The active contour extraction algorithm

which uses the Gradient Vector Flow （ GVF） field as its external force

is called a GVF snake. This paper first introduces the principle of the GVF snake. Then

the role of the GVF snake’s internal and external forces

and the impact of the initial boundary on the result is investigated. After that

a reasonable solution is proposed for the GVF snake initialization and weighting parameter determination. Finally

an interactive GVF snake algorithm is designed and applied to extract irregular water boundaries from remotely-sensed images. In this algorithm

the initial boundary is acquired using the region growing algorithm based on seed pixels

and the weighting parameters are determined interactively. The real boundary is obtained using the GVF snake algorithm. The experiments show that the interactive GVF snake algorithm can extract the water boundary easily

fast and accurately

even if it is very irregular.