18 
possible to compute the flying height above the same vertical datum for each 
vertical aerial photograph of the same strip. We know then the following 
elements of absolute orientation for each stereo model within each strip: 
(1) tip and tilt determined from the horizon camera 
(2) flying height relative to a vertical datum 
(3) the base distance between each exposure given by Doppler data, and 
consequently the scale. 
The slope of the barometric surface can be determined either from 
formula 3, or by having a known ground elevation at the end of the flight line 
and comparing the computed flying height with the one determined from the ground 
control (Fig. 14). 
The above information permits plotting any model within a strip at 
a correct scale and a correct vertical datum without the necessity of bridging 
the entire strip in a stereo-plotting instrument. Independent stereo models of 
many strips can be combined into one block which can then be adjusted. 
It can easily be seen that the accuracy of transferring the vertical 
datum from the camera stations to the terrain by the above method depends largely 
on the accuracy of the base distance (scale), or the accurate knowledge of the 
terrain clearance. The accurate scale can be determined either from a horizontal 
block adjustment prior to the vertical adjustment, or directly from .an Airborne 
Profile Recorder, provided the terrain is not covered with heavy vegetation and 
is relatively flat. 
5. ADJUSTMENT OF AERIAL TRIANGULATION 
The adjustment of strips when auxiliary data is introduced in the 
aerial triangulation procedure must be approached differently from that of the 
aero-polygon method. When the latter method is used, the adjusting procedure 
revolves around elimination of large errors in elevation caused by a double 
summation of accidental and systematic errors, and also by the influence of the 
earth's curvature. This is usually accomplished by means of second- and third- 
order functions. The variations from this ideal function of errors are not taken 
into account, although they undoubtedly exist.