The positive edge consensus problem of linear systems on undirected as well as directed nodal networks is studied here. The authors first present a distributed observer-based positive edge consensus algorithm to address the problem. The proposed observer-based protocol has more design freedom and a general form which includes the classical Luenberger observer-based protocol as a special case. Moreover, with the help of line graph theory, they map the edge topology to the line topology such that the state of each edge in the connected networks can reach consensus. Sufficient conditions in terms of solving the Sylvester matrix equation, and the linear matrix inequalities are provided to design the proposed algorithm. Finally, a simulation example is given to verify the effectiveness of the proposed positive edge consensus protocol.