to control the rectification process. A system such as this can 
provide corrections for all sources of known error and, in addition, 
readily convert any type of geometry of the original exposure to 
an orthophoto condition. 
However these differential rectification techniques go one 
step too far for the purpose of selective rectification. Selective 
e rectification is the highly accurate rectification of an exposure 
correcting for all possible sources of error but retaining the 
correct displacement of the image due to relief. Further it can 
recreate any desired perspective geometry. Like the techniques 
of differential rectification proposed by Weibrecht(!) and Parenti(2) 
the selective rectification technique is made feasible by the 
giiliootioh of an analytical plotter. 
Selective rectification makes practical the preparation of a 
diapositive suitable for a stereoplotter regardless of the 
characteristics of the original photograph or the limitations 
eo e of the plotter. For example, it will permit photography with 
200 mm focal length afd 20° convergence to be transformed into 
a diapositive with zero degrees convergence and a principal dis- 
tance of 150 mm. In addition, this new diapositive will be 
corrected for all sources of systematic errors which are known. 
How can this be accomplished and what are its practical signifi- 
cances? 
A prime requirement is availability of an analytical plotter 
and its associated orthoprinter. As is commonly known, the