UAS 영상기반 문화유산물의 정밀 3차원 현상 모델링

The Precise Three Dimensional Phenomenon Modeling of the Cultural Heritage based on UAS Imagery

Abstract

컴퓨터기술의 발달, 영상해석 기술의 고도화 및 경량 무인항공기(UAV)가 대중화되면서 'UAV와 각종 센서의 융합을 기반으로 한 응용시스템(UAS)'이 산업계 전반으로 확산되고 있다. 국가문화유산물의 기록, 유지 관리는 물론 파손 시 복구를 위해서는 효율적인 정밀 3차원 현상 모델링 재현과 주기적 육안점검 기술이 필요하다. 본 연구의 목적은 초대형 마애보살입상의 정밀 현상모델링 재현과 육안점검의 대안으로 UAS 영상을 기반으로 한 사진측량방법의 효용성을 검증하는 것이다. 이를 위해 고려시대(918-1392) 제작된 국내 최대 마애불이며 당초문양의 '보관(모자)'이 특징인 보물 제1324호, 시흥 소래산 마애보살입상을 대상으로 UAS 영상을 획득하고 검사점에 대한 UAS 영상해석과 토탈스테이션 측량시스템 간의 측위정확도를 비교하였다. 또한, 실세계좌표계 상의 3차원 현상모델링 및 선각 현상을 도화하여 문화재청의 정량적 규격 값과 비교하며 유지관리를 위한 육안점검 작업의 대체 가능성을 검토하였다. 특히, UAS 영상해석과 지상 레이저 스캐너에 의한 3차원 재현 모형간의 중첩해석을 통해 두 기법간의 활용성은 물론 2년 전 후의 상대적 변동 상태를 검토하였다. 연구결과, 대형 마애보살입상의 정밀 현상조사 및 육안점검의 대안으로 UAS 영상 해석법의 효용성을 확인할 수 있었으므로 향후, 대형 국가문화유산의 현상조사와 유지관리에 그 활용이 기대된다.

Recently, thank to the popularization of light-weight drone through the significant developments in computer technologies as well as the advanced automated procedures in photogrammetry, Unmanned Aircraft Systems have led to a growing interest in industry as a whole. Documentation, maintenance, and restoration projects of large scaled cultural property would required accurate 3D phenomenon modeling and efficient visual inspection methods. The object of this study verify on the accuracies achieved of 3D phenomenon reconstruction as well as on the validity of the preservation, maintenance and restoration of large scaled cultural property by UAS photogrammetry. The test object is cltural heritage(treasure 1324) that is the rock-carved standing Bodhisattva in Soraesan Mountain, Siheung, documented in Goryeo Period(918-1392). This standing Bodhisattva has of particular interests since it's size is largest stone Buddha carved in a rock wall and is wearing a lotus shaped crown that is decorated with arabesque patterns. The positioning accuracy of UAS photogrammetry were compared with non-target total station survey results on the check points after creating 3D phenomenal models in real world coordinates system from photos, and also the quantified informations documented by Culture Heritage Administration were compared with UAS on the bodhisattva image of thin lines. Especially, tests the validity of UAS photogrammetry as a alternative method of visual inspection methods. In particular, we examined the effectiveness of the two techniques as well as the relative fluctuation of rock surface for about 2 years through superposition analysis of 3D points cloud models produced by both UAS image analysis and ground laser scanning techniques. Comparison studies and experimental results prove the accuracy and efficient of UAS photogrammetry in 3D phenomenon modeling, maintenance and restoration for various large-sized Cultural Heritage.

Figure 1. Illustration scheme of the pinhole camera model (a) and of the epipolar geometry (b)

Figure 2. Diagrammatic representation of the parameters for triangulation principle of Laser Scanner system with Camera

Figure 4. The location of the UAS shooting points, the 3D reproduction model based on SfM image analysis using both the control points on the rock-carved Bodhisattva and the images acquired on (a) December 2, 2016 and (b) November 16, 2018, respectively.

Figure 7. Comparison of matching status for overlaid parts between 3D points cloud models of the rock-carved Bodhisattva reconstructed by both UAS photogrammetry surveying and TLS Surveying over about two years ago and after.

Figure 8. The reconstruction of the rock-carved Bodhisattva by Rubbing, TLS, and UAS image, and UAS-based drawing reproduction of the intaglio line

Table 1. Comparison of quantitative size for the major parts of the rock-carved Bodhisattva between UAS Image based reconstruction model and existing presentation materials

Figure 9. The UAS image-based front and right sides of the rock-carved Bodhisattva. In addition, The magnification image of the normal line (the maximum distance deviation) constructed at the inflection point by the slope line connecting the top of the hat and the bottom of the pedestal.

Figure 10. Structural characteristics of rock wall surface, reinforcement facility of drainage at the upper rock wall, and facilities around rock wall for maintenance of the rock-carved Bodhisattva.

Figure 3. (a) GNSS surveying for ground control point's coordinate determination, (b) Non_prism total station surveying for coordinates determination of the natural and artificial points on the rock-carved Bodhisattva, (c) shape of artificial target, and (d) UAS photographing for reconstruction of Bodhisattva.

Figure 5. (a)Terrestrial laser scanning by SX10 TLS surveying, (b)the whole view of the rock around the Bodhisattva with SX10 TLS stations, and (c)detail of points clouds of Bodhisattva.

Figure 6. (a) Distribution of the artificial control points and natural check points on the rock-carved Bodhisattva, (b) detail of check points, and (c) comparison of 3D coordinates between the reconstructed Bodhisattva's model and non-prism total station for 3D geometric accuracy verification