If you have to do this again at any point, you will likely find more success if you attack the accuracy of the speed measuring equipment, and specifically any traceable calibration of that equipment. Calling into question the accuracy of the GPS location fix in the photo did not directly say anything about the speed measuring device. This is because the speed measurement device was very likely not the GPS locator unit that stamped the photo. The speed measuring device was likely an independent radar or laser unit. The prosecution should bring with them proof that the unit had been field tested that day to verify correct functioning andd field accuracy, and as well should bring the calibration evidence showing professional calibration of the speed measurement device. But unless you question the speed measurement device itself, they have no reason to say much about the calibration status of the device. And since most defendants argue simply "I wasn't speeding" the prosecutors sometimes get lazy and leave the calibration documentation behind. If you question the calibration and they don't have the requisite evidence, then you've got something you can use to convince the judge to rule in your favor.