Fig. 15 Actual Errors in Elevation Observed in the Center of Strip #5 
Bridged Using Horizon Photographs and Doppler Data. "Ssiid Line 
Shows Linear Adjustment a^irwd 
When auxiliary data is utilized, the absolute orientation in space 
of each stereo model is independent of other stereo models; consequently the 
propagation of errors is quite different and generally follows a linear function 
(Fig. 15). The double summation of errors does not take place; therefore, 
vertical control in the center of a strip has no real value. The closing errors 
before adjustment are considerably smaller than when the aero-polygon method is 
employed. However, there are, within a strip, undulations or local irregularities 
caused by inaccuracies in the auxiliary data and in the relative orientation. 
These are considered in the adjusting procedure if they are of a significant 
magnitude. 
The first step in the adjustment is to bring all independent stereo 
models to a common vertical datum. Here, the independent stereo models can be 
formed into strips coinciding with the flight lines, or into strips across flight 
lines formed of stereo models from adjacent flight lines, or into blocks. 
In our work in Nigeria and in Canada we combined independent stereo 
models of the same flight line into one strip and then combined the strips into 
one block. This is done mathematically by applying a vertical translation, so 
that the elevation of the center pass point in model n + 1 agrees with the 
elevation of the same pass point in model n. The discrepancies between models 
due to 03 influence are adjusted individually and then the closing error in the 
elevation, observed in the last stereo model of the strip (ground control model), 
is distributed linearly. Presently, we are investigating procedures for 
simultaneous adjustment of independent stereo models with electronic computers. 
The vertical block adjustment would be a relatively simple operation 
if it could be assumed that each strip is free from the influence of residual