What's your reason for GPS?

[Milamber]

First off, this post doesn't imply that I disagree with using GPS to display speed and location, in fact it can be very beneficial.

Given the small amount of pressure that is needed from ones "boot" the posted speed limit can often be breached without much effort. Does this concern anyone, in the event law enforcement needed to use footage as evidence?

Driver safety is everyone's responsibility at the end of the day, unfortunately it's very easily to be scrutinized.

 

[Street Guardian USA]

http://dashcamtalk.com/forum/threads/is-having-gps-on-the-dash-cam-important.2616/

 

[Quick]

I have a use for GPS (selective) but none of the dashcams provide gps that is adequate.
I also use my dashcam for road racing at the track. While driving on the street (actually all the time) I leave the dashcam gps turned off -- does not save to the log or video. On the track I need 5 to 10 hz. I use an external, dedicated GPS receiver with data logged (bluetooth) to a smart phone app.

 

[jokiin]

Some of them do 5hz, most that are using these 5hz models run them at 1hz anyway

 

[Jet Lag]

Primary reason is to have accurate time (from satellite) which will be location dependent. I live in France but travel frequently to UK so do not want to physically change the time on the camera for each trip. Time in UK is 1 hour behind France!


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[size_t]

I have the GPS turned on for a few reasons:
- I get lost a lot, semi-intentionally, and seeing the map of my trip is much easier than having to watch the video & map it out on google maps myself. ( and for a larger example, I recently travelled 1200 miles only loosely following directions. If I want to know the exact route I took, all I have to do is glance at the image regstratorviewer generates, without it I'd have to guess / watch hours & hours of video..)
- I like seeing my speed, and would definitely want to know what it was should an accident occur. Without trying to start any arguments, my goal in having the camera is fairness. If I were to get into an accident where having video without my speed would show it to be 100% other persons fault, or having video + my speed would make be a shared blame, I would definitely want to share the blame.
- Third point references back to ^, knowing my speed is recorded makes me stick closer to the speed limit! Dampening that ever present temptation to speed is certainly a benefit

 

[jokiin]

knowing my speed is recorded makes me stick closer to the speed limit! Dampening that ever present temptation to speed is certainly a benefit

that is definitely a trend that has been noticed

 

[kuoh]

I'm not aware of any "cheap" consumer level GPS units that have to ability to auto adjust GMT offset based on current location. All the ones I've seen receive UTC from the satellites, then adjust the displayed time based on the offset input by the user. So if you set the GPS to French time and travel to the UK, the GPS does not automatically change the displayed time when you cross time zones. There may be more expensive units or some future development where they decide to store the time zone information along with the maps, in which case, the GPS unit would then be able to display the correct local time by cross referencing the location and time zones, but I haven't seen it yet.

KuoH

Primary reason is to have accurate time (from satellite) which will be location dependent. I live in France but travel frequently to UK so do not want to physically change the time on the camera for each trip. Time in UK is 1 hour behind France!

 

[jokiin]

we do time and timezone offset from GPS, it doesn't need to be cross referenced, the information is in the data stream already

 

[kuoh]

Like the supposed discount some insurance companies offer if you allow them to plug a data logger to your car's OBD port. It gives them a reason to raise rates for all other drivers unwilling to submit to monitoring, but I'm skeptical of most good drivers actually receiving any appreciable discounts. Maybe 2014 is the new 1984.

KuoH

that is definitely a trend that has been noticed

 

[kuoh]

Is that in the WAAS signal? I wasn't aware that GPS satellites were broadcasting locallized information in the data stream, since they can't direct the broadcasts toward specific areas. Maybe I'll have to look up how that works when I get bored one day.

KuoH

we do time and timezone offset from GPS, it doesn't need to be cross referenced, the information is in the data stream already

 

[jokiin]

we used to do it via a table lookup to give the offset value based on location but it's more work and more processor intensive, we pull the data from the stream now instead

the only annoyance is areas that use DST, this is not carried in the data stream so it can either be managed via an offset setting (not a big deal as it's not something that needs adjusting often) or again via a table based lookup and a set of rules, a lot of work to do and again processor intensive so the offset setting in the menu is an easier way to go

 

[kuoh]

The table lookup was how I thought it would work, but I'm not sure I understand how you get the information from the data stream. Does the GPS receive a different data stream in California than in New York? Other than the WAAS, which is ground based, I wouldn't think so. Or does the stream from the sat contain time zone information for all lon/lat sectors and the GPS looks up local time zone based on that?

KuoH

we used to do it via a table lookup to give the offset value based on location but it's more work and more processor intensive, we pull the data from the stream now instead

 

[jokiin]

the info comes from the GPS, that's about all I can tell you, not because I don't want to tell you but because I don't know the technically correct answer, our engineer worked it out a few months ago

 

[kuoh]

Ok, I understand what you mean now. The GPS chipset you're using is capable of providing the time zone information, but you aren't privvy to the means. I suspect it's probably using WAAS or whatever the European equivalent is. I'm sure it's something that can be clarified with an afternoon of Googling, if Iget sufficiently bored and/or curious one day. Thanks.

KuoH

 

[jokiin]

Ok, I understand what you mean now. The GPS chipset you're using is capable of providing the time zone information, but you aren't privvy to the means. I suspect it's probably using WAAS or whatever the European equivalent is. I'm sure it's something that can be clarified with an afternoon of Googling, if Iget sufficiently bored and/or curious one day. Thanks.

KuoH

if you dig up any info that you think can be applied to a useful purpose I'm always interested

 

[kuoh]

Well you would be in a better position to get the correct info from the manufacturer, as I can only guess. But since you piqued my curiousity, a quick Google search seems to confirm that some sort of table lookup, either lat/lon sector or relative longitude based method, is the only way for now. The GPS satellites themselves don't actually transmit any timezone information, just the timestamp, almanac, and the ephemeris data, from which the receiver calculates its position. Your chipset is probably doing an internal lookup and providing a best guess. Same thing you were doing for yourselves before. In areas where the timezone demarcation line follows a single meridian, it should work fine. In areas where it zig zags, you'll obviously encounter discrepencies.

I suspect the timezone information can and may already be included in the map data sets used by car navigation GPS systems, since it could be just small area attributes added to the overall gigabytes of data already available. But I doubt chipsets designed for the dashcam application would use that method, since the data and storage still costs a lot.

This thread has some basic information for anyone else who might be curious. http://forum.arduino.cc/index.php?topic=166099.0

KuoH

 

[jokiin]

maybe chipset dependent, I'm not sure, I'll ask our engineer and see if he can explain it in English

 

[Jet Lag]

When I leave France my Garmin Nuvi is giving accurate French time. When I get off the ferry (just 21 miles away) in England the sat nav picks up the satellites and displays UK time. How difficult is that?

Perhaps too much to ask of a dashcam!


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[kuoh]

It could be more difficult than you think, considering not all timezones follow straight lines and different DST rules for different countries. The satnav has the advantage that it includes a large map database that can include the local timezone & DST offset for the unit to lookup. The typical dashcam has no such database, which has to be purchased and stored onboard, so it has to perform a best guess.

KuoH

How difficult is that?