WingtraOne PPK—Swiss coordinate systems

WingtraOne PPK by default gives data in WGS84 with ellipsoidal height. However, for surveying applications, local coordinate systems are usually used. 

The figure below illustrates the workflow with coordinate systems and WingtraOne PPK.

 

WiH_CoordinateSystemOverview

In the following, the optional coordinate conversion of WingtraOne PPK aerial data to local projected Swiss coordinates CH1903+/LV95 with LN02 (height reference) is detailed.

Basically, after WingtraHub PPK processing, another coordinate conversion has to be applied, which deviates from the default setup.

Swiss_coordinates

Step by step instructions

1. The base station location is provided by the CORS network swipos and is given in the  CHTRF95/ETRF93 coordinate system, which is a geographic Earth-centered and Earth-fixed. Since it is ITRF-based, these coordinates can be used directly in WingtraHub as a base location.

2. Define CSV file type in WingtraHub settings as Agisoft Photoscan type (even if using Pix4Dmapper).

3. Define the base station location in WingtraHub. For clarity, indicate the coordinate system you are using with the base station name. In Switzerland, we recommend to use CHTRF95/ETRF93 delivered by swipos. As visualized in the flow chart above, the image geotags will refer to the same coordinate system as the base station, in this case CHTRF95/ETRF93, while the altitude will be ellipsoidal. To save space and avoid errors we recommend using the option "CSV file only."

4. Open the *.csv file in the OUTPUT folder of your WingtraPilot project folder and remove the orientation information to find four columns with "filename, longitude, latitude, altitude" in decimal degrees (and m for the altitude).

5. Load the .csv file to REFRAME in order to transform the horizontal coordinates to the CH1903+/LV95 system and the altitudes to the LN02 datum. Setup the conversion as indicated in the screenshot below:

 

CS_Swiss_Reframe

6. Download the converted *.csv file and save it to the OUTPUT folder of your WingtraPilot project. Each image geolocation in the *.csv file has CH1903+/LV95 as coordinates and LN02 as a height reference.

7. In your post-processing software, import the images.

8. Import the converted .csv to load the image geolocation.

9. Define image geolocation accuracy of all images using the accuracy values specified in the WingtraHub processing report, which you can find in the OUTPUT folder of your project folder.

10. Define the image / input coordinate system. Make sure to select CH1903+/LV95 as horizontal and LN02 as vertical coordinate system. In Pix4Dmapper select vertical coordinate system: "Arbitrary," since LN02 is not an available option.

11. Define the output coordinate system to CH1903+/LV95 for the horizontal and LN02 for the vertical coordinate system. In Pix4Dmapper select the vertical coordinate system: "Arbitrary", then it will maintain the image coordinate system.

12. Process the project and verify the results using check points defined in CH1903+/LV95 LN02.