  Ground Penetrating Radar (GPR) is widely used as a non-destructive approach
to estimate buried utilities. When the GPR's detecting direction is
perpendicular to a pipeline, a hyperbolic characteristic would be formed on the
GPR B-scan image. However, in real-world applications, the direction of
pipelines on the existing pipeline map could be inaccurate, and it is hard to
ensure the moving direction of GPR to be actually perpendicular to underground
pipelines. In this paper, a novel model is proposed to estimate the direction
and radius of pipeline and revise the existing pipeline map from GPR B-scan
images. The model consists of two parts: GPR B-scan image processing and
Ellipse Iterative Inversion Algorithm (EIIA). Firstly, the GPR B-scan image is
processed with downward-opening point set extracted. The obtained point set is
then iteratively inverted to the elliptical cross section of the buried
pipeline, which is caused by the angle between the GPR's detecting direction
and the pipeline's direction. By minimizing the sum of the algebraic distances
from the extracted point set to the inverted ellipse, the most likely
pipeline's direction and radius are determined. Experiments on real-world
datasets are conducted, and the results demonstrate the effectiveness of the
method.
