Find one square meter of ground

Hi everybody,
I am completely new here.
Can anybody give me a hint how to measure 1 square meter on the ground with a normal android phone? I would like to buy a steoreo cam train a neural net (or a point cloud model) with it and then use the model.
I would like to get the information, in order to count objects lying on the ground.

Thank you very much.
Gerhard