i think it's possible only when the information of the ground is well known。

I think, you must first equip every leg in proximity sensor.

Article Experimental construction of walking robot

I think it depends on the degree of freedom of your legs and the possible range of each joint. Depending on the system it could be possible to reverse calculate possible body attitudes based on these constraints. It did something similar with the human hand, but it has the "advantage" of higher dependencies between the joints.

For body attitude (roll, piach & yaw) I using IMU sensor.