11:00 AM - 1:00 PM
[SVC30-P05] Improving the accuracy and speed of the terrain model using UAV - case study of the lava flow of the 1986 eruption at Izu-Oshima Volcano -
Keywords:UAV, active volcano, SfM/MVS
1. Introduction
It is known that setting a reference point (GCP: Ground Control Point) is important for improving accuracy when creating a terrain model using SfM / MVS. However, it is difficult to enter the area around the crater during an eruption, and it is practically difficult to set a reference point.
The accuracy of the terrain model without a reference point was verified by combining the RTK-GNSS-equipped UAV (DJI PHANTOM 4 RTK) and D-RTK 2 (high-precision GNSS mobile station). DJI Terra was used as the terrain modeling software. In addition, DJI Terra has a real-time mapping function that makes it possible to create a terrain model during UAV flight (during shooting). In terms of speeding up, we verified this function.
In this study, the eruption made it impossible to enter the vicinity of the crater, and even in cases where the topography around the crater changed significantly and the existing reference point was lost, the position and distortion were not corrected. , We examined the measurement method for creating a topographic model assuming that the difference is calculated quickly and the amount of eruption is calculated.
2. On-site demonstration experiment
A demonstration experiment was conducted on Izu Oshima from January 17th to 19th, 2022. The UAV used was DJI PHANTOM 4 RTK. The target range was the lava flow of the 1986 eruption (Fig.1). The number of captured images is 135.
By installing the D-RTK 2 at a reference point (where the coordinates can be grasped with high accuracy) that can be seen from the site, correction data is sent to the UAV in real time based on the signal from GNSS, and positioning data is generated. Real-time correction is possible. A highly accurate terrain model can be created without a reference point.
3. Create a terrain model with DJI Terra
The processing time when processing 135 images (resolution: 5472 x 3648) with DJI Terra was about 5 minutes in the high resolution mode (full: processing with the resolution of the acquired image). Compared to other software, there are fewer operation procedures and shorter processing time, so it was found that using DJI Terra is effective in terms of speeding up.
4. Real-time mapping with DJI Terra
DJI Terra has a real-time mapping feature that creates a terrain model during flight (during shooting). In real-time mapping, the image resolution is lowered and data is transferred from the UAV to the PC containing DJI Terra, giving priority to processing speed and creating a terrain model. In fact, we photographed a lava flow about 600 m away from the takeoff position and confirmed that a terrain model was created in real time from the location where the data was transferred during the flight. The image resolution was reduced from 5472 x 3648 to 960 x 640, and a terrain model was created.
5. Accuracy verification
The difference between the terrain model created without GCP this time and the terrain model created by taking a picture with Matrice 210 in 2020 and correcting the reference point by post-processing was performed (Fig.2). Although there are differences in equipment and shooting conditions, it was confirmed that by combining DJI PHANTOM 4 RTK and D-RTK 2, the difference in accuracy is small compared to with GCP, and it is possible to create a terrain model with sufficient accuracy (Fig.3).
6. Summary
By combining DJI PHANTOM 4 RTK and D-RTK 2, it was possible to create a terrain model with high position accuracy without GCP. The maximum flight time of the DJI PHANTOM 4 RTK is 30 minutes, and considering shooting from outside the restricted access at the time of the eruption, it is possible that the range that can be shot in one flight is small. This time, it was found that using the RTK-GNSS-equipped UAV is important for creating a terrain model, so a more accurate terrain model can be shortened with the RTK-GNSS-equipped UAV capable of long-distance flight in mind. I would like to proceed with the examination so that it can be created in time.
This research was conducted as part of the Ministry of Education, Culture, Sports, Science and Technology's next-generation volcano research and human resource development comprehensive project.
It is known that setting a reference point (GCP: Ground Control Point) is important for improving accuracy when creating a terrain model using SfM / MVS. However, it is difficult to enter the area around the crater during an eruption, and it is practically difficult to set a reference point.
The accuracy of the terrain model without a reference point was verified by combining the RTK-GNSS-equipped UAV (DJI PHANTOM 4 RTK) and D-RTK 2 (high-precision GNSS mobile station). DJI Terra was used as the terrain modeling software. In addition, DJI Terra has a real-time mapping function that makes it possible to create a terrain model during UAV flight (during shooting). In terms of speeding up, we verified this function.
In this study, the eruption made it impossible to enter the vicinity of the crater, and even in cases where the topography around the crater changed significantly and the existing reference point was lost, the position and distortion were not corrected. , We examined the measurement method for creating a topographic model assuming that the difference is calculated quickly and the amount of eruption is calculated.
2. On-site demonstration experiment
A demonstration experiment was conducted on Izu Oshima from January 17th to 19th, 2022. The UAV used was DJI PHANTOM 4 RTK. The target range was the lava flow of the 1986 eruption (Fig.1). The number of captured images is 135.
By installing the D-RTK 2 at a reference point (where the coordinates can be grasped with high accuracy) that can be seen from the site, correction data is sent to the UAV in real time based on the signal from GNSS, and positioning data is generated. Real-time correction is possible. A highly accurate terrain model can be created without a reference point.
3. Create a terrain model with DJI Terra
The processing time when processing 135 images (resolution: 5472 x 3648) with DJI Terra was about 5 minutes in the high resolution mode (full: processing with the resolution of the acquired image). Compared to other software, there are fewer operation procedures and shorter processing time, so it was found that using DJI Terra is effective in terms of speeding up.
4. Real-time mapping with DJI Terra
DJI Terra has a real-time mapping feature that creates a terrain model during flight (during shooting). In real-time mapping, the image resolution is lowered and data is transferred from the UAV to the PC containing DJI Terra, giving priority to processing speed and creating a terrain model. In fact, we photographed a lava flow about 600 m away from the takeoff position and confirmed that a terrain model was created in real time from the location where the data was transferred during the flight. The image resolution was reduced from 5472 x 3648 to 960 x 640, and a terrain model was created.
5. Accuracy verification
The difference between the terrain model created without GCP this time and the terrain model created by taking a picture with Matrice 210 in 2020 and correcting the reference point by post-processing was performed (Fig.2). Although there are differences in equipment and shooting conditions, it was confirmed that by combining DJI PHANTOM 4 RTK and D-RTK 2, the difference in accuracy is small compared to with GCP, and it is possible to create a terrain model with sufficient accuracy (Fig.3).
6. Summary
By combining DJI PHANTOM 4 RTK and D-RTK 2, it was possible to create a terrain model with high position accuracy without GCP. The maximum flight time of the DJI PHANTOM 4 RTK is 30 minutes, and considering shooting from outside the restricted access at the time of the eruption, it is possible that the range that can be shot in one flight is small. This time, it was found that using the RTK-GNSS-equipped UAV is important for creating a terrain model, so a more accurate terrain model can be shortened with the RTK-GNSS-equipped UAV capable of long-distance flight in mind. I would like to proceed with the examination so that it can be created in time.
This research was conducted as part of the Ministry of Education, Culture, Sports, Science and Technology's next-generation volcano research and human resource development comprehensive project.