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5 of the S ereomicrometer O.G. de V eloped b Engineer Santoni and construc ced b V the firm Gal ileo, 1n Flor ence, Ital
REPORT OF COMMISSION VII 97
micrometer, E, is mounted in its place. The stereomicrometer consists essentially
of a first carriage, a, which is guided in its movement in a Y direction by the
groove or central guide, A, and of a second carriage, b, which can move in an
X direction guided by two wheels mounted on the carriage, a. The stereomi-
crometer is in this way movable according to a system of guides of an orthogonal
cross.
The principle characteristics of this instrument are: 1. complete utilization
of a stereogram with only one adjustment, using photos as large as 30 X 30 cm;
2. interchangeability, in a period of 30 seconds, between the normal observation
stereoscope and the stereomicrometer; 3. a device permitting rapid reciprocal
orientation of the photographs; 4. a stereomicrometer offering the remarkable
enlargement of X3 and endowed with great variation of distance between float-
ing marks (80 mm). For distances up to 40 mm it is possible to measure with a
precision of 0.01 mm; 5. ample adjustment of the stereomicrometer with cross-
guides, which permit the instrument to be connected to a direct tracer or to a
pantograph; 6. a reducer-enlarger pantograph; and 7. a case to contain the
board, orientation apparatus, stereomicrometer and pantograph.
Additional types of equipment which frequently prove useful to the photo
interpreter include the following: 1. graphs of sun's azimuth at various times of
the day and year from which photographs can be oriented through study of
their shadows; 2. photo coverage graphs indicating both longitudinal and lateral
coverage of various cameras at various altitudes and indicating the photographic
scale along the normal to the principal line; 3. graphs for determining the angle
of inclination on oblique photographs showing the apparent horizon; 4. “Telley
fans" for transferring onto topographic maps the directions obtained from azi-
muthally gridded photographs. A ratiograph (spiral logarithmic graph) for the
cransformation of scale is now in the process of preparation.
PHOTOGRAPHIC FILMS, FILTERS AND SCALES SUITABLE FOR PHOTO INTERPRETATION.
Simultaneous panchromatic and infrared aerial photography at times proves
very useful to the photo interpreter particularly when attempting to detect
and identify camouflaged installations, or to make vegetation interpretations in
mixed hardwood-conifer stands. Except in unusual circumstances, however, i
a choice must be made between panchromatic and infrared aerial photography
the former is preferred.
Photographic scales are conveniently classed as follows: 1. small scale pho-
tography is 1/16.000 or smaller; 2. medium scale photography is 1/10.000 to
1/16.000; and 3. large scale photography is 1/10.000 or larger. In general it can
be said with reference to scale that in order to identify some feature having
actual (ground) dimensions of 1 X 1 meter, it is necessary that its image on the
photographs should have the dimensions of 0.25 X 0.25 mm. This relation
obviously will vary with many factors including conditions of exposure, type
of film and filter, resolution, etc. For overall terrain appreciation small scale
photography is preferred to large scale photography since the former permits
the stereoscopic study of a much larger area in a single stereo model. It is
obvious, however, that when one wishes to make accurate measurements of
short ground distances or to observe small details, large scale photography 1s
necessary.
