20 
errors in CO . In this case, the discrepancies in elevations on the common pass 
points between the adjacent strips could be adjusted by fitting to an average 
datum. However, there is always some u; influence left in each strip. 
The information at our disposal for the strip and block adjustment 
is: 
1. closing error in elevation in the last stereo model of the strip, 
2. the difference in ^ and cu determined for the common photographs from two 
adjacent models, for photograph i, from model (i - 1, i) and model (i, i -h 1) , 
3. the differences in elevation on common pass points between adjacent strips, 
4. the reliability of auxiliary data, and 
5. the general "behaviour" of the strip during aerial triangulation. 
The discrepancies in elevation observed at the common pass points 
between adjacent strips are mainly due to the following causes: 
1. residual errors in U>> direction 
2. residual undulations of the strip in the direction or "datum" differences 
3. errors in stereoscopic reading of the elevations of the pass points 
4. errors due to transferring of pass points between flight lines. 
Separtion of these different errors is extremely difficult, if not impossible. 
The block adjustment was done graphically. This permitted a quick 
evaluation of differences between strips. A "cross-section profile" of the 
block, perpendicular to the direction of the strips, was plotted in terms of 
elevation differences between adjusted strips. 
2 
4 
I 3 
Fig. 16 
The "profiles" were plotted at intervals equivalent to the 
location of common pass points. These "profiles" are then interpreted and an 
appropriate adjustment is made. For example, a profile, as shown on Fig. 16, 
indicates that strip No. 2 is "out of datum". The proper adjustment will be as