PERSPECTIVE MEASUREMENTS
The combined effects of convergence and diminishing size
make it more difficult to establish and draw measurements in
linear perspective than in the other two drawing systems. But
there are techniques we can use to determine the relative
heights, widths, and depths of objects in the pictorial space
of a perspective drawing.
Measuring Height and Width
In linear perspective, any line in the picture
plane (PP) displays its true direction and true
length at the sca le of the picture pla ne. We
can therefore use any such line as a m
easuring
line (ML) to scale dimensions ina perspective
drawing. While a measuring line may have any
orientation in the picture plane, it typically is
vertica l or horizontal and used to measu re
true heig hts or widths. The ground line (GL) is
one example of a horizontal measuring line.
;
-..__ _
--- w
•..
A
-:--·---------------- ---~ --------+-- ->
...""..............
.........
f
~
/
/-~
/
Because parallel lines by definition rema in
equidistant but appea r toconverge as they
recede inperspective, we can use a pair of
parallel lines to t ransfer a vertica l or
horizonta l measurement into the depth of a
perspective.
·· .., _
__..., Once we establish a height or width, we can
- - - - ·,_ transfer the measurement horizontally or
vertically, as long as we make the shift
parallel to PP.
Digital Perspectives
Perspective measurements are not a major issue in 3D-modeling
programs because the software uses mathematical formulas to
process the three-dimensional data w have already entered.
e
PERSPECTIV EDRAWINGS / 115