SO0 THREE-DIMENSIONAL PHOTOGRAPHY
be placed in perspective without overlapping the first. For a draw-
ing to be viewed in the normal stereoscope, it is advisable that the
first plan should be kept to a size of two inches or less and that the
station point be moved 21/4 inches. In practice this usually means
that the drawing will be made in a size sufficiently large to permit
easy drawing and then the completed stereo pair reduced to
correct size by photography.
When the dual plan is transferred to the second sheet and the
two perspective drawings made, they will automatically be in
stereo relief. It is understood that, although the station point is
moved, the vanishing points must remain the same for both
drawings.
Geometric Freehand Lattice.-For reproducing a freehand
drawing it will be necessary to draw a geometric lattice (using the
preceding technique). This lattice surrounds the drawing like a
cage. Significant points in the drawing are given points in space
within this cage. Then the second cage is drawn in stereo relation-
ship and the corresponding (homologous) points are produced.
These points permit the correct stereo orientation of the second
freehand drawing.
Freehand Net.-The freehand net is a type of graph paper in
which there occur vertical lines at intervals, usually of one centi-
meter. At a distance of one millimeter on each side of each line
are drawn broken lines, and spaced i.5mm from the outer sides of
the broken lines there are dotted lines.
The solid lines represent mid-distance, the other lines represent
varying distances from infinity to near foreground. One freehand
drawing (on tracing paper) is placed over the net. A corre-
sponding drawing is made over the other side of the net and the
significant points moved to one side or the other according to the
distance of the point. For example, the nose is placed upon a
solid line, a similar nose outline is drawn upon a dotted line
which is nearer the first drawing. The first drawing is moved so
that a distant hilltop is coincident with a solid line. In the oppo-
site drawing, for example the right one, the second hilltop is
drawn coincident with the dotted line which is adjacent to and at
the left of the homologous solid line. Thus the drawings are
shifted back and forth to locate various parts of the drawing. It is