Master
08-03-2007, 05:39 AM
Hey folks,
In light of a speeding ticket I had gotten a couple of weeks ago, it occurred to me that we should be setting up a forum where we can pool information about the various devices used by law enforcement, their limitations, and their operating requirements.
As I was (and still am) very much convinced that that officer in this case was mistaken about tagging me, I began to research operation of the machines used in law enforcement. This information will be used to disassemble his case against me in court. Some of the most interesting things that I found are:
1) unit must be pointed at a vehicle that is moving in a straight line toward the operator and the vehicle being surveyed must have a visible perpendicular surface
2) The operator must be supporting the targeting device either on a tripod or against the vehicle to ensure accuracy on target.
3) The operator should carefully note the conditions at the time of the targeting (distance, angle, viewplane, details of targeted vehicle) unless an add-on device that does this for the operator is connected to the system.
4) The angle at which the targeted vehicle is travelling with respect to the officer is critical. As the angle drifts from 180 degrees, the angle of incidence adds error ( refered to as cosine error) to the reading. Remember vector analysis from grade 10 physics? cosine is "X" component, sine is "Y" component. If you are at 180 degrees, sin180 = 0, cos180 = 1 therefore viewed velocity is 1 x noted speed and no correction is required. As you drift from 180 degrees, the error sets in.
5) The "Spread" of the LIDAR's beam at one kilometer is almost 3 metres. This means that an unsupported LIDAR pointed at two or more vehicles at a range of approximately one KM could be picking up a car in either of two lanes of traffic (even supported, this could be the case) and the device will return the faster speed, leaving the operator of the LIDAR unsure as to which vehicle he is targeting.
In my case, the officer did just about everything in the book wrong. If anyone is interested, I can tell the story, but that isn't the intent of this thread.
What I'd like to see are references and links to operators manuals. I'd like to hear stories about court cases that were won or lost and the legal details that were in play. This is something we can all use should we end up in court fighting a ticket. It could be a phenomenal resource.
Think of it like this: The police would have you think that LIDAR is a magical device that is both 100% accurate, 100% precise, and does not need to obey the laws of physics. None of this is true. LIDAR is a basic electromechanical device that has limitations and requires a specific set of guidelines to be followed for reliable results.
Ask a lab tech if they have to perform experiements with an electron microscope carefully, or if, becuase its a high-tech, million dollar device, and gomer could walk in and get good results with it. LIDAR is no different.
Anyone on board for this forum?
In light of a speeding ticket I had gotten a couple of weeks ago, it occurred to me that we should be setting up a forum where we can pool information about the various devices used by law enforcement, their limitations, and their operating requirements.
As I was (and still am) very much convinced that that officer in this case was mistaken about tagging me, I began to research operation of the machines used in law enforcement. This information will be used to disassemble his case against me in court. Some of the most interesting things that I found are:
1) unit must be pointed at a vehicle that is moving in a straight line toward the operator and the vehicle being surveyed must have a visible perpendicular surface
2) The operator must be supporting the targeting device either on a tripod or against the vehicle to ensure accuracy on target.
3) The operator should carefully note the conditions at the time of the targeting (distance, angle, viewplane, details of targeted vehicle) unless an add-on device that does this for the operator is connected to the system.
4) The angle at which the targeted vehicle is travelling with respect to the officer is critical. As the angle drifts from 180 degrees, the angle of incidence adds error ( refered to as cosine error) to the reading. Remember vector analysis from grade 10 physics? cosine is "X" component, sine is "Y" component. If you are at 180 degrees, sin180 = 0, cos180 = 1 therefore viewed velocity is 1 x noted speed and no correction is required. As you drift from 180 degrees, the error sets in.
5) The "Spread" of the LIDAR's beam at one kilometer is almost 3 metres. This means that an unsupported LIDAR pointed at two or more vehicles at a range of approximately one KM could be picking up a car in either of two lanes of traffic (even supported, this could be the case) and the device will return the faster speed, leaving the operator of the LIDAR unsure as to which vehicle he is targeting.
In my case, the officer did just about everything in the book wrong. If anyone is interested, I can tell the story, but that isn't the intent of this thread.
What I'd like to see are references and links to operators manuals. I'd like to hear stories about court cases that were won or lost and the legal details that were in play. This is something we can all use should we end up in court fighting a ticket. It could be a phenomenal resource.
Think of it like this: The police would have you think that LIDAR is a magical device that is both 100% accurate, 100% precise, and does not need to obey the laws of physics. None of this is true. LIDAR is a basic electromechanical device that has limitations and requires a specific set of guidelines to be followed for reliable results.
Ask a lab tech if they have to perform experiements with an electron microscope carefully, or if, becuase its a high-tech, million dollar device, and gomer could walk in and get good results with it. LIDAR is no different.
Anyone on board for this forum?