With the advent of handy Unmanned Aerial Vehicles and user-friendly software implementing automated reconstruction techniques (i.e., Structure from Motion and Multi-View Stereo), the through-water photogrammetry of shallow river/sea bottom has attracted attention as a cost-efficient and high-resolution survey technique. In this paper, its methodology and limitations are discussed with some emphasis on the effects of refraction at the water surface and its ignorance in common software packages.
We developed a portable SfM/MVS system “UAV-Map3D (UM3)”. It has two types of functions : a “simple mode” that can generate point cloud, DSM and 3D surface at high speed with a touch panel, and a “professional mode” that can build each 3D data in detail by connecting a PC, therefore UM3 is expected to be useful in various situations.
The rules for operating specifications were amended in 2020, and are now allowed to be officially used as guideline for achieving stable accuracy using UAV surveying. In general, 3D reconstruction by UAV is performed using SfM/MVS software, but to achieve high-accuracy of 3D reconstruction stably, it is desirable to have as many GCPs placed in the right position. However, arrangement of GCPs is hard work and time-consuming, and therefore it is desirable to achieve accuracy goals with fewer GCPs. This paper describes the comparison of 3D reconstruction by SfM/MVS for various GCPs arrangements using UAV test site.
Recently, in the practical inspection on inner lining of tall chimneys of plants or power stations, the movie captured by 360-degree action camera installed on drone is reviewed by engineer for screening. It reduced man-hours and increased safety than visual inspection using scaffold.
Due to the safety in operation in closed space and short life cycle in the severe environment, the drone and equipment should be small, light and low cost. The drone is operated manually without GPS-based navigation.
To improve the precision, we tried capturing 1mm resolution images of inner surface of a tall chimney 150 meter in height with single compact digital camera in two days. Photogrammetric processing using SfM/MVS delivered pointcloud, and it was developed into elevation plan view, which crucks was extracted.
Three-dimensional measurement using aerial photographs by UAV has become widespread by applying SfM/MVS software. In recent years, multi-spectral cameras including near-infrared band and thermal infrared cameras have become smaller and lighter, and can be mounted on small UAVs for aerial photography. In this paper, we will introduce an example of three-dimensional measurement from aerial images taken by a UAV equipped with a multispectral camera and a thermal infrared camera.
In recent years, it has become common in the entertainment industry to use 3D and 4D data (data with time- sequential information added to 3D data) of performers for live stage production. The emergence of various application and devices in addition to the establishment of various methods for acquisition of 4D data with color information such as Photogrammetry, Grid Pattern Projection, and Time of Flight (TOF) makes it easier for those creators without special engineering skills to use those dataset, which leads to more frequent encounter with video works made with those technologies than before.
On the other hand, real time manipulation of the 4D data with different coordinate systems and formats requires development of the special software or it needs calibration. Due to those technical difficulties, we still cannot say that it is prevailing to the broader public.
Rhizomatiks has been doing research and development of the use of the 3D and 4D data made in different methods for the stage performance since 2010.
This paper introduces practical examples of implementation and gives our future prospects as a conclusion.
The Ashio region has been devastated by past disasters. This study monitored the vegetation recovery in the Ashio area using LANDSAT time series data. We used the pre-processed LANDSAT time series data for classification by SVM and time series analysis by vegetation index and bare soil index. The SVM classification results showed that vegetation had recovered significantly in the Ashio area over a period of 36 years. The MSAVI2 was suitable for monitoring the vegetation recovery in this area. As a result of the time series analysis, we identified areas where vegetation recovery was particularly significant. Also, some areas with slope failure were identified. It was found that the vegetation recovery work carried out so far was effective. There are 27.5% of the sites where vegetation has not recovered, and monitoring needs to be continued.
UAV (Unmanned aerial vehicle)-based photogrammetry without GCP (Ground control point), which combines SfM (Structure from Motion) and RTK-UAV (i.e., UAV capable of RTK-GNSS positioning of shooting position), has been studied around the world in recent years. While some studies show that the photography method and analysis settings have large effects on survey accuracy, there are only a few such studies and it is desirable to accumulate cases. In this study, experimental data simulating 14 types of photography methods, including oblique ones, were analyzed by using Agisoft Metashape with 216 SfM settings. As a result, it was confirmed that the analysis settings in addition to the photography method have complex effects on the accuracy of SfM. In addition, the accuracy did not always improve by adding images, and the analysis settings that can obtain high accuracies differed depending on the photography method.