in order to stabilise the 
accuracy in the block. Detailed accuracy studies for 
differential photogrammetry will be published by the 
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