How close is close

Re: In an ideal world

I actually have found this thread interesting and have learned something which is that not everyone appears to understand GPS they way they thought they perhaps did. Perhaps a mag article explaining the processes may be an idea, as I certainly think that missing a waypoint without an alarm and then following a track to the next point without realising that you could be 'standing into danger', somewhat disconcerting. At least an alarm could alert you to the fact and put you on your guard.

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Re: In an ideal world

" I certainly think that missing a waypoint without an alarm and then following a track to the next point without realising that you could be 'standing into danger', somewhat disconcerting. At least an alarm could alert you to the fact and put you on your guard. "

I think you will find that almost all modern units obey the 90 degree rule and do alert. I agree totally with you that any system that just triggered onto the next waypoint without the need for the a human decision is dangerous. However if you are missing a waypoint then I would rather be alerted to the fact and offered a choice than not alerted at all.

The way in which your own GPS/Plotter works should be understood by every skipper - its just as important as the ability to use paper charts.

<hr width=100% size=1>Paul
 
No - actually it DIDNT trigger the next waypoint - just showed me getting further and further away from the original one AND I HAD passed to 90 degree rule. Hence my reason for the orignal question.

p.s. The reason for the question was to further my understanding of the GPS workings - anyway how many people ACTUALLY know everything about a product and can recite the instruction manual. None I expect. Can you do a mail merge in Word, or know all the mark up tags in the forum ???
p.p.s. I know chart work is important and that the GPS is an additional tool in the tool box, not a replacement.
p.p.p.s I would think many GPS's are not connected to autohelms, rather than many are!!

<hr width=100% size=1>Adrian - <A target="_blank" HREF=http://www.arweb.co.uk/argallery/kelisha>More Pics of Kelisha</A> /forums/images/icons/smile.gif
 
Sorry I got it wrong on your unit. In whhic case I was barking uip the wrong tree as regards your problem sp others were giving the right advice for you and me the wrong - but what it has exposed is this whole question of understanding the principles of passing onto the next waypoint.

Having checked manuals I am finding a pattern that is news to me. The small handheld units do not seem to have the 90 degree rule - in fact they even have other rules such as time to waypoint etc - all suitable for land use as well as marine use. Whereas the dedicated marine plotters seem to have the 90 degree rule.


I am now going to do some research and find out which makes of plotters have the 90 degree rule and which do not. I will be looking at the dedicated fixed units for this survey and will publish the results.




<hr width=100% size=1>Paul
 
Re: In an ideal world

Well - I was all set to disagree, but just in case, I read the manual - I know, I know real wimp to RTFM, but just once ...

So in the manual for my (Raything 630) plotter I found ...

==============================================
If you have set the Arrival Alarm when you set up your system, the alarm
buzzer sounds and a message is displayed when either of the following
conditions is met:
• The distance to the target point is less than that specified for the Arrival
alarm.
• Your vessel reaches the closest point of approach to the target (that is, it
crosses the perpendicular to the track, and through the target.
The alarm is cleared after 7 seconds. You can clear the alarm earlier by pressing
any key.
============================================

Seems pretty unequivocal. Guess I'd never seen it because I dont actually tend to use waypoints linked as a route, as the plan tends to be discarded shortly before casting off (in MoBo days I did use a route), as wind tends not to have read the met fivecast, and seldom does as advertised.

Anyway, thanks, I've learned something - which is usually a good thing.

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Shall I let Mike know or will you /forums/images/icons/wink.gif

anyway what I need to confirm is :-

Does my GPS 72 have the 90 dgree rule ? Can any tell for positive ??
if not then how does it know when to go onto the next waypoint ?

forget the bit about not being on course and the best way back on course !!

<hr width=100% size=1>Adrian - <A target="_blank" HREF=http://www.arweb.co.uk/argallery/kelisha>More Pics of Kelisha</A> /forums/images/icons/smile.gif
 
I just downloaded the GPS 72 unit manual to check and it does NOT have the 90 degree rule - it has two new ones based on time and speed!! These are used in land GPS use.

I am going to post the results of my research on this site because the way it is looking is that small hand held units do not have it - the dedicated fixed units do have it.

The fact that the 90 degree rule has had this exposure is good because at least those who have it will realise that the alarm may not mean they are within the proximity of the waypoint. unless they accept the next waypoint they will be left with having to turn back and head for the current one.



<hr width=100% size=1>Paul
 
Quick reply

Sorry, point I was making is that there are a lot of units out there that don't work this way; for that reason any piece of advice or article would first have to counsel to get to know individual workings of units, by using, as manuals sometimes don't even scratch operational protocols as I have found out to my cost when trying to operate multiple navigators on test.

I suspect we are almost saying the same thing, in that respect at least.

As for which system is safer well, of course, in reality the minute you are off plan then lady luck holds all the cards and it very much depends on a whole series of factors.

What I do know is that many people I come across have not gained the ability to hop to next waypoint on a route and those that have don't always know whether XTE is indicated from hop-to point--next waypoint or old waypoint--new waypoint when they do. All of that is not helped by some particularly convulted routines to do so in some cases. So one could argue that a system that knows when to give up on a lost cause is probably a good thing for them, perhaps, especially if alert boundaries are left on default settings of just a few metres.

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You have hit on the area where most GPS software developers fail. A combination of different requiremnts must be used to identify safely if you have passed a waypoint. For example if you miss the range circle, which usually has a user determined radius, then you need something like crossing the bisector(s) of the angle(s) of intersection of the legs of the route.

Even expensive software such as MaxSea only uses a circle which seems to indicate a lack of understanding of the problem by software engineers.

The only equipment I have experienced which consistently and safely recognised waypoint passing was from AP (Phillips/Magnavox), now Leica.

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Re: Quick reply

"Sorry, point I was making is that there are a lot of units out there that don't work this way; for that reason any piece of advice or article would first have to counsel to get to know individual workings of units, by using, as manuals sometimes don't even scratch operational protocols as I have found out to my cost when trying to operate multiple navigators on test."

Agreed

"As for which system is safer well, of course, in reality the minute you are off plan then lady luck holds all the cards and it very much depends on a whole series of factors."

You are surely ducking the issue there and not answering the direct questions :-)

I agree totally about Lady Lick - but my questions are based on what is best in a given situation and you have not answered that - yet advice is often published about how to both avois a probelm or get out of a probelm - in this case the two examples given with the questions are clear - so go on try and answer :-)

"What I do know is that many people I come across have not gained the ability to hop to next waypoint on a route and those that have don't always know whether XTE is indicated from hop-to point--next waypoint or old waypoint--new waypoint when they do. All of that is not helped by some particularly convulted routines to do so in some cases."

100% agree

So one could argue that a system that knows when to give up on a lost cause is probably a good thing for them, perhaps, especially if alert boundaries are left on default settings of just a few metres. "

I do not know what you mean by give up???

The 90 degree rule giving you the option to carry on to the bext waypoint when you have just missed the current point by 100 metres because of a diversion for a big freighter is hardly a difficult question - please try and answer it. :-)



<hr width=100% size=1>Paul
 
A rose by any other name

I reckon that what we need is a Missed Your Wapoint alarm to sound as we pass the waypoint outside its zone - then we could have the choice of continuing to the next waypoint or turning right to the existing one.

Now does calling it a Missed Waypoint alarm make everyone happier? :-)

<hr width=100% size=1>Paul
 
Plain English

My use of phrase 'give up' = unit gives up trying to seek old waypoint and hops to next. So did answer really, but badly.

What would I prefer? It's actually a good question. I grew up with the very first electronic navigators (old Deccas and sat navs) and started writing about boating at around the time they started to become 'affordable' (as in over £1000 for the most basic set) and so have grown up with the quirks and kind of got used to having ultimate control. An auto-anything action is therefore a bit foreign to me and not always welcomed as I like to call the shots. On the other hand, stuck on a strange boat with a navigator I haven't used before and tracking off a course (I rarely sit on my own nav courses, for various reasons!) having a GPS or plotter auto-hop to the next waypoint irrespective of distance off the previous one is quite welcome, as long as it comes with a healthy alarm.

Last few years I've run systems that predominantly use your preferred approach and don't have an issue; quite welcome in most respects.

In fact when using GPS linked to autopilot (a practice that has been denied as being commonplace I think elsehwhere in this thread but that in fact is becoming very commonplace) there are some very good safety reasons to not have a boat overshoot its waypoint when in track mode. That sounds odd for track mode surely = on track does it not? Well no, of course not necessarily, if dodging this and that. Human beings, when confused, do some strange things (judging by my own actions). Course computers, when confused, do some amazing things!

There you go, you eaked it out of me (I think). Mind you, missed my train in the attempt.

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Re: Plain English

I agree, without qualification with everything you said.



At the end of the day it is only a Missed Wapoint Alarm as you pass the waypoint outside its proximity zone - after that alarm you have to turn back to hit it - before the alarm you can still turn towards it without going back. That alarm with its options just has to be better than no alarm at all and hence no presented options.


<hr width=100% size=1>Paul
 
Sorry Paul, my note was a poor attempt at humour following your public revelation that Powerskipper's XTE is smaller than her proximity alarm. Do you know her well then ? /forums/images/icons/smile.gif

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Sorry, don't want to miss being included in the first post I'm likely to see go passed the 100 mark!

BTW anybody found a lead to connect a Garmin Etrek direct to a Dell Axim yet?

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There have been several references to the effect that for a unit which only alarms when in the circle of arrival, ie the 90 degree rule is not used by the unit, one has to double back to the waypoint. Given that before one does anything one should determine exactly where one is and then see that the next course is safe, I would have assumed one would just check that the course from the current position to the next waypoint was clear of dangers and manually advance the unit to the next waypoint if so. I am afraid I do not see the necessity of doubling back to the waypoint.

I think a lot of the arguments are based around personal preferences rather than real problems, but I would have thought that whatever ones stance on that, if one was going to miss the waypoint by anything other than a trivial amount then one was navigating sufficiently responsibly to actually know that was going to be so before you got to the stage of missing it and relying on the 90 degree line alarm. If one knowingly alters course (as to avoid shipping, etc) then one has changed the navigation plan and the plan should be reassessed along the lines of "where am I going to now (any dangers?)?", "when I get there where do I go next?", "if next is to waypoint (any dangers?)", "if next is to the subsequent waypoint (any dangers?) and if no dangers advance unit to next waypoint", "if dangers to current or subsequent waypoint plan a new course to destination".

If one suddenly finds one is accidently off course (and that can happen from some important other distraction) then I would have thought the immediate concern would be to urgently assess ones current position and heading, and then go through a similar process as above.

Given that one should be navigating so one knows if one is off course (and that is a trivial task given we are using a GPS and maybe even a plotter) and if you are off course or have changed course one should replan, I am not sure that much of the arguments about 90 degree lines and circles of arrival are of much merit.

{also thinking "this might be worth another few posts"!}

John

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by MainlySteam on 14/10/2003 23:15 (server time).</FONT></P>
 
Your points about the practice of what you should be doing are in total agreement with my own views.

"I would have assumed one would just check that the course from the current position to the next waypoint was clear of dangers and manually advance the unit to the next waypoint if so. I am afraid I do not see the necessity of doubling back to the waypoint."

In fact I have been arguing against this silly being forced to double back policy throughout this thread.

I agree - in any event you can advance the unit to the next waypoint but its nice to have this offered to you with an alarm to say you are now increasing your DTG and have passed the waypoint. Its just a reminder and option to save you doing a manual advance although it still requires your approval.

"If one knowingly alters course (as to avoid shipping, etc) then one has changed the navigation plan and the plan should be reassessed along the lines of "where am I going to now (any dangers?)?", "when I get there where do I go next?", "if next is to waypoint (any dangers?)", "if next is to the subsequent waypoint (any dangers?) and if no dangers advance unit to next waypoint", "if dangers to current or subsequent waypoint plan a new course to destination"."

Totally agree - however the offering of the alarm does no harm and cannot be considered dangerous - in effect you could see that you had paassed the waypoint when the DTG started to increase, it being at that moment when an alarm sounds to say this is about to happen and you may choose to accept and hence advance to the next waypoint OR double back.

"If one suddenly finds one is accidently off course (and that can happen from some important other distraction) then I would have thought the immediate concern would be to urgently assess ones current position and heading, and then go through a similar process as above."

I again agree but the very fact that there is an alarm telling you - "Hey, you are now at the point of passing the waypoint you are heading to .... you need to decide what to do" - is a good thing - the very fact that the drift off course has been accidental means that an alarm is very appropriate. Again such an alarm is not dangerous but helpful.

"Given that one should be navigating so one knows if one is off course (and that is a trivial task given we are using a GPS and maybe even a plotter) and if you are off course or have changed course one should replan, I am not sure that much of the arguments about 90 degree lines and circles of arrival are of much merit."

I think you are missing the point. The issue was that the alarm that tells you that you are passing the waypoint having missed it and should decide what to do was considered dangerous by some - that was countered by myself. For the reasons I have stated above I consider that an alarm for this is a good thing. The miracle here is that to get this simple point across has taken almost 100 posts!!!

Surely if you are diverted by shipping and only just missing your waypoint then its rather nice to ahve the larm go instead of just watching a DTG counter waiting for it to start and increase?

The bigger issue is that the skipper should know on what basis their electronics work and hence understand whatever alarms etc they have got.


<hr width=100% size=1>Paul
 
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