Sensor to keep precise altitude and position with pixhawk

Hardware Pixhawk family
1

Hello,
i would like to build an ‘Agriculture’ hexacopter.
I bought skydroid T10 and i am going to buy pixhawk 2.4.8 as flight controller.
One of my main goals will be to set a precise altitude that should be held by the hexacopter during the operations (mainly, spreading fertilizer or herbicide)
In my agricultural fields, the ground is almost perfectly flat (levelled by laser): i would like to set an altitude, about 2 meters from the ground , and this should be held by the drone as precisely as possible.
How can i get this behaviour?
I have to buy an ultrasonic sensor? and i need some special firmware on pixhawk to manage it?

And, the second goal should be that the hexacopter should move in the XY plane following the mission path as precisely as possible.
To achieve this i need a secondary gps? or what else?

Let me know, thank you!

Lodovico

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2

Hi Lodovico @vicolodo,
For altitude control you wouldn’t want to use any ultrasonic sensors since those are not that reliable on drones because of too much noise.

For altitude control you might want to use a range finder like the LightWare products and you can read more here, I use SF11/C

For precision maneuvering you might consider looking at RTK systems
HTH
Gal

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