The combination of DroneViewer and drones makes for a powerful duo. With DroneViewer you can see exactly where your drone was on a Google Map at the time of video capture. You can GeoTag key points in your video to mark their positions on the Map and return to those points at any time. The GeoTags also display the line-of-sight (LOS) distance from the tag to the current drone position. This can be used to show your distance from the operator, as shown below:
GeoTags, shown in the Map and in GeoTags list on right, show key points of interest and distances to the UAV. In this case the tags represent the locations of the two oil rigs, Emma and Eva, which are not shown in Google Maps. The graph in the bottom-left shows the UAV speed versus time. The lower-mid Dashboard display shows the speed distance, heading, position, and number of GNSS satellites in view. The LOS distance of the drone from the operator was 1.5 miles at this point in the video.
You can then export your GeoTags to an Excel file for review and analysis. Below is another example showing DroneViewer used for post-flight examination of drone video.
Currently DroneViewer can accept GPS data from drone footage in four forms: DJI’s SRT file (Mavic Pro, Mavic Pro 2, Phantom 3,4), Autel EVO, GPX file, and FlyTrex Core 2 file. These methods are described below:
Loading movies and data
Run DroneViewer and load your drone’s movie files through the File menu or through the Open Folder, or Open Files toolbar button. DroneViewer will look for GPX, SRT (DJI), ASS (Autel) and Flytrex CSV data files in the movie file directory. In order for DroneViewer to associate the movies with the correct data files, the data files must have the same base name as the movie files. For example, DroneViewer would expect to find the file DJI_0007.GPX, DJI_0007.SRT or DJI_0007.CSV if the movie DJI_0007.MP4 was loaded.
DroneViewer will begin playing the first movie in the folder or in the list of movies that was selected. By default files are loaded according to file modification date (this can be changed to name ordering in the Preferences). When DroneViewer reaches the end of the movie it will jump to the next movie in the list and continue playing. It will do this until all movies have been played.
Importing drone flight data from a DJI SRT file
If your DJI drone is controlled by the DJI Go App or DJI Fly App, then you can easily import your flight trajectory into DroneViewer via the SRT file. Before your flight, be sure you turn on the Video Caption option in the Go or Fly App camera settings.
Turn on Video Caption in your DJI Go App settings to have your UAV create SRT files alongside your movie files
In the DJI Fly App, be sure to turn on Video Subtitles. Also, choose H.264 video encoding because H.265 (HEVC) is not supported on all devices at this time.
This will make the drone create an SRT file for each movie. The SRT file contains the flight trajectory information. Make sure the SRT file is in the same directory as your movie and has the same root name. Drag one of your movies into the DroneViewer window or select Open Movie File from the File menu. DroneViewer will process the data and you’ll see your drone’s flight path and current position as the movie plays. The speed and number of satellites-in-view are also shown in the Graphs.
A few caveats when working with SRT files:
- If you rename the movie, be sure to rename the SRT file as well or else DroneViewer will not be able to find it.
- The speed of the drone is computed based on waypoints. While it’s great that DJI conveniently logs the drone’s flight data into an SRT file, the speed of the drone is not recorded to the file and the latitude and longitude are not stored in high precision. DroneViewer uses the time-stamped lat/lon values to estimate the speed. The lack of precision means the drone speed and direction can be inaccurate and appear to vary wildly. DroneViewer applies a smoothing function to dampen the speed variations. While this helps, it’s not a perfect solution. Ideally, DJI would modify their SRT file data to include native drone speed and higher-precision latitude and longitude. (There are other ways to extract the flight data to higher-precision but they are not as convenient as the SRT file method).
Importing drone flight data from an Autel EVO ASS file
If you have an Autel Evo and use the Autel Explorer App , then you can easily import your flight trajectory into DroneViewer via the ASS file. Before your flight, be sure you turn on the Subtitle .ass Files option in the Explorer App camera settings.
Turn on “Subtitle .ass Files” in your Autel Explorer App settings to have your UAV create ASS files alongside your movie files
This will make the drone create an ASS file for each movie. The ASS file contains the flight trajectory information. Make sure the ASS file is in the same directory as your movie and has the same root name.
Drag one of your videos into the DroneViewer window or select Open Movie File from the File menu. DroneViewer will process the data and you’ll see your drone’s flight path and current position as the movie plays. The speed, distance, and altitude are also shown in the Graphs.
A few caveats when working with ASS files:
- If you rename the movie, be sure to rename the ASS file as well or else DroneViewer will not be able to find it.
- The speed of the drone is computed based on waypoints. While it’s great that Autel conveniently logs the drone’s flight data into an ASS file, the speed of the drone is not recorded to the file and (as of firmware 1.4.9) the latitude and longitude are not stored in high precision. DroneViewer uses the time-stamped lat/lon values to estimate the speed. The lack of precision means the drone speed and direction can be inaccurate and appear to vary wildly. DroneViewer applies a smoothing function to dampen the speed variations. While this helps, it’s not a perfect solution. Ideally, Autel would modify their ASS file data to include native drone speed and higher-precision latitude and longitude.
- Autel stores altitude relative to the standard WGS84 ellipsoid. Thus raw altitude values may appear as negative values even though the drone is above the earth’s surface. DroneViewer allows you to correct for this in a number of ways. For example, select the “Geoid” option in the Preferences to have DroneViewer convert the WGS84 altitude to Mean Sea Level altitude. You can also select the “relative to first point” option to have DroneViewer display the altitude relative to the first data point loaded.
- The ASS files produced by firmware v1.4.9 (which say v4.00+ at the top of the file) contain syntatic errors in the longitude position. Autel has been notified of this error and hopefully it will be recitified soon. In the mean time, DroneViewer applies workaround for this bug so your drone’s stated location should be correct. When the longitude is eventually fixed, DroneViewer should work with the corrected format as well.
Importing drone flight data from a GPX file
GPX is an XML-based navigational data exchange format consisting of tracks and waypoints. An example of a very short GPX file is shown below. This sample has one track consisting of 2 waypoints:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?> <gpx xmlns="http://www.topografix.com/GPX/1/0" version="1.0" creator="DroneViewer Pro"> <metadata> <name>Sample GPX</name> </metadata> <trk> <name>Track Start Time: 2018-01-15T00:28:00Z</name> <trkseg> <trkpt lat="33.6673000" lon="-118.0274000"> <ele>22.1</ele> <time>2018-01-15T00:30:56Z</time> <speed>15.5</speed> </trkpt> <trkpt lat="33.6674000" lon="-118.0273000"> <ele>22.0</ele> <time>2018-01-15T00:30:57Z</time> <speed>15.2</speed> </trkpt> </trkseg> </trk> </gpx>
To load a GPX file into DroneViewer, you must give it a filename with the same base name as the movie it is associated with. For example, to load GPX data for a movie named DJI_0007.MOV, you must name the GPX file DJI_0007.GPX.
If there is a timing bias between the movie and the GPX file, you can compensate for this by adjusting the Time Offset in the Preferences after loading the movie/GPX file. If you make a change to the Time Offset, be sure to de-select the Always Auto-Fix Time Offset checkbox or the offset will be forgotten when the second time the movie is played.
If manually adjusting the timeline, de-select Always Auto-Fix Time Offset.
An easier way to make the Time Offset adjustment is to use the “,” and “.” keys in the Graph window. These keys will adjust the Time Offset by -1 or +1 seconds. For coarser adjustments, the “m” and “/” keys will move the Time Offset by -10 and +10 seconds.
Adjust timeline using ‘m’, comma, period, and ‘/’ keys when the Graph view is selected. Use keypoints in the video and map to help with precise alignment.
When you are happy with the synchronization, click the Save Settings button, which looks like a disk icon in the Main window. The icon will turn green to indicate the settings, including the synchronization, have been saved.
Saving the timeline settings
A settings file will be created in the same directory as the movie file. This file is automatically loaded every time you load this movie. If you’re not happy with the synchronization, click the disk icon again to delete the settings file. Then you can try again.
Importing drone flight data from a FlyTrex Core 2 data logger CSV file
FlyTrex provides simple add-on logger that records your drone’s flight data to a microSD card. The Core 2 is compatible with many drones but I have only tested this method with the DJI Phantom 2.
- After your flight, upload your FlyTrex Core 2 data file to the FlyTrex website. Click on the arrow at the top right of the mission and select Export Mission.
- Choose the Download CSV option to export your flight data.
- Find the CSV file and drop it in the same folder as your flight movie. Rename the CSV file so it has the same base name as the movie file. For example, if your movie is called oil_pipeline.mov name the CSV file oil_pipeline.csv.
- When you load the movie into DroneViewer the GPS flight data will be loaded as well. Unlike the SRT method, you will need to adjust the synchronization of the GPS log to the video. This is due to the difference in time between when the video recording started and when the GPS log started. To override DroneViewer’s automatic syncing feature, please refer to the GPX instructions in the previous section.