t it will lead to the unification which is a most 
desirable feature and also it will lead to simpli- 
  
| | i 1 
A resolver. The resolver distributes the tracing 
I i ac signal to the X and Y transport servos in such 
| | [| ac a manner that the resulting motion of the car- 
AN VE i riage is tangential to the slope, i.e. along a 
M 8 d contour line. The X parallax signal is applied 
i |. sh to the other input of the steering resolver. The 
| | pe resolver distributes the X parallax signal in 
| i in such a manner that the resulting motion of the 
f i ra carriage is always perpendicular to, and di- 
i rected towards, the contour line, thereby main- 
E Of taining the pattern centre in contact with the 
| |. m terrain at the required height. As the pattern 
| ta centre traces out a contour, the slope analyzer 
| is constantly adjusts the angle of the steering- 
m : resolver shaft as required by the changing di- 
i Wi rection of slope. 
i pl 
I ca Plotting of Drainage 
i ac Stereomat can plot drainage automatically 
| fu by a modification of the contouring mode (Fig. 5) 
E di: For this purpose the tracing signal is applied to 
| > the Z servo in such a manner that the C.R.T. 
i SL assembly is driven slowly downward. Contact 
| sil with the model surface is maintained by a lateral 
i ca movement of the C.R.T. in response to the X 
i I parallax signal, as in contouring. It can be 
|. n shown that, under these conditions, the pattern 
6 of centre follows the paths of steepest descent, 
t be which are the drainage lines. 
| sti As in contouring, the plotting of drainage 
a ap is not completely automatic unless additional 
i I means are employed to ensure that no drainage 
i p paths have been missed. 
" lig 
N We Pattern Size 
i vil 
| The size of the scanning pattern is the 
t subject of conflicting requirements. On the one 
0 on hand, a small pattern is desired to resolve small 
i ty] topographic structures and to reduce “averaging” 
: errors on curved surfaces. On the other hand, 
t th a smaller pattern senses less image information 
" thus impairing the reliability of parallax de- 
a th: tection, and making the determination of slope 
i ce particularly difficult in flatter areas of the model. 
® lit For this reason, pattern size is not fixed but.is 
i : automatically adjusted in accordance with the 
|. tic nature of the terrain. 
À ba The T.S.M. signal from the correlation unit 
i de is used to control pattern size, as shown in 
Wu ev Figures 4 and 5. An increase in T.S.M. produces 
| je a decrease in pattern size. This reciprocal re- 
8 lationship between pattern size and terrain slope 
n no leads to a constant height difference across the 
" pattern with the following results: 
© rel Under flat conditions, where resolution 
# on and averaging errors are not significant, 
ji ic: the pattern expands facilitating slope 
if detection. Under conditions of severe 
| i of slope or rough terrain, where slope 
| 1 an detection is not a problem, the pattern 
" 
| en 
1 wi 
s Ori 
1 me 
4 DPI SS ap ea vin wiv UpPVIAQuual YWULR, 
AUTOMATIC STEREO 
contracts, satisfying the resolution re- 
quirement and minimizing “averaging” 
errors. 
Planimetric Plotting 
The plotting of planimetry is much more 
interpretive by nature than the plotting of topo- 
graphy and is therefore more difficult to automate. 
Stereomat assists in the plotting of planimetry 
by maintaining the pattern centre in accurate 
contact with the model surface, thereby relieving 
the operator of the necessity of making con- 
tinuous vertical adjustments as he traces out 
the features. In rough country, this assistance 
may reduce plotting time by perhaps 30 percent 
and is, therefore, a partial solution to the pro- 
blem. 
Ortho-Photography 
Ortho-photography is photography corrected 
for scale differences arising out of terrain re- 
lief, and camera angle at the moment of exposure. 
The resultant photo-map may be used as a sub- 
stitute for drawn planimetry for many purposes, 
and has both the advantage and disadvantage of 
retaining all of the planimetric detail available 
in the original photographs. In applications where 
the abridgement and delineation of drawn plani- 
metry are desirable, the photo-map may be used 
as the source material. The drafting of features 
may then be done with conventional drafting and 
tracing tools, thereby freeing the stereo-plotting 
instrument for automatic operations. 
Stereomat is expected to produce ortho- 
photography directly by means of a printing C. 
R.T. attached to the carriage. The action would 
be as follows: 
The amplified signal from one of the 
photo-cells is applied to the printing 
C.R.T. so as to modulate the light out- 
put. The deflection coils of the printing 
C.R.T. are excited by the scanning gener- 
ator so that the spot of light follows the 
same pattern as that on the main C.R.T. 
By this means an image of the terrain is 
produced on the face of the printing C. 
R.T. and a lens system projects this 
on to a sheet of sensitive paper. Expos- 
ing the sheet, while profiling the model, 
gives the scale correction required for 
ortho-photography. 
A non-projection Stereomat will probably 
be required for printing photo-maps because of 
the quantum noise limitation of Stereomat on a 
projection plotter. 
Triangulation 
A triangulation Stereomat would have pro- 
IUUTIU, UTIACI. CTUUU TTUATUMTILU/ UJ TVIT I1CIUVU, Dui no 
adequate record of the discussion is available 
for publication. 
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