Thursday, July 16, 2015

The Lidar Lie

After Baltimore City's disastrous speed camera program was forced to admit that their supposedly perfectly calibrated equipment had produced erroneous speed camera tickets due to what speed camera contractor Xerox referred to as "radar effects", speed camera using agencies desperately needed to find a new narrative to replace the platitude "if you won't speed you won't get a ticket".

One of the claims now made is that even though there were problems with speed cameras in Baltimore, that other speed cameras which measure speed with LIDAR cannot be wrong.  The implication that the device uses laayyyzeerrrs, which sound spacey and high tech, is supposed to lead one to believe the device cannot be wrong.

Because anything with lasers on it sounds cool
Of course, this is not true. It has been known for years that even devices which are properly calibrated can still be wrong due to external phenomenon.  One example of this is the sweep effect, something which has been known to exist and documented for years.

You see, in order for a hand held LIDAR device to work accurately, the beam must be held on a single point on the object being measured by the officer.  With a speed camera, the device tracks that point "automatically".  The assumption is that the machine does this correctly, and that it does this correctly every single time, in every single scenario, regardless of circumstances or external conditions, and that the beam will never end up "sweeping" from one point on the target to another which is a different distance away without this being detected.  Just like everyone assumed a radar device could not be wrong merely because it passed an internal calibration, and nothing outside the device could cause an error.... even though that turned out not to be true.

Certainly if you go to court, whomever represents the state will not acknowledge any knowledge of such phenomenon, even though they do have such knowledge, because testilying is a thing.  Rest assured the district court will always assume a device can never be wrong unless there is some very compelling evidence that it was wrong in your specific case... since in Maryland the concept of "reasonable doubt" is a privilege which applies only to career criminals, and not to ordinary citizens like YOU.