Appeal No. 98-1287
Application 08/359,706
the artisan, to arrive at the claimed subject matter, absent hindsight of appellants’ disclosure.
McClenahan discloses canceling “background noise” by subtracting the dark portion of a cycle from
the light portion of the cycle. However, the “background noise” identified in the reference consists of
reflected, as opposed to direct, light beams in the environment of wheel alignment systems. See the
statement of “Background of the Invention” in the reference, and particularly column 1, line 45 through
column 2, line 9.
In the prior art before us, there is nothing to suggest that unwanted (i.e., additional) reflections
of the light returning from a target were a problem in surveying instruments. Wells discloses that
surveying measurements may practically range from six up to 250 meters. (Column 5, lines 25-29.)
The reference also discloses that error measurements may occur due to
"atmospheric scintillations,” and teaches repeating the measurements to reduce the errors. (See column
10, lines 14-36.)
It thus appears that the normally occurring optical “noise” in a surveying system -- that is,
received light that is additional to the transmitted light -- is light from external sources, rather than from
extraneous reflections of the transmitted light. McClenahan discloses that filter 53 (Fig. 10) is provided
to minimize the effect of ambient light on sensor 29. See column 9, lines 2-6 of the reference. The
teaching of the reference that may be applicable to the use of survey
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