I have a differential equation that connects the "velocity" of a point in the FOV of a camera with the velocities of a robot's joints, that is $$\dot s=J(s) \dot q$$ where s is a vector with the $x$,$y$ coordinates of the point in the FOV, $J$ is the interaction matrix and $q$ is the vector of the joint positions. 

If I have a certain point whose velocity I am tracking and this point remains in the FOV, then $\dot s$ is well defined. But if I change this point online, that is at the time instant $t$ I have point $s_t$ and at the time instant $t+dt$ I have the point $s_{t+dt}$, then $\dot s$ is not defined.

Can I create a filter to produce a continuous variation of $\dot s$? If not, what can I do?