Vision position estimate , motion capture

we have created a position system that gives x,y,z on the drone.I’m sending this postion as mavlink vision position estimate msg using dronekit python, i wanna know what param do i have to change in mission planner so that the pixhawk will use this msg instead of the gps to estimate the position

Very similar to the Intel T265, as it uses MAVLink Vision Position messages too, so use the Ardupilot settings in the Wiki: Intel RealSense T265 — Copter documentation

After reading some ardupilot thread it seems that i have to define GPS_GLOBAL_ORIGIN
HOME_POSITION, is it necessary and what does the autopilot do with it

Yes, you need to set GPS_GLOBAL_ORIGIN, as Ardupilot needs a mapping from the 0,0,0 position of your system to a longitude/latitude/altitude.

Thank you for helping me,but what about HOME_POSITION i read its for the landing approach is it necessary to set

HOME_POSITION is automatically set by ArduPilot when the vehicle is armed. You don’t need to set anything.