1 Introduction
Obtaining a perspective of a wall is not just an adolescent fantasy inspired by the movie Superman. More importantly, it has great practical significance as well. Nowadays, as space efficiency and aesthetics are increasingly taken into consideration for interior design, in-wall pipeline systems for water supply and draining have become continually popular [1]. What is more, modern architects prefer reinforced concrete structures for fastness. However, inconvenience even dangers can arise when drilling through a wall for practical purposes like repairing defective pipes due to existing in-wall structures. Hitting a rebar while drilling into a wall can destroy the drill itself and severely weaken the concrete structure. In the case where an in-wall layout is unknown, repairing pipes even with just a few defects can become destructive and labour-intensive work [2]. All these add up to absolute necessity of gaining a view of in-wall structures.