42 
Second photography of route 
Scale of the second photography is governed by the compilation scale of 
the planimetric maps and the &ccuracy required in profile and cross-section 
measurements. More details concerning this phase are given in the following 
discussions of compilation of planimetric maps and measurement of profile and 
cross sections by photogrammetric methods. Refer to second subsequent para- 
graph on this page. The photography scale is also governed by the relief 
height to flight height ratio, where applicable, and by the photogrammetric 
factors which are discussed subsequently. The types of photography usable are 
vertical and convergent. Principles applying in selection of the type to use 
are the same as presented in discussion of the direct procedure, except that 
after clearing is completed convergent photography may be used where otherwise 
it would not be practicable. 
Additional phases of procedure 
At this juncture of the indirect procedure, applicable phases of survey 
Work are accomplished which are comparable in detail and sequence to work done 
when the direct procedure is employed. These phases include horizontal and 
vertical control, plane coordinates, and compilation of maps, but exclude con- 
tours. There are, however, modifications and additions in procedure and in 
requirements because topographic maps are not used, and profile and cross sec- 
tions are measured in conjunction with or independent of planimetric mapping. 
Compilation of planimetric maps, and measurement of profile and 
cross sections by photogrammetric methods 
The materials and sizes of the planimetric map manuscripts and finished 
maps are the same as outlined in the discussion of direct procedure. Like- 
Wise, map manuscript scales are similar, except where they must be larger for 
photogrammetric measurement of profile and cross sections to required accura- 
cies, when they are measured at the time the maps are compiled. Finished map 
scales should be adequate for rights-of-way delineation, and for imposing the 
designed highway on the maps to serve as part of construction plans. 
The profile and cross sections are measured photogrammetrically on the 
stereoscopic models across the centerline or an offset baseline at an appro- 
priate stationing interval and at breaks in the slope of the ground. Measure- 
ments of profile and cross sections are governed by ruggedness of the topog- 
raphy, by minuteness in which the surface configurations of the ground is to 
be measured, by the accuracy required as listed in table 6, and by photogram- 
metric flight height factors. Such factors are the number of times the pho- 
tography flight height is greater than the desired average accuracy in measure- 
ment of spot elevations on profile and cross sections. Flight height factors 
of from 6,000 to 8,000 are utilized in optical train instruments, and from 
3,000 to 6,000 in double projection instruments. The profile and cross sec- 
tions are recorded, as convenient and desired on the maps, in profile and cross 
section notes, or for use in electronic computers, according to requirements, 
as punched cards, perforated paper tape, and magnetic tape.