  The Pl\"{u}cker coordinate description of subspaces has been recently
discussed in the context of constant dimension subspace codes for random
networks, as well as the Schubert cell description of certain code parameters.
In this paper this classical tool is used to reformulate some standard
constructions of constant dimension codes so as to give a unified framework. A
general method of constructing non-constant dimension subspace codes with
respect to a given minimum subspace distance or minimum injection distance
among subspaces is presented. These codes may be described as the union of
constant dimension subspace codes restricted to selected Schubert cells. The
selection of these Schubert cells is based on the subset distance of tuples
corresponding to the Pl\"{u}cker coordinate matrices associated with the
subspaces contained in the respective Schubert cells. In this context, it is
shown that a recent construction of non-constant dimension Ferrers-diagram
rank-metric subspace codes (Khaleghi and Kschischang) is subsumed in the
present framework.
