Generate a polygon directly with GNSS RTK of my boat

Hello,
Sorry for my English, I french with not ggod level in English.

I like to know if it’s possible to store a polygon when I pilot boat on manual mode. And after I like use Simple grid for generate survey but it is important that the boat does not go out of the polygon because there are many obstacles outside the defined area.

More information about system:
I use 2 GNSS for Survey (bi-frequence L1/L2, GPS-GLONASS and BEIDOU)
GNSS base place on a know point and transmit RTCM3 correction directly to Rover with internal radio.
Rover on the boat send position on NMEA message on GPS1 port of my pixhawk Cube black.

I read it’s possible to store waypoint with RC commande, ok but how to generate polygon for use Simple grid fonction?

Thanks you

Ludovic

I will be accused to saying this too often, but a small plugin can do that for you automatically.
BUT If you OK with some manual text file editing then
Generate waypoints via rc commands, then download and save to file the generated waypoints.
It will look like this

QGC WPL 110
0	1	0	0	0	0	0	0	0	0	0	1
1	0	3	16	0.00000000	0.00000000	0.00000000	0.00000000	47.44550410	19.09973140	100.000000	1
2	0	3	16	0.00000000	0.00000000	0.00000000	0.00000000	47.45537110	19.11483760	100.000000	1
3	0	3	16	0.00000000	0.00000000	0.00000000	0.00000000	47.44457540	19.12839890	100.000000	1
4	0	3	16	0.00000000	0.00000000	0.00000000	0.00000000	47.43493860	19.11088940	100.000000	1

A polygon file (.poly) is looks like something like this

#saved by Mission Planner 1.3.70
47.4638436117631 19.079475402832
47.4727789016031 19.1004180908203
47.4652362243836 19.1120910644531
47.4562996522498 19.0914916992188
47.4638436117631 19.079475402832

So all you have to do is to delete the unnecessary data from the mission file and use it as a polygon file. (Tipp, use notepad++, you can select blocks to delete with alt+cursor keys…)

Thanks for your solution, it’s easier than my first test (I insert waypoint on QGIS and create Shape polygone).