Route recalcualtion

[Paul Wakefield]

I have a suspicion this has been answered before on this site but I can't find it so any help gratefully received.

I have just set up my National Rally route in Mapsource which I have done as one route with lots of via points - maybe I should have done it as 15 or so routes but I didn't! Inevitably I will go off route at some point and the route will recalculate.

Question: When it recalculates, is it just to the next via point or does it recalculate the whole route (as the preferences in Mapsource and the unit may be different)? If the whole route recalculates, there is going to be a significant time cost and my chosen routing may get altered.

I've never tried it but, if I switch recalculation off, I presume I am on my own until I get back to some point on the route that the GPS recognises?

Paul

 

[Howard Millichap]

As far as I know it will recalculate to the next "waypoint". I don't know about via points. The software was changed in v2.70 on my SP3 because it used to recalculate to the end of the route.
My advice is to turn the facility off and make your own way back to the route. That way you retain all the original route and you go where YOU wanted to go in the first place.

 

[PanEuropean]

Question: When it recalculates, is it just to the next via point or does it recalculate the whole route (as the preferences in Mapsource and the unit may be different)?

Hi Paul:

The last time I looked into this in any detail was about 3 years ago, just when the 26xx series of GPSRs was coming out to replace the StreetPilot III as the new top of the line units.

The way things worked back then was as follows:

1) The GPSR would make up to three 'quick recalculations' that were intended to get you back onto the existing route line in the shortest possible distance - in other words, to re-capture your route without making any changes to your route.

2) If it appeared to the GPSR that you were trying to get back onto the original route (i.e. you were following the prompts), the GPSR would continue to route you back onto the original route without modifying it.

3) If the GPSR made its three 'quick recalculations' and you ignored the prompts provided three times in a row, it would then do a full recalculation of the route. The full recalculation would create a new route (from scratch) to get you to the next waypoint along your stored route. However, if you were very close to passing abeam the 'next waypoint', you might get routed to the subsequent waypoint along your route, rather than to the 'next' one.

Again - that was how it worked several years ago. Processing power has increased by a factor of 10 since then, so it is possible that the GPSR may no longer do the three 'quick recalculations' any more. The motivation behind the 'quick recalculation' was to speed up the route recalculation process - something that may no longer be a concern with the super-fast processors in the 27xx and 28xx series.

In any case, intermediate waypoints that you create in MapSource by dragging your route line around are treated with the same respect as intermediate waypoints that you create manually by making a waypoint and including it in your route. So, you don't have to worry about the GPSR discarding your point to point preferences when it recalculates. As long as you have not already passed abeam an intermediate point, the GPSR will try to take you to the intermediate point when it does the recalculations.

Hope this helps.

By the way... many years ago, the lack of processing power (recalculation power) was actually a benefit to rally organizers, because the GPSRs would take a very methodological approach to route recalculation, and never get 'creative' about trying to get the rider to the destination faster. Nowadays, the GPSR route software is a lot more sophisticated, and the device itself can recalculate much faster. This could, I suppose, have unwanted effects for those who are constructing rallies. If you find that the GPSR is being 'too clever' about recalculating rally routes, and you can't find a way of disabling the automatic recalculation feature, let us know, and maybe the software engineers can provide us with a 'rally' setting, which would tell the GPSR to not ever change the course of the pre-programmed route, under any circumstances. In other words, only do recalculations to get the rider back onto the existing route, never change the existing route.

As most of the regulars here know, some of the Garmin software engineers are moto riders, and they would understand exactly what we were asking for, if it ever becomes necessary to ask for it. I just don't know if the GPSR will handle rallies the way we want right now (the 'old' way), because I don't ride in rallies myself.

Michael

 

[Paul Wakefield]

Thanks to you both for your advice. I'll see how it goes - I'm using a 2610 so I suspect it will work as Michael preidcts which should be fine.

Michael,

I like the idea of your "Rally"setting in any event so that a Route you've sweated blood over doesn't get changed by a GPSR that "knows best" I think you would basically want an option to a) never change the route (without user intervention) and, in the event of deviation from track, the option either to pick up the route again at the point of deviation or the point on the route nearest to your present position.

Cheers.

Paul

 

[PanEuropean]

Hi Paul:

What you suggest makes perfect sense for us (moto riders who construct routes intended to take us over specific roads, without concern about 'fastest time' to destination). However - 99.9% of the cage drivers out there just want to get from A to B in the simplest manner possible, and these are the folks who drive software development. But, Garmin has always been pretty good about catering to the other 0.1% of us, as long as we can explain what we want clearly and simply.

Anyway - if you have a 2610, I am pretty sure that it will do the 'three quick calculations' routine as I explained above. I remember doing the testing of that sub-routine when it was developed in late 2003 - early 2004.

Michael

 

[HMR]

Bottom line is:

If you allow the unit to recalculate you will find that the result is entirely unpredictable! It depends on what GPS model you have, what firmware version you are using, where you are at the moment, etc.

I would recommend you to:

- Use several shorter routes and not one very long.

- Set "Off-route Recalculation" to OFF to prevent the GPS to "destroy" your route automatically. Use instead manual initiation of recalculation. This you do just by pressing two buttons. "NAV", "NAV" or "NAV", "ENTER" depending on GPS model.

 

[PanEuropean]

If you allow the unit to recalculate you will find that the result is entirely unpredictable!

No, not really. In fact, if you allow the GPSR to recalculate on its own whenever it wants to, the result will be VERY predictable: You will be routed via whatever path best conforms to the preferences that you set in the GPSR (fastest/shortest, on/off highway, with/without toll roads, etc.).

What we have to keep in mind is that the vast majority of GPSR users really don't care what route they have to take, they just want to get from A to B in accordance with their preferences. The GPSR software is designed to do this as best as it possibly can. Naturally, newer (more powerful processor) GPSRs and GPSRs running the newest software and newest maps do the job better than older ones.

If your routing wishes are more specific - as they often are for touring and dual sport motorcyclists, who are frequently more concerned about what roads are followed, rather than just getting from A to B, then you need to keep in mind that you will need to provide a bit of specific direction to the GPSR to ensure it follows the route that YOU construct, rather than 'improving' it on the fly. This isn't hard to do, but the catch is that you need to be aware of the need to do it.

Michael

 

[st13phil]

The last time I looked into this in any detail was about 3 years ago, just when the 26xx series of GPSRs was coming out to replace the StreetPilot III as the new top of the line units.

The way things worked back then was as follows:

<< snip >>

3) If the GPSR made its three 'quick recalculations' and you ignored the prompts provided three times in a row, it would then do a full recalculation of the route. The full recalculation would create a new route (from scratch) to get you to the next waypoint along your stored route. However, if you were very close to passing abeam the 'next waypoint', you might get routed to the subsequent waypoint along your route, rather than to the 'next' one.

Again - that was how it worked several years ago. Processing power has increased by a factor of 10 since then, so it is possible that the GPSR may no longer do the three 'quick recalculations' any more. The motivation behind the 'quick recalculation' was to speed up the route recalculation process - something that may no longer be a concern with the super-fast processors in the 27xx and 28xx series.

FWIW, I think that the same recalculation algorithm is still used on the 2720.

A week ago I was travelling back up through France from Dijon to St-Omer and had constructed a route in Mapsource that took me on N-roads from Dijon to near Troyes and then hopped onto the Autoroute up to a point approx 20 miles south of St-Omer where it reverted to N-roads. The only via points - created in Mapsource by "banding" the route - were on the first leg of the journey to keep me off the Autoroute south of Troyes and on the last leg to keep me off the A26 as I headed in to St-Omer.

As we were approaching Troyes I decided that I'd rather ride the N-roads up to Reims so hit the "Detour by Roads in Route" option on the GPSR to kill off the first Autoroute section. This was fine but (predictably) it then tried to route me back onto the Autoroute further north. So I used the Detour option on that part too and the GPSR quite reasonably in light of my set preferences found an alternative route on Autoroutes via Paris At that point I just muted the voice prompts and just carried on riding a route I was happy with.

I rejoined my "original" route on the A26 north of Reims and the repeated route recalculations stopped so I un-muted the voice prompts. Despite multiple route recalculations (probably in the order of 20 or so!) on hitting my next via point south of St-Omer the GPSR dutifully reverted to the N-roads route I'd originally planned.

 

[Fanum]

Paul....you may find another problem if your route is circular ie starting and finishing at the same point.

I cocked up a ride recently because I'd planned a circular route....as soon as the first minor deviation happened, the GPS recalculated and realised that the best way to get to the destination was to turn round and go back the way we'd come

For circular routes, you either need to plan a rout to the farthest point as a destination then another to get back to the starting location, or turn auto recalc OFF.

Lesson learnt

 

[Paul Wakefield]

Well, Bill hit the nail right on the noggin. I had a circular route planned on the Saturday, short kip then off at 4am for the next part on Sunday. 500 yards from home GPS decides it can do a much shorter route by leaving out the whole circular bit and just do the Sunday morning route thus obliterating my careful planning. I was slightly surprised as recalculation was set to manual. But after a few recalculations trying to send me back the way I came, I just switched the route off.

Fortunately all the waypoints were of course still intact so, at each control, I just calculated the route for the next one. This was probably better in fact and I think will be the approach I adopt next year (overall plan in advance to get an overview of desired route, download waypoints and then calculate and review at each checkpoint). Because I had done the planning, I knew pretty much the way I wanted to go so it was fairly easy to review the proposed route in overview before setting off. There was only one leg where it wanted to go a completely different route so I just slammed in a waypoint on a selected road and that sorted it - the only time I had to use a map (I always carry one; I see GPS as complementary to maps not a replacement) in the whole rally. I think it shows that I have got the road preferences in the 2610 fairly well sorted for me. The route calculations that were produced were I thought both predictable and consistent.

It was great not having to memorise routes and road numbers, having an ETA and distance to go and having the camera warnings (a 2820 does sound attractive with the possibility of audible warnings but I don't think I'll be allowed one for a while). It made the rally much easier and I could enjoy the ride more. Which I did in spades (though the saga of the headlight bulbs was a different and rather embarrassing story).

Paul

 

[Kritou]

Paul....you may find another problem if your route is circular ie starting and finishing at the same point.

I cocked up a ride recently because I'd planned a circular route....as soon as the first minor deviation happened, the GPS recalculated and realised that the best way to get to the destination was to turn round and go back the way we'd come

For circular routes, you either need to plan a rout to the farthest point as a destination then another to get back to the starting location, or turn auto recalc OFF.

Lesson learnt

Does it make any difference if you rename either the start or finish point - or for that matter shift one of them a few yards?

 

[PanEuropean]

Paul:

Is Oxfordshire close to the town of Oxford?

I just landed in Oxford, England this afternoon, and have two days to kill here before departing to Switzerland Wednesday afternoon. Would be nice to get together for a coffee if you are close by. I am at the Oxford Hotel. I'll send you a PM with my cell phone number - text me if you are nearby.

Michael

 

[Fanum]

Does it make any difference if you rename either the start or finish point - or for that matter shift one of them a few yards?

No......the point is still closer to the actual position if you've only just started off on the route than the other points on the route , so it'll turn you around.

 

[HMR]

No, not really. In fact, if you allow the GPSR to recalculate on its own whenever it wants to, the result will be VERY predictable: You will be routed via whatever path best conforms to the preferences that you set in the GPSR (fastest/shortest, on/off highway, with/without toll roads, etc.).

I don't agree. Not at all actually...

With the unit set to choose "fastest" road and all other preferences in default position the route calculation in the unit works fairly well. I use this setting often when I use the navigator in my car. Here I prefer bigger roads and the unit makes good choises in most cases. When in the car automatic "Off-route Recalculation" is sometimes ON but mostly OFF.

With the unit set to choose smaller roads, avoid motorways, etc with the purpose to ride MC on smaller roads the routes calculated by the unit may be predictable OK, but most often not the roads you want to ride on. I have tried all kind of settings in SP3, 276C, Quest and SP2610 and found routing in the unit almost worthless for this purpose. To my opinion it's only in MapSource that it is possible to efficiently create routes on "nice" roads. When on the bike automatic "Off-route Recalculation" is always OFF.