A Post-Scan Point Cloud Colorization Method for Cultural Heritage Documentation

Ting On Chan,Tingting Chen,Yeran Sun,Wei Lang,Lixin Liu,Ming Ho Li,Hang Xiao

doi:10.3390/ijgi10110737

Ting On Chan, Tingting Chen + Show 5 more

Open Access

https://doi.org/10.3390/ijgi10110737

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Abstract

The 3D laser scanning technique is important for cultural heritage documentation. The laser itself normally does not carry any color information, so it usually requires an embedded camera system to colorize the point cloud. However, when the embedded camera system fails to perform properly under some external interferences, a post-scan colorization method is always desired to improve the point cloud visuality. This paper presents a simple but efficient point cloud colorization method based on a point-to-pixel orthogonal projection under an assumption that the orthogonal and perspective projections can produce similar effects for a planar feature as long as the target-to-camera distance is relatively short (within several meters). This assumption was verified by a simulation experiment, and the results show that only approximately 5% of colorization error was found at a target-to-camera distance of 3 m. The method was further verified with two real datasets collected for the cultural heritage documentation. The results showed that the visuality of the point clouds for two giant historical buildings had been greatly improved after applying the proposed method.

Highlights

The three-dimensional (3D) laser scanning, commonly known as the terrestrial light detection and ranging (LiDAR), is nowadays an important technology for cultural heritage documentation [1]
We proposed a simple but efficient point cloud colorization method to perform post-scan colorization for planar features with some images acquired independently from the colorless scans obtained for dark rooms or rooms with vast occlusions inside historical buildings
It can be seen that the colorized point clouds appear almost the same as the original point cloud at the T-C distance of 3 m

Summary

Introduction

The three-dimensional (3D) laser scanning, commonly known as the terrestrial light detection and ranging (LiDAR), is nowadays an important technology for cultural heritage documentation [1]. The scanner comprises a laser component that emits and receives laser signals, along with measurements collected from digital angle decoders, to generate a cloud of 3D coordinates (point cloud) of a target. Neither mode of the laser loads a color-related information or color model (e.g., the red, green and blue model) but only a returned-laser intensity. Many terrestrial scanners are embedded with a digital camera, which provides colors to every single point in the point clouds. This is one of the most common colorization methods adopted by the current commercialized laser scanners [2]. As colors are important components of culture and architecture, point

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Results

Conclusion