upon the scale and the contour interval specified for the final map sheet. Table I is a typical
planning schedule used by a number of smaller companies as a planning guide in determining
the characteristics for the aerial photography. The particular table shown is predicated on the
use of 152 mm focal length, wide angle photography. The altitude is that above mean terrain.
Should the project be unusual in any respect, naturally this table would not be adhered to but it
would be necessary for a competent photogrammetric engineer to decide what variations would
and should be made.
TABLE I
FLIGHT PLANNING DATA
(Wide Angle - 152 mm f.1. lens)
Compilation Photo Flight Contour Ground* Ground*
Scale Scale Altitude Interval Coverage Coverage
(in feet) (in feet) (in feet) (in acres)
1:600 1:3000 1500 2 875 x 1750 33.8
1:960 1:4800 2400 2 1400 x 2800 88.2
1:1200 1:6000 3000 2 or 3 1750 x 3500 139.4
1:2400 1:12000 6000 5 3500 x 7000 558
1:4800 1:24000 12000 10 7000 x 14000 2240
1:6000 1:30000 15000 10 8750 x 17500 3494
* Area covered by stereo-model, assuming format of 3.5 inches by 7 inches at photo
scale.
The aerial photographic mission is planned very carefully to make maximum use of existing
recoverable ground survey points and also to recognize the road network in the area to make
access for subsequent ground control surveys as easy and economical as possible. The average
small company in its planning does not place any reliance on aerial triangulation because the
specialized equipment necessary is far too expensive andthe technical personnel and specialized
training required for this operation is not readily available.
The principal types of aerial photography used by private commercial firms in the United
States today are the 6-inch or 152 mm wide angle metrogon and 6-inch wide angle distortion
free type. The format of such photography is pretty well standardized at 9 x 9 inches. A small
amount of aerial photography with the 8-1/4 inch (210 mm) focal length with a 9 x 9 inch square
format is obtained and is used mainly for mapping in extremely mountainous or heavily forested
areas. Film cameras are used almost exclusively. À wide variety of aerial cameras are used
including not only all commercial makes now available but also a number of surplus U.S. Air
Force type mapping cameras.
The actual photogrammetric stereo plotting is done with glass diapositives. For those in-
struments which utilize the 9 x 9 inch format these diapositives are either printed by direct
contact with the negative, emulsion to emulsion, or emulsion of the diapositive to the base of
the aerial negative. In the latter case use is made of a parallel ray light source to eliminate
any error due to lack of contact between the film and the glass transparency and also to eliminate
error due to refraction through the film base. In the case where the diapositives are printed
emulsion to emulsion and then used in projection type anaglyphic instruments, it is necessary
of course for the instrument to have a correction for projection through the glass thickness of
the diapositive. Projection type diapositive printers are not too common among commercial
private organizations at this time. Of course they are essential for such organizations that use
the reduced format in their projection instruments. However, many of these organizations,
particularly the very small ones, rely on other companies which have the printer and sub-
contract to them the task of making the diapositives which they require. This is also true occa-
sionally with companies that require the printing of the nine inch square diapositives. Some of
the mapping companies which have purchased electronic dodging diapositive printers do dia-
positive ‘printing for their competitors. The use of electronic dodging for 1:1 printing of
