SUEDE DIURNO NN A
SET
This increasing significance of the human operator in the
photogrammetric process has led to a series of detailed studies of
observer capabilities on various types of visual tasks, in particular
pointing to circular targets, pointing to edges of image details, and
associated with these tasks, the interpretability of details. There
is a mass of data now available on these topics which must be correla-
ted, in order to apply the results to practical situations in photo-
grammetry. Selected papers will be referred to in studying the
following, three specific areas in this paper:-
(i) the assignment of appropriate variances to coordinate
observations as a function of the Modulation Transfer Function of the
photogrammetric system;
(ii) the systematic errors which occur when pointing is made
to edges or borders of photographic details;
(iii) the interpretability of objects as a function of the
characteristics of the imaging system.
2. Variances of Coordinate Observations
2.1 Data available on Pointing to Circular Targets
The data referred to in this section will be that given by
O'Connor (1967), Roger et al(1969) and Trinder(1971,1972,1973,1974).
O'Connor investigated the precisions achieved by an observer when
pointing to very sharp targets. His studies revealed that standard
deviations of repeated pointing observations as small as 1 sec of arc
(equivalent to 0.12um at an optical magnification of 10X) could be
achieved for very small high contrast targets.
Roger and Mikhail(1969) investigated the effect of non-homo-
geneous backgrounds on the subjective position of the target centre,
and also the relationship between pointing precisions in the x and y-
| directions. They found that standard deviations of y-coordinate
observations were greater than the standard deviations of x-coordinate
observations by a factor varying from 12% to 143%, with an overall
| average increase of approximately 30%. Based on their work it will
| therefore be assumed for this paper that y-coordinate standard
deviations are 1.3 times those of x-coordinates.
Published works of the author have dealt with point precisions
and systematic errors for sharp and blurred targets. The significant
pointing precisions were published in 1971 while derivations of the
relationship between the resulting observations and target and image
quality characteristics were published in 1973 and 1974.
Work on systematic errors (Trinder, 1972) demonstrated the
possible magnitude of such errors in pointing observations, and it was
shown that they may be much larger (up to 5 times) than the pointing
Standard deviation. Little is known on the extent to which systematic
