We have performed a simple experiment to estimate the error of both
the panning motor and the
45 *degrees* mirror. It consists of taking
4 measurements in a large room as follows.

- 1.
- Place the rangefinder in the approximate center of the room.
- 2.
- Aim the laser horizontally at the center of one wall, and mark
its position (called
*A*). - 3.
- Rotate the mirror
180
*degrees*vertically, and mark its position on the opposite wall (called*B*). - 4.
- Rotate the panning unit
180
*degrees*horizontally, repeating the above markings (called*C*and*D*).

The measurement results are shown (exaggerated for effect) in figure
8. The calibration result will define values for *x*and *y*, and are determined as follows.

If the mirror is at
45 *degrees*, then *x* will be
180 *degrees*. The
value of *x* is determined by
.
This
yields
*x* = 179.54 *degrees*. Thus the angle between the cone
and the plane is
(180 - *x*)/2 since the error is equal on
both sides of the cone. It is
.
Knowing
this value, we can recalculate the actual position of the laser.

The rotation of the panning motor is captured by the value for *y*.
It is computed by
,
since
is
covered twice (note the rotation arrow in figure 8).
This error is assumed to be linearly distributed over the
span of the panning motor and is large enough that
compensation is required. Fortunately, the compensation involves
changing a single constant, the ratio of positions per degree, thus
the correction is trivial.