(405) 
is no need for long traverses to place points in specific locations. Coastal sur- 
veys require that every offshore rock and island be shown on the map. Without 
this camera many rocks would have to be located by ground triangulation at 
great expense and waste of the precious hours suitable for theodolite obser- 
vations in remote field operations. With it, however, these offshore rocks are 
an asset because they are used as passpoints along the offshore side of the first 
strip of photographs. 
Perhaps the greatest difference between nine-lens and single-lens plots is 
due to the great angular coverage which makes feasible the use of a 65 per cent 
endlap and a 55 per cent sidelap. With these overlaps the identity of the indivi- 
dual strips is not significant because the cross-azimuths are established as readily 
and accurately as those in line of flight and instead of a narrow band of com- 
mon points between strips, the entire area is imaged on at least two strips. The 
result is a rigid quadrilateral or block type plot with 6 to 9 radial lines inter- 
secting at each point instead of a series of coupled strips with only 3 to 6 inter- 
secting at a point. The rigidity of the plot is greater because only one-ninth as 
many photographs are required. 
The transparent vinyl-based radial line templets of the radial plot are used 
also for a graphic solution of the air camera tilt and flying height. The graphic 
solution has proven to be the most precise as all ground control points are 
utilized. Gross errors in the identification or location of control are eliminated 
and smaller errors are balanced out in the setting process. Rectification is done 
with a special camera which has tilting negative, positive and lens planes as 
well as scale adjustments. The rectified print has a residual tilt of less than three 
minutes of arc. The great angular coverage of the photographs also makes the 
“scaling” or graphic determination of the actual flying height correct within 
10 feet in 15,000. 
The Reading plotter is a special instrument designed to accomodate the 
36-inch square photographs. A pair of rectified prints can be oriented for 
stereo-mapping in about an hour. The nine-lens stereo model has the ground 
area coverage of 8 models of 6 inch metrogon photography with standard 
overlaps. The 65% endlap is used for gentle rolling terrain up to 2000 feet of 
elevation difference within the model. The greater overlap of photographs 
gives the operator a check by extrapolation on the leveling of each model and 
prevents him from unwittingly doing inferior work. 
The overlap is increased to as much as 75% for rugged mountain areas. 
The base-height ratio is 1.6 for an endlap of 65%. It is not necessary to use a 
base-height ratio of less than 1.1 even in the most precipitous terrain of Alaska. 
The wide angular coverage of the nine-lens photograph has proven to be ad- 
vantageous in rugged terrain because it “spans” entire mountain ranges to 
reach low valleys at many points in the individual models where single-lens 
photography would require several models to be set up on the steep mountain 
slopes with pass points in precarious positions. The large angular coverage also 
allows the photogrammetrist to span large bodies of water to locate offshore 
rocks and islands. 
The two Reading plotters that are now in production each produce 
1 : 20,000 scale topographic surveys at the rate of 6 square miles per day. 
This figure is based on the annual production records and includes all types