playback VDR from recorded file

[skipperearly]

Have recorded a recent trip and want to playback route now with faster speed.
When doing so the SOG shown in the dashboard becomes meaningless rather than showing the original SOG.

Want to check here if others have same behavior before I raise a bug report.

[rgleason]

Under Dashboard preferences > appearance, what do you have for settings for
Cog damping factor and Speed over Ground damping factor?

[nohal]

Originally Posted by skipperearly

Have recorded a recent trip and want to playback route now with faster speed.
When doing so the SOG shown in the dashboard becomes meaningless rather than showing the original SOG.

Want to check here if others have same behavior before I raise a bug report.

You want to fill a bug report for what exactly (= what is "meaningless" in the context of your post)? Remember that when you play the VDR data, you simulate data flow from the actual sensors - while playing at 10x the original speed at which it was recorded, your position changes 10x faster and your resulting SOG is obviously something like 10x higher than it actually was.

[skipperearly]

@rgleason: SOG damping 40, COG damping 15

@nohal: well maybe the objective of the pi is not as I expected. I was expecting that when I record in VDR all available data are recorded (I noticed even AIS data are recorded - which BTW I find great for proof in case needed !) - so following this logic I had expected the "real" SOG to be recorded. To play the file faster or slower should not make any changes to the SOG - similar to when you fast forward a video you also do not show the actual time but the time of the original video.

.. if the current behavior is as required by design and not a bug but a feature to create virtual SOG's then I propose to raise it as a feature request

[Paul Elliott]

Originally Posted by nohal

Remember that when you play the VDR data, you simulate data flow from the actual sensors - while playing at 10x the original speed at which it was recorded, your position changes 10x faster and your resulting SOG is obviously something like 10x higher than it actually was.

Is the VDR playback calculating SOG from the difference in GPS positions and using the realtime computer clock? I don't think it should, rather, it should be using the SOG as given by the GPS RMC sentence or similar data. In this case the displayed SOG should be identical to the original SOG. At least that's now NavMonPc does it.

If somehow the SOG is re-calculated based on the playback speed-up, then wouldn't the wind speed / angle also need to be recalculated? And why would any of this be useful?

[nohal]

Originally Posted by Paul Elliott

Is the VDR playback calculating SOG from the difference in GPS positions and using the realtime computer clock? I don't think it should, rather, it should be using the SOG as given by the GPS RMC sentence or similar data. In this case the displayed SOG should be identical to the original SOG. At least that's now NavMonPc does it.

If somehow the SOG is re-calculated based on the playback speed-up, then wouldn't the wind speed / angle also need to be recalculated? And why would any of this be useful?

VDR playback does not recalculate anything.
An instrument designed to calculate speed from change of position over time of course is affected by the playback speed, which "simulates" bigger change in position over shorter time.
Wind speed has absolutely nothing to do with speed of playback, position change and time.

[Paul Elliott]

Originally Posted by nohal

VDR playback does not recalculate anything.
An instrument designed to calculate speed from change of position over time of course is affected by the playback speed, which "simulates" bigger change in position over shorter time.
Wind speed has absolutely nothing to do with speed of playback, position change and time.

OK, but *what* instrument is calculating the speed in this playback scenario? And shouldn't this "instrument" also be looking at the timestamps in the sped-up data?

And why wouldn't the True Wind data be affected as well? If the recalculated speed is deemed valid, then the True/Apparent wind angles should be affected as well.

Sorry, but this makes no sense to me. The speed displayed during fast playback should not be accelerated. The wind data should also be unaffected. The displayed time should reflect the playback speed.

Which VDR plugin is being discussed here? I should probably install it and try it out before I get even more confused.

[nohal]

Originally Posted by Paul Elliott

OK, but *what* instrument is calculating the speed in this playback scenario? And shouldn't this "instrument" also be looking at the timestamps in the sped-up data?

And why wouldn't the True Wind data be affected as well? If the recalculated speed is deemed valid, then the True/Apparent wind angles should be affected as well.

Sorry, but this makes no sense to me. The speed displayed during fast playback should not be accelerated. The wind data should also be unaffected. The displayed time should reflect the playback speed.

Which VDR plugin is being discussed here? I should probably install it and try it out before I get even more confused.

https://opencpn.org/OpenCPN/plugins/vdr.html and yes, you should probably install it to see what it actually does and, more importantly, what it does not.

[Paul Elliott]

I can't get it to load. I'm running OCPN 4.8.2, and downloaded and ran the VDR install file. I've restarted OCPN several times and can't find VDR in the list of plugins. There's no mention of VDR in the OCPN log file.

But more important, are you saying that OCPN does show an accelerated SOG when VDR is playing back logfiles at a high speed? This is what the OP reported. If so, I say it shouldn't. As a user that's not what I would want to see.

[nohal]

Originally Posted by Paul Elliott

I can't get it to load. I'm running OCPN 4.8.2, and downloaded and ran the VDR install file. I've restarted OCPN several times and can't find VDR in the list of plugins. There's no mention of VDR in the OCPN log file.

But more important, are you saying that OCPN does show an accelerated SOG when VDR is playing back logfiles at a high speed? This is what the OP reported. If so, I say it shouldn't. As a user that's not what I would want to see.

No, I am not saying anything like that, OpenCPN, where designed to show SOG as received in the NMEA stream, shows the value received, as far as I can say, even when the input comes accelerated from the VDR plugin. If it does not, it is a bug. I can not find any such place playing (BTW your) recorded data with the VDR plugin at any speed.
Where designed to calculate it from position change over time, it shows the value calculated so. This is by design for cases where SOG data from the instruments is not available or wrong and the user does not want to use it. As far as I can tell this also works as expected.
If the OP has a problem, we simply need more input to asses if it is a real problem and worth a fix or a change or not.

[rgleason]

Paul, perhaps you have multiple/parallel installs?
It should work, as I've used it a lot with 4.8.0,4.8.2 and 4.8.4 etc. Perhaps you are linux? Don't remember.
You could try this one.




PS: These are good questions. I can say as I know the answers though.

[Paul Elliott]

Originally Posted by nohal

No, I am not saying anything like that, OpenCPN, where designed to show SOG as received in the NMEA stream, shows the value received, as far as I can say, even when the input comes accelerated from the VDR plugin. If it does not, it is a bug. I can not find any such place playing (BTW your) recorded data with the VDR plugin at any speed.

Ok, I must have misunderstood your earlier post. The behavior you describe sounds very reasonable.

Where designed to calculate it from position change over time, it shows the value calculated so. This is by design for cases where SOG data from the instruments is not available or wrong and the user does not want to use it. As far as I can tell this also works as expected.
If the OP has a problem, we simply need more input to asses if it is a real problem and worth a fix or a change or not.

This part is a bit problematic. If the speed calculation does not also use the GPS timestamp (which will also be sped-up during VDR high-speed playback), I would consider that a bug. And by the same reasoning that produced the accelerated SOG, any resulting AW/TW calculations would also be affected. But someone else might reasonably disagree with me on this point. I wasn't even aware that OCPN could do its own SOG calculations.

[Paul Elliott]

Originally Posted by rgleason

Paul, perhaps you have multiple/parallel installs?
It should work, as I've used it a lot with 4.8.0,4.8.2 and 4.8.4 etc. Perhaps you are linux? Don't remember.
You could try this one.

That's the same VDR I just tried to install. It went into the "C:\Program Files (x86)\OpenCPN\plugins" directory. I'm running this on a fairly new MINIX computer, under Win10/64. It's a clean install, with no previous OCPN versions. My big, fancy, new, fast Dell PC stopped working last night so today I'm using the little MINIX -- which I got for testing.

[rgleason]

That looks like a correct installation location for a new install. I just tried the VDR_pi-0.4 installed into Opencpn v4.8.4 and v4.8.2 and they both seem to work using a small file from Hartmut which is attached.

I've also attached some screenshots of the install process and the operation of VDR.

I wonder what it is that is causing the problem. I wonder if you have a parallel install? C:\Program Files (x86)\OpenCPN 4.8.2

You'll need too remove the pdf on the harmut file and unzip.

BTW Paul, thank you for your help with posting the new sticky. It will help users find appropriate threads so that searches for answers are more effective.

[Paul Elliott]

Originally Posted by rgleason

That looks like a correct installation location for a new install. I just tried the VDR_pi-0.4 installed into Opencpn v4.8.4 and v4.8.2 and they both seem to work using a small file from Hartmut which is attached.

Thanks. I got it to work -- turns out that I had been installing my programs on a different SD-card "drive", since this MINIX computer has a tiny SSD for "C:" that barely fits Win10 by itself. I had let the VDR install itself on "C:". I moved it over to the proper drive and now it works.

And playing back one of my own logfiles shows the original SOG regardless of the playback speed. This is what I would expect.