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nasa / XPlaneConnect

The X-Plane Communications Toolbox is a research tool used to interact with the X-Plane flight simulator
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Plane flickering in playback of a recorded flight #180

Closed ppljs closed 4 years ago

ppljs commented 4 years ago

Hello,

Sorry to bother, but I am having a problem with record/playback functions of the xpc API. When I record a flight with getPOSI and then try to play it back on the simulator without the physics engine running, the plane starts to flick in the horizontal plane by some delta less than 1 meter while moving. This flicks are small teleportations in random locations of the horizontal plane with a maximum distance of one meter of the center of the aircraft, but the mean position stays the same. This issue does not happen when the airplane continuously receives a constant position.

I think this is due to floating values having poor precision for this kind of situations where the horizontal position of the aircraft is being set by latitude and longitude in degrees.

Is there another way to receive and set the position of the aircraft? I imagine this can be solved by either receiving/sending the data in double format or by receiving/sending the position data in local Cartesian coordinates, but I could not find a way of doing this with the provided API.

Sorry again to bother with this issue and thanks a lot for this amazing API!

PS: If there is a way to do what I intend but it is not yet implemented, I would be happy to contribute to add this feature.

flick_issue_xplane

jason-watkins commented 4 years ago

Hi Paulo,

Are you using the latest release? If so, the position lat/lon/alt should be already be sent as doubles. Adding a new message type to allow setting the local position directly is certainly possible and might aid with verifying that double precision still isn't enough.

If you're interested in doing so, I'd suggest starting by reading this page on the wiki that explains how the messages are formatted. Once you understand the message format, It should be relatively easy to add a new message to the MessageHandlers class. Finally you would need to add the ability to send that message type to whichever client you are using.

ppljs commented 4 years ago

Hi Jason, Sorry for the delay. Yes I am using it the 1.3 RC5 release. Thanks a lot for the insight!

The C API is updated and sending the data as doubles as you have sad, but the Python API (that is the one I am using) is not. So I made a small modification and now it is working fine. The discretization delta of double precision values is small enough to eliminate the flickering.

The other issue that I am having now is to get the position with double precision values (now they are being sent as 4 byte floats). But I am looking at the xpcPlugin and it appears to be easy to change it to enable the use of double precision on the MessageHandlers::HandleGetP method or to create an entire new method.

Thank you a lot for your help!

PS: I have found this comment on the getPOSI method of the C API: TODO: change this to the 64-bit lat/lon/h. So I am assuming the the right choice here is to modify the MessageHandlers::HandleGetP to send double values for latitude, longitude and altitude.

ghost commented 4 years ago

Paulo could you please provide the modifications you did to the python code? I am also getting stuttering.

ppljs commented 4 years ago

Hello, @pencey, yes, of course! I had to modify the plug-in to be able to receive the data in double format, so you will have to compile it to generate the modified plug-in too. I created a fork of this repo to make the modifications, follow this link: https://github.com/PauloLemgruberJeunon/XPlaneConnect

It is on a branch called "get_double_posi". Good luck and if you have any trouble, please, contact me :) .

ghost commented 4 years ago

That's great! Thank you!!

jason-watkins commented 4 years ago

I think this has been resolved by #202. Feel free to comment/reopen if there's still something that needs to be resolved here.