To GPS or Not to GPS?

[lacibaci]

Devices that report inaccurate GPS speed do it so because of a low sampling rate (usually once per second) which is fine for navigation and low speeds.
There are devices and dash cams (Waylens for example) that sample at 10Hz (ten times/sec) which will be a lot more accurate.

 

[SawMaster]

There are other factors involved too beyond sampling rate. Low-angle satellites, hills, and reflections have an effect which can't be easily compensated for if at all. And most dashcams use low sampling rates which give a lot of 'lag' so that in decelerating the display will show a higher speed than you're really going Even the most expensive GPS isn't always accurate although the better ones are usually close and that's usually close enough for most purposes. You just can't rely on their consistent absolute accuracy because it doesn't happen like that in the real world conditions we sometimes see. I don't want to be trying to explain this to a Cop, Judge, or Jury member- better to just not have it under discussion at all

Phil

 

[Deleted member 37895]

GPS is notoriously inaccurate for speeds which is why no rule-making body or record certification groups in the world will accept or affirm GPS speed readings. Only certified radar and measured time/distance readings are used where accuracy is paramount. Speed can be accurately extrapolated from the video and if done correctly is always certain and inarguable. For dashcam purposes location can be easily found by video alone. Someone will be investigating the scene so all that matters us that they arrive at the right place- seems that they always do even with no GPS involved. There is more than one numeric protocol (language) for GPS locations and they are not interchangeable, so if they're using another protocol your numbers can't be used by them- your info is then useless. Road names and distances are more universally understood and more generally used. Exact time is rarely relevant, and in a crash or road incident someone will be phoning it in within seconds so the call center will have that time logged. It's plenty close enough.

I can do everything needed without GPS, and with ample or better accuracy too. It's just one more thing which adds to costs and which can fail GPS has it's uses where it's a godsend but dashcams aren't on that list Use it if you wish to but know that it' not necessary at all.

Phil

GPS is accurate for speed within the precision limits of GPS. The distance you travel over 1 second is enough to calculate speed accurately with typical driving speeds.

But it doesn't really matter. If GPS is inadmissible in court to prove speeding, great, all the more reason to not worry about that.

Location is from GPS is simple and convenient. Figuring out location is not always easy, especially on rural highways. You don't need to worry about coordinate systems at all because whether law enforcement uses WGS 84 or NAD 83, the coordinates are identical, the only difference between those datums is vertical elevation. Even older datums like NAD27 are only off by a few meters, not enough to matter

 

[boilers]

don't break laws is the best course of action.

 

[Deleted member 46308]

GPS is notoriously inaccurate for speeds which is why no rule-making body or record certification groups in the world will accept or affirm GPS speed readings. Only certified radar and measured time/distance readings are used where accuracy is paramount. Speed can be accurately extrapolated from the video and if done correctly is always certain and inarguable. For dashcam purposes location can be easily found by video alone. Someone will be investigating the scene so all that matters us that they arrive at the right place- seems that they always do even with no GPS involved. There is more than one numeric protocol (language) for GPS locations and they are not interchangeable, so if they're using another protocol your numbers can't be used by them- your info is then useless. Road names and distances are more universally understood and more generally used. Exact time is rarely relevant, and in a crash or road incident someone will be phoning it in within seconds so the call center will have that time logged. It's plenty close enough.

I can do everything needed without GPS, and with ample or better accuracy too. It's just one more thing which adds to costs and which can fail GPS has it's uses where it's a godsend but dashcams aren't on that list Use it if you wish to but know that it' not necessary at all.

Phil

+1