> Are GPS allowed to be used as rally computers in stage, and
>TSD events? if so anyone using one, seems like a good idea
I don't know what the rules are in Canada, but on US TSDs they are generally allowed, just not used much. They don't really help that much, since they aren't accurate enough. (If you sent 20 GPS cars down a ten mile twisty road, at the end they would wary as much as a quarter mile. 20 rally computer cars would all be within 100 feet.) Now a GPS with mapping software running, which could be refered to when needed is a help to catch some traps and avoid off course excursions, it just won't keep you on time well enough.
Also most GPS units displays are smaller (so harder to read) than a rally computer, so use on performance events isn't a good idea.
>Ah, I see. Maybe in the future rally computers will all be
>GPS, untill the technology is purfected. I though they (gps)
>where more accurate that they are.
GPS can be very accurate in position - the problem comes when you are moving in an environment that is not ideal for reception of the (fairly weak) signals. Trees and other terrain features tend to affect the number and strength of signals seen, and hence the accuracy. The position updating of most consumer GPS devices is not frequent enough to catch all the bends in the road correctly, so the distance estimation can be off.
Bottom line is that GPS is good for highway travel and (with the breadcrumb display or mapping) determining where you are on a rally route, but I would not trust it as an odometer.
I have used GPS in TSD in Ontario; it is great for deciding when you were looping back into a control.
Pace notes, and when recce is not offered, stage notes will always be the best source of necessary info and there is nothing that GPS will offer that the notes, transit routebook and odo will give you.
Only benefit I can see of having GPS is to give coordinants to rescue helicopter (which we don't have)in case of injury and for TV media production 'virtual stage' images to compare multiple cars.
If there was an advantage of teams having GPS, teams would be using it already. Pace notes rule.
>Pace notes, and when recce is not offered, stage notes will
>always be the best source of necessary info and there is
>nothing that GPS will offer that the notes, transit
>routebook and odo will give you.
GPS could be useful on transits, especially when the route book is less than clear (I won't mention the events involved...). Now that I have a spare GPS, I may start running one in the rally car.
So if you were unsure which road to take because the routebook was vague or lacking info, how would you be able to use GPS? If you knew where the next control was, I'd use a map. Pretty easy. Too much technology, leave the GPS for oceanic navigating.
>So if you were unsure which road to take because the
>routebook was vague or lacking info, how would you be able
>to use GPS? If you knew where the next control was, I'd use
>a map. Pretty easy. Too much technology, leave the GPS for
Some route books now have GPS coordinates for controls & radio locations.
I have probably done more experimentation with GPS for TSD than anyone else I have found, at least in recent times.
> They don't really help that much, since they aren't accurate enough. (If you sent 20 GPS cars down a ten mile twisty road, at the end they would wary as much as a quarter mile. 20 rally computer cars would all be within 100 feet.)
Actually, you can get GPS units that are both very accurate and have a fast report rate.
An example is the Garmin GPS16A. http://www.garmin.com/products/gps16a/ It is an "agricultural" GPS with a 5Hz update rate. If you measure the distance between the position reports, you actually get a very accurate mileage. I have been running mine against the odo pulses of my car to measure linearity.
Even better is to integrate the velocity outputs, however even the GPS16A only has a 1Hz output for velocity.
I've had some help and advice from Garmin.
You can calibrate a GPS odo just like any other input. Once calibrated, I have mine within 0.01 mile linearity over 20 miles. That is good enough for TSD [though I think I can improve it].
People said laptop computer clocks weren't accurate enough for TSDs. I've done reasonably well with them.
The other interesting thing is satellite signal, providing you have 3 satellites or more, even on a 2D non WAAS fix, they are still "accurate enough". With a bunch of satellites and WAAS their position reports (or should I say the differences between them) are pretty good.
Now, don't use the "tripmeter" on your average GPS as an ODO. They have some inherent flaws in the logic they use to increment. (My Magellan Meridian Platinum for example, has a very inaccurate tripmeter).
PS another issue is latency. I think the off the shelf handheld 1Hz GPS units out there might not be quite good enough. The 5Hz GPS16A seems ok.
This year I've been using a Garmin Etrex Vista unit in conjunction with my "00" duties at Ojibwe and Headwaters.
We have a database that includes dd mm.mmm lats and longs for every intersection we go through plus all control locations on the OFPR and HW routes.
First of all, let me say we still use a rally computer in the car, the etrex is no replacement for that!
Where it is handy, or at least I think so, is having a backup codriver if/when Brenda gets busy in the car with paperwork or looking out for safety issues. I can download all the waypoints (intersections) build a route, waypoint to waypoint, upload it to the etrex, and then tell it to navigate. With a customized tripmeter display, I have Time of Day, Direction to next Waypoint (arrow), Speed, and Distance to next Waypoint.
Admittedly, its really a third tier backup, as by the time we really are "00", we've been on the road six or seven times already in the last two months.
I can pull up to a control and be able to ascertain immediately if they set up in the right place (Of course, Advance and '000' have checked that too).
I always have time of day (and I have yet to note a >1 sec variance between what the "atomic" radio controlled clocks report and the GPS time)
I certainly think that with a more 'industrial grade' GPSr, with a higher output rate, and the advent of tablet PCs and even the newer "Smart Displays" you could easily have a computer listening to the nmea sentences coming from the GPS, as well as reading the pulse rate of the car's VSS to establish a very reliable and sufficiently accurate position and speed. Throw in an accelerometer oriented laterally, and you could drive through the twistiest tunnel on the continent and still be able to have an accurate moving map.
That brings me to the next point: Reading a moving map is only as accurate as the map itself. There isn't a retail GPSr out there that has a sufficiently accurate map built-in to be able to navigate the Minnesota rally roads, and I suspect that goes for most rally road areas. I can trust the etrex on the rally roads because I have been to each of those points before, and recorded a waypoint. I've tried blind navigation by the GPS alone (trying to follow the moving map) with only disasterous results...
In the long run, the desired result is that, to paraphrase: You mileage *won't* vary.
>That brings me to the next point: Reading a moving map is
>only as accurate as the map itself. There isn't a retail
>GPSr out there that has a sufficiently accurate map built-in
>to be able to navigate the Minnesota rally roads, and I
>suspect that goes for most rally road areas. I can trust
>the etrex on the rally roads because I have been to each of
>those points before, and recorded a waypoint. I've tried
>blind navigation by the GPS alone (trying to follow the
>moving map) with only disasterous results...
Using the right tools, your navigation accuracy should be dependent on the quality of the maps you are using. NMEA output to a laptop running a program that uses properly registered accurate maps can be very close. We've run Fugawi with the Canadian topos and been able to determine where we are on a particular road. Of course, this assumes that your rally roads are accurately shown on the topos.
I've also used the breadcrumb trail on the GPS screen to determine where I was on a paper topo (you can see the road configuration quite well).
>Only benefit I can see of having GPS is to give coordinants
>to rescue helicopter (which we don't have)in case of injury
I used a GPS and our satellite phone to do exactly this in Oregon. The emergency dispatcher was surprised that we had the information, but gratefully received it and passed it on to the responding helicopter.
In that case, the GPS belonged to a control worker. But it did prove itself useful in the way you imagine. I would consider carrying one myself in the future.
I post the following not to express an opinion either way, just as a public service and to show off:
GPS (not GNSS) can be:
- parallel channel or multiplexing (older models)
- high noise (cheap) or low noise (less cheap)
- single frequency or dual frequency
- code-only or code & phase and/or phase-smoothed code
- autonomous and/or code & phase differential (RTK) and/or code differential (DGPS)
DGPS corrections can be:
- differential position corrections (less accurate) or
- PRN observable corrections (corrections calc'd for each code observable from each satellite)
- PRN observable corrections smoothed by carrier phase
They can be provided by:
- another local receiver sending via radio modem, cell phone etc OR by some sort of service
- a wide area service (WADGPS) such as Racal, OmniStar, Satloc, WAAS (free), GPS-C (free), Coast Guard (free)
Lets look at both ends of the spectrum: a Garmin handheld ($200) and a Leica Dual frequency geodetic receiver ($40,000)
Garmin: parallel, high noise, single freq, code only, autonomous or code differential (DGPS), DGPS=position corrections only, some come with WAAS built in, they are capable of being corrected by any of the above-listed WADGPS services given a connection to the appropriate radio or satellite receiver.
- autonomous uncorrected with suitable sat coverage and geometry 10 to 15m
- WADGPS with suitable sat coverage and geometry +/- 5m
Leica: parallel, very low noise, dual freq., code & phase, autonomous or DGPS or RTK capable, DGPS=individual channel corrections smoothed by carrier phase if available, no WADGPS service built-in, capable of being corrected by any of the above-listed WADGPS services given a connection to the appropriate radio or satellite receiver.
- autonomous uncorrected with suitable sat coverage and geometry 10 to 15m
- DGPS from second local Leica receiver +/- 30cm
- WADGPS with suitable sat coverage and geometry +/- 1m
- RTK from second local Leica receiver with suitable sat coverage and geometry +/- 2cm
A good setup for rallying would be:
A 1 or 10Hz GIS-type single frequency receiver capable of wide-tracking loop for performance under canopy, corrected by GPS-C (highly accurate free service of the gov't of Canada, broadcast on MSAT - proprietary sat receiver one time cost of $1500CDN)
This is a low noise, low latency setup that could provide pretty good time and 1 to 2m DGPS accuracy under sparse canopy. Total cost maybe $5000 up.