collision avoidance

i am building a robotic golf ball retriever for a golf driving range. the navigation is by gps and magnetic compass. i need a way to detect flags placed at various spots on the range. the flag staffs are about 1/2" diam and around 7’ tall. lidar? sonar? ??

i2c, serial, usb, or any common interface is ok.

Can you rely on ultrasonic signals reflecting from the flag itself? (the staff is too small).

Else you’re into image recognition and $$$$ and complexity.

I don’t think your goal is achievable without special balls (colors, or, as exist, RFID embedded $$$ balls).

How much would i have to increase the diameter of the shaft? -I could place a sleeve over the shaft. I always have the option to map the flags to be avoided but they are moved frequently and mapping would be a pain.

Ultrasonic sonar rangers will work with 0.5 inch diameter pipes, up to a couple of meters distance. You will need to experiment.

bushmaster:
How much would i have to increase the diameter of the shaft? -I could place a sleeve over the shaft. I always have the option to map the flags to be avoided but they are moved frequently and mapping would be a pain.

Don't the apps for tablets and phones used by amateur players have a database they go to that provides graphical depictions of the pin and tee placements each day?