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Old 23-10-2013, 14:58   #1
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Autopilot and GPRMC functionality.

Dave et al.
First I (again?) do want to express my gratitude for the OCPN program and its outermost functionality. My last experience is a four month cruising around the Baltic Sea always using the last edited beta versions. I’ve a rather old boat with more or less aged electronic gears but the serial multiplexer is combining them all to a great function and useful presentation. That together with the possibility to simultaneously use both raster and vector charts makes OCPN outstanding. My humbleness for the idealistic team of developers is also every day in my mind. Thanks all of you. That said to my topic.

I’m not sure if this topic is OCPN or autopilot, AP, dependent so please advice.
When navigating towards a way point using a route the GPRMC sentence is created by OCPN and transmitted to the autopilot. My AP, Simrad WP30, reads the desired course and course line deviation. My topic now is when a relatively great course deviation occurs for one or other reason the AP sometimes make a vigorous turn to follow the course line of the route. In most cases I instead would like the AP to head to the destination WP and thus very slowly return to the former course line. If I’ve have, say, two hours to go there is no need for a strong turn to return to the fictive line. Ok - when a course line is set to avoid some hinders there could be a reason for a powerful action to return to the line but at least for me that’s a rare situation. What I sometimes do now, if I for example had to give way for a freighter, is to delete the route and make a new from the present location.

Is the described behaviour anything that is controlled by OCPN or the AP? If OCPN - is it possible to control the speed of the return to the course line and then insert a factor as a course property and thus make it possible to control the course correction behaviours? That factor may also be dynamic as a multiple of the distance to the destination?


Thanks for your up coming discussions/Håkan
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Old 23-10-2013, 18:25   #2
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Re: Autopilot and GPRMC functionality.

That is controlled by your autopilot, not OCPN. You need to reset the cross-track error or navigation data to simply go toward your waypoint without going 90* back to your original route track.

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Old 24-10-2013, 07:15   #3
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Re: Autopilot and GPRMC functionality.

Quote:
Originally Posted by Hakan View Post
Dave et al.


I’m not sure if this topic is OCPN or autopilot, AP, dependent so please advice.
[FONT=Arial][SIZE=2][FONT=Arial]When navigating towards a way point using a route the GPRMC sentence is created by OCPN and transmitted to the autopilot. My AP, Simrad WP30, reads the desired course and course line deviation. My topic now is when a relatively great course deviation occurs for one or other reason the AP sometimes make a vigorous turn to follow the course line of the route. ................
Yes I agree, if something can be done inside OCPN is probably the best. There are different brands of autopilots and to handle this issue on the autopilot will give different solutions. Of coarse you can do this manually by going to auto on the autopilot (Raymarine) and wait till you are back on the line. If OCPN can handle this that is a better solution in my opinion.
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Old 24-10-2013, 07:31   #4
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Re: Autopilot and GPRMC functionality.

Can you just drag the previous waypoint of the route to a location that intersects the route with the current position of the vessel? Basically move the route leg to the boat. That would effectively force OpenCpn to recalculate the XTE to zero.
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Old 24-10-2013, 07:40   #5
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Re: Autopilot and GPRMC functionality.

Capt.Alex....

That is exactly what I do after diverting for a CPA crossing. Just drag the previous waypoint. Or, if the previous WP is not onscreen, sometimes I add a new waypoint at the ownship present position.

Dave
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Old 24-10-2013, 07:57   #6
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Re: Autopilot and GPRMC functionality.

Hakan, Your feelings about O are echoed by me.
Our autopilot does not behave like yours so I want to understand what you are saying. Are you saying that if you do a dodge for another vessel, and then re-engage the AP, that it turns sharply to the closest part of the original course line, possibly a 90 degree turn?

I have never had that. Ours is a Ray.... system. When we do a dodge in track mode, we simply press the + or - buttons, execute the dodge, and leave it so (we do not apply opposite adjustment) the boat slowly creeps back on course ignoring the XTE. BUT if we cancel track mode, then execute a dodge, and then re start track mode, we get large XTE alarm. To correct this we "De-activate" the route on OpenCPN, and then "Activate", this has the effect of zeroing the XTE. To make it LOOK better on screen, we drag the previous waypoint, (The one astern of us) so that the course line can be viewed against the track line.

I hope I have not confused this even more.....
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Old 24-10-2013, 11:45   #7
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Re: Autopilot and GPRMC functionality.

This is a wonderful forum. Nice and discerning contributions from all you,thanks.
colemij..
Yes that's what I thought. O is reporting heading and course deviation, e.g. cross tack error. The AP have no idea where we are and just respond to signals from O. The AP contains a "simple" regulator and we can normally adjust gain and integration, sometimes called sea filter, to get a slow or quick response. So we have to focus on O or ourselves.
Jan..
Yes, switch to Auto for a while until back on line is the method I've also used many times. But since being a bit lazy I did want to discus for a more convenient method. (Being lazy is one the features that's evaluating mankind?)
Capt.Alex and Dave..
Ok, thats a handy method especially compare to deleting the route and create a new destination WP and restart the AP Nav mode. But all these adapting methods forces me to raise from by comfortable position and move myself down to navigation table for some more or less intelligent actions. But let me guess that you Dave have got some similar thoughts on your way to Bahamas? And may has concluded that incorporating of a adaptive course deviation handling will lead to a rather complicated coding and not less to a not so understandable user interface?
SY Gilana..
Yes, despite my poor English I feel you've got my points without confusions. The way your Ray.. works seems not so bad. To dodge by using the +/- key to achieve temporarily changes while still in Nav mode sounds nice. So I was forced to have a deeper look into my Simrad manual and guess what: Yes, there is a nearly hidden sentence describing the same functionality I've missed! ( And I use to describe myself being manual reader.:-)) My manual says that after a course change using the +/- keys the course "will while in Nav mode gradually return to the original track". Many thanks for that hint, I'll try it next cruising event.

So my conclusions are that I can proceed my lay back position and just let the AP do its job and Dave can keep O nice, understandable and simple to handle without complicated adaptations.

Thanks, it's been a pleasure to learn from all of you/Håkan
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Old 26-10-2013, 07:00   #8
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