You will need to satisfy the court as to the accuracy of your GPS with respect to tracking location and speed. There are few companies that will test and certify an over the counter or vehicle GPS to do this and as Mr. K pointed out, it will be expensive for you to do so and have their technician testify on your behalf. OTOH, because LIDAR results are used in court routinely, the units are tested and certified periodically and the courts routinely accept calibration certificates alone to that effect.
Should you wish to challenge the findings of the technician who calibrated the LIDAR device in question, prior to trial you will need to seek discovery, obtain a copy of the curent LIDAR certificate, identify the technician and subpoena him to testify. I would use caution in doing this. Unless you are well versed in LIDAR devices, you will not know the correct questions to ask and it will appear you are doing this simply to prolong the trial and be a PITA because you are pissed that you got a ticket. Courts to not take kindly to such tactics.
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