4 
by the National Research Council of Canada. The stereo 
mate, which is described in more detail later in this 
paper, involves the displacement of elemental image areas 
from their orthographic positions, in the positive X- 
direction only, as a function of elevation above some 
reference datum. Thus, false parallaxes are introduced 
in the new stereomate photograph and, when viewed with 
the orthophoto stereoscopically, a model is seen that has 
no Y-parallax and is absolutely oriented in terms of 
spatial content. The model is easy to view and can be 
exploited to generate various cartographic products with 
relatively simple instrumentation. 
A third special case of image transformation 
has been accomplished on the printer - this involves 
changes in perspective. In a process similar to recti 
fication, but essentially a reverse process, a vertical 
photo can be converted to an oblique view (Figure 15) . 
SYSTEM DESCRIPTION 
The Off-Line Orthophoto Printer is referred to as 
a universal printer. It can provide the above transfor 
mations from any focal length input - both frame and 
panoramic - that can be geometrically defined. Figure 
2 depicts a block diagram of the system showing the 
separation of the optical-mechanical unit and the control 
system. 
The printer provides for projection, transfer, 
and recording of the input image, plus manual viewing 
for orientation. The projector images the filament 
of the lamp to the photo plane at a line width of approxi 
mately 50 microns, and several millimeters in length. 
The orientation of the filament is in the local model 
X-direction of the input imagery. The rotation is also 
linked mechanically to the dove prism in the transfer 
optics so that as the filament is rotated, the dove 
prism is counter-rotated to align t;he output image element 
in the model X-direction, which is the X-axis of the 
film drum. Just above the film drum is a mechanical 
mask, of variable width, which determines the length 
of the line element to be exposed upon the film. This 
mask permits a choice of 1, 2, 3 and 4mm profile widths. 
The above projection and image transfer technique 
eliminates the problem of discontinuities of image boun 
daries between profiles, due to changes in terrain 
elevation that can occur across the width of the profile 
and between profiles.