Ad hoc network is an autonomous system that does not require a pre-established infrastructure. Nodes in ad hoc networks are connected by wireless links, and the communications between nodes are often achieved by multi-hop links. With increased interests in mobile communications and the promise of convenient infrastructure-free communications, the development of large-scale ad hoc networks has drawn a lot of attention and has been a subject of extensive research. Geometric routing is a technique in ad hoc networks to send a packet from a source node to a destination node by repeatedly forwarding a packet to an appropriately chosen neighbor node. Geometric routing finds a route by using the location of the destination node and local location information, i.e., the locations of a current node and its neighbors, and does not require the knowledge of the entire network. We give a unified view to greedy geometric routing algorithms in ad hoc networks. For this, we first present a general form of greedy routing algorithm using a class of objective functions which are invariant under congruent transformations of a point set. We show that several known greedy routing algorithms such as Greedy Routing, Compass Routing can be regarded as special cases of the generalized greedy routing algorithm.