How do you set the home position to fly with optical flow navigation?

PX4 Autopilot Configuration and Flight Modes
#1

Hi. I am complete unable to fly with optical flow navigation. The same problem always arises, that there is not home position set.
How are you able to set this home position?
Or, alternative, is there any way to go about this issue?
I am currently trying to fly the iris_opt_flow model in SITL and it is completely imposible.

Please, any help would be so welcome.
Thank you!

#2

What flow sensors are you using?
Did you turn off GPS?

#3

For visual navigation I am using lidar + px4flow (the ones in the iris_opt_flow model).
GPS is indeed OFF.

#4

Ok, well you can not “navigate” with lidar.
How would you expect that the distance from something will give you a position? The lidar has no way to know what that distance is from. If it is pointing down it would be your altitude, but you need at least 3 coordinates for a position. Can work for a more actuate altitude, and obstacle detection but not position.

#5

I said I am using visual navigation via lidar and px4flow. Not just lidar.
Besides, the iris_opt_flow is a complete model that includes IMU and other sensors. I did not create the model, it is an existing one.

#6

@Xun An optical flow sensor outputs velocity measurements and not position. Therefore the position will eventually drift and you cannot “visually navigate” with only optical flow without GPS.

#7

How is it done for indoors flying then when GPS is not available? @Jaeyoung-Lim

#8

Hi again @Jaeyoung-Lim. Is it no specified here: Optical Flow | PX4 User Guide that Optical Flow can be used for indoors navigation? If so, I don’t understand how you cannot navigate via optical flow without GPS.

#9

@Xun I don’t think the documentation mentions anything about indoor navigation.

Flying indoors and navigating indoors are two different topics.

You can fly manually (e.g. position mode) so that the vehicle stays in one place and you can command stick inputs. Optical flow sensors are helpful for this use case since the velocity information is useful for stabilizing the drone

Navigating means that you can specify goals that the vehicle is supposed to reach. Since you cannot estimate the position with velocity information, you cannot navigate through indoor environments with just an optical flow.

For indoor navigation, normally a vision based positioning system is used which can estimate your position through camera data.

Hope this answer is helpful

1 Like
#10

Thank you @Jaeyoung-Lim. Indeed, your answer is very helpful. Just for reassurance, VIO would be an option for GPS-less navigation, correct?