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Old 14-08-2011, 17:06   #1
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Two Questions About OpenCPN

hello Dave,
i have 2 Questions,one is how open Heading & Real - time kinematic(RTK) these two functions,i think these two functions are very importance to pilot.
two:when use zoon in to vessel,the vessel icon is the small icon always,i think the vessel icon should be variation according to the scale vary。
thanks for you tell me how to open these two functions.
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Old 15-08-2011, 00:08   #2
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Re: Two Questions About OpenCPN

smart...
As cagney already told you in the other thread you started for almost the same topic, RTK is more a function of a special GPS receiver than a navigation software. I also wonder how many of our users (Hamish did, I know) have even seen such a thing.
Anyway, to add these functions you can do a couple of things:
1) Learn C++ and implement them yourself
2) Get someone to do it
3) File a feature request at OpenCPN::Tracker All Projects: Tasklist and wait if someone decides to do it

Cheers

Pavel
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Old 15-08-2011, 07:42   #3
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Re: Two Questions About OpenCPN

I find it interesting that this is of use to pilots. I've had a lot of pilots come aboard my warship, and even navigating in the extremely confined waters of the Saint Lawrence never have I seen any of them bring RTK-enabled GPS. Often we'll be in range of differential signals, and sometimes even WAAS, but I've never even seen RTK used.
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Old 15-08-2011, 08:14   #4
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Re: Two Questions About OpenCPN

Is this RTK service similar/same as Furgro Seastar XP and HP clock and carrier phase difference measurment. If it is, I cannot see any use in a pilotage situation, the movement of the vessel alone negates the quoted centi-meter accuracy.
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Old 16-08-2011, 00:03   #5
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Re: Two Questions About OpenCPN

Why are many people so hung up about metre, centimetre, millimetre, accuracy when it just isn't needed for navigation?

If you are down to needing such accuracy; you should be outside on the wheel and not even looking at the plotter. The 10m or so that GPS typically gives these days is more than enough accuracy to get you to where you need to go. The charts in most of the world are much less accurate than that even when corrected for datum, spheroid, etc..

I have seen chart errors, when referred to GPS, of more than half a mile and I know there are bigger variances out there. In one case the GPS position on a chart moved from having a large (quarter mile or so) error to the east at its eastern margin to a similar error west at the western margin. This chart covered about 15 miles. The same data as the paper chart is in C-MAP, Navionics electronic charts etc.. But the the chart is perfectly usable for pilotage - again get your head outside and off the screens when in close.

I have a photo of the plotter screen tiled with radar showing a smiliar offset which I'll dig out and post one day.

Ships use extreme accuracy at times, for docking etc.. but they are not going to be using opencpn but dedicated systems with a whole array of sensors, GPS of which is only a part.
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Old 16-08-2011, 01:17   #6
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Re: Two Questions About OpenCPN

Hi smart,

As the others mentioned, RTK is in the GPS. The chart plotter just gets the end result from the data cable. Ever since they turned off Selective Availability, a regular GPS is adequate for docking a ship or pushing a barge into a lock with a large scale ENC. The important things in these tight situations are quick refresh speed and a good heading. Most pilots connect to the Pilot Port on the AIS, so they can get heading. COG is no good for docking since you need to be moving to get any accuracy, but heading will show the ship direction when standing still.

By refresh speed, I am referring to chart display speed and the refresh rate of the GPS position. Some ECDIS systems lag in these so they do not work as well for docking as a fast charting program.

<< get your head outside and off the screens when in close. >>

Good advice, but a chart plotter actually works better for docking because it gives you a birds eye view of clearances.
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Old 16-08-2011, 02:21   #7
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You have to be on a pretty big ship to need a plotter to judge clearances. I think the OpenCPN market is aimed at the sub 24m category of vessel and for this the head outside us much better than instrument fixation.
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Old 17-08-2011, 01:23   #8
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Re: Two Questions About OpenCPN

Quote:
Originally Posted by Littlechay View Post
You have to be on a pretty big ship to need a plotter to judge clearances. I think the OpenCPN market is aimed at the sub 24m category of vessel and for this the head outside us much better than instrument fixation.
Fully agree. My work boat is 80m in length, and all docking, manoeuvering is done by eye ball.
We have the facility for RTK, never used it, the vessel is DP2 capable, but even then, wave/wind and swell will negate the centimeter accuracy. Best we can hope for if using this facility is around the 1 meter mark.

Best use eyeball, you get a much better sense as to whats happening about you.
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