After all flights are completed, perform a preliminary data analysis and obtain precise photo centers in the local coordinate system for further processing in any photogrammetric software.
- First, organize the data:
Download all photos from the memory card to your computer and group them into separate folders by flight. The number of folders must match the number of flights.
If your TOPODRONE P24 camera is mounted on a 3-axis gimbal, download the UBX measurement files from the MicroSD card installed in the TOPODRONE UAV PPK UPGRADE KIT GNSS receiver. If your TOPODRONE P24 camera is installed together with a TOPODRONE laser scanner, use the UBX files recorded by the laser scanner.
The number of UBX files corresponds to the number of GNSS receiver initializations. The number of folders should match the number of flights and UBX files. A UBX file for a 15-20 minute flight is about 20-30 MB.
Next, download the data from your base station, convert it to RINEX and move it to a separate folder.
It is also recommended to put all information on control points and base station coordinates in a separate folder.
At this stage, it is recommended to use the structure shown in the figure below - Open TOPODRONE Post Processing and go to the PPK Post Processing module. Then proceed in order.
Images folder: the folder with photos from one flight; click Select and specify the first folder with photos.
GNSS file: specify the raw UBX measurement file created during the first flight. If all UBX files were placed in the corresponding folders when sorting the data, the UBX file loads automatically when the photo folder is selected.
Output folder: created automatically in the photo folder; can be changed if necessary.
The button next to the GNSS file opens the RTKPLOT window, where you can assess the GNSS signal quality, satellite tracks and signal-to-noise level during camera operation.
All photos taken after the drone was switched on must take part in post-processing, even those taken accidentally on the ground, provided that the TOPODRONE UAV PPK KIT receiver was successfully initialized. - Next, select the TOPODRONE P24 camera installation type from the drop-down list. TOPODRONE P24+PPK+DJI Matrice 300 is the camera on a 3-axis gimbal, and TOPODRONE P24/P61+LiDAR HI-RES/LITE/ULTRA+DJI Matrice 300 is the installation together with a TOPODRONE laser scanner. If your TOPODRONE P24 camera has a non-standard installation, the offsets of the sensor center relative to the GNSS antenna will be different and must be specified: click «Presets», enter a name and the required offsets. Click «Save», and the offsets appear in the drop-down list.
- At this stage, add the base station measurement file: click «Select» and choose the base station file. For more on the base station, see «Setting up the base station»
- After the data is loaded, the «Logs» window shows the following information: the number of photos and events, the start and end time of recording on the drone and on the base station.
The base station recording must cover the entire drone operating time. - If necessary, select the coordinate system. You can specify the height type: from projection, ellipsoidal or geoid model. In the «Projection» field, enter the name of the coordinate system or the EPSG code and select the required system in the search results.
- Then specify the precise coordinates of the base station.
For the antenna height, enter the height of the tripod or pole and add the phase center height of the GNSS receiver used. - TOPODRONE Post Processing can batch-process several flights from one base station and obtain precise photo center coordinates for all of them. To do this, in «1. Drone files» click the button, add all flights in the window that opens and click «OK»
- After completing all steps, on the «5. Processing» tab click «Start»
- The result of processing is a catalog of precise photo center coordinates in the OUTPUT folder, next to the photos of the given flight.
If all steps were done correctly, after aerial triangulation in photogrammetric software you will get an accuracy within 2-3 GSD; otherwise, check everything step by step, including the base station and control point coordinates. If the error cannot be found, contact TOPODRONE technical support. For photogrammetric processing, refer to the user manual of the software you use.