The data used in the following example was collected during the PANGAEA-X 2017 ESA led field campaign in November 2017 on Lanzarote, Spain. During the course of the campaign, over the course of 2 days, 14 photogrammetric datasets have been collected using a standard off-the-shelf DJI Phantom 4 drone \cite{ever} . The sampling site was the Tinguaton area located in Southern Lanzarote. Figure ... shows the location of the site on Lanzarote and Figure ... shows the corresponding overlay of the sampled area. Further specifications of the drone can be obtained from the DJI website \cite{downloads} or by using the DJI Phantom 4 manual \cite{manual}.A RTK GNSS system was employed to improve accuracy of the data as discussed in Section ... . Here an EMLID Reach RS \cite{controller} was used as base station in conjunction with an EMLID Reach \cite{mapping} as rover module. The set-up of the base station follows the basic guidelines as discussed in Section ... and can be seen in Figure. The rover module set-up was not as sophisticated but still followed the most basic principles. The use of a monopod instead of tripod added a slight error to the measurements as the device was more or less handheld. The set-up can be seen in Figure ... If a tripod can be obtained and portability is not a critical factor it is definitely advised to use a tripod instead.
Figures ... - ... display the settings that were used during data collection in the Field as set in the ReachView. For all possible options please refer to Section ... .
Once the RTK data was downloaded from the devices post-processing began, as we, most of the time, didn't establish a direct connection between the rover and the base. To post-process the RTK data the corresponding EMLID developed software, RTKLIB, was used. It is a free software available for Windows, Mac and Linux and can be obtained from \cite{docs}. To process the data:
RTKCONV
- Open the RTKCONV application.
- Add the rover raw log in the very first field and choose the output directory.
- Choose the format in the drop-down menu: If obtained from each rover use u-blox, otherwise RTCM3 if both were obtained from the rover.
- Open the 'Options'
- Ensure that the Version is set to 3.03 (Actual Version)
- Click the needed satellites. This depends on your location. For our data we excluded QZSS and BEIDOU.
- Click 'OK' and 'Convert' in the main window.
- Repeat the procedure with the base log.
RTKPOST
- Open the RTKPOST application.
- Choose the rover .obs file for the 'RINEX OBS: Rover field'.
- Choose the base station .obs file for the 'RINEX OBS: Base Station field'.
- You can add .nav file from the rover in the third field.
- Specify the output directory.
- Open the 'Options'.
- Choose your needed positioning mode, in our case 'Kinematic'.
- Set the 'Elevation Mask'. Usually between 15 - 20°.
- Activate 'Rec Dynamics' to estimate rover velocity and acceleration. As we used 'Kinematic' as 'Positioning Mode'.
- As before, select the used navigation systems.
- Switch to 'Setting 2'
- Switch 'Integer Ambiguity Res' to 'Fix and Hold'.
- Switch to 'Positions' tab.
- Under 'Base Station' choose either 'Average of Single Position' for any log to average single point solution or use approximate position in the RINEX .obs header by choosing 'Rinex Header Position'.
- Press 'OK' and 'Execute' in the main window.
- Two .pos files should appear in your output folder after the process is completed.
RTKPLOT
- Open the RTKPLOT application.
- You can either drag and drop the .pos file or open it by clicking on 'File', 'Open Solution-1' and choosing the .pos file.
- Green points display a fix solution, orange float, and red single solutions.
- Click on 'Show Track Point' in the toolbar to select an individual point
- Look for aggregates of points and select the middle. These are the points we surveyed.
- Look at the timestamps in the bottom-left corner and use this information to extract the post-processed GPS coordinates for your survey from the .pos file (Use a simple text editor to view it).
- Past the exact information in a new text file. I advise using a similar format as the one in Figure ...
- Plot the extracted GPS coordinates using your desired GIS software.
- Add the ESRI Shapefile obtained from the 'Survey' section on ReachView from the Rover.
- Correlate the two and give them indicative names. I advise looking for the highest resolution base map possible. This will make identification during Agisoft PhotoScan post-processing easier.