How to Geotag images using Dataflash logs

Hi, I have been trying to geotag images using the data flash logs downloaded from the APM, but I have not been able to get the correct locations to be tagged in the pictures. I suspect that I need to change the Log Offsets line? but I do not know the values. Can anyone tell me how this should be done? Thanks!

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      • I have previously succeeded in using such a setup very effectively on a MicroPilot system where the autopilot was triggering the camera via a servo pressing the shutter button. The camera never failed to trigger. Aerial imagery should always be shot with the focus set to infinity, which eliminates the extra delay incurred in autofocus mode. There may still be a slight delay, but most modern aerial image mosaicking solutions (e.g. Pix4D, DroneMapper, Agisoft) are able cope with that and correct for it in the process of stitching the images. Then again, if you're 100% DIY or not shooting in an overlapping mosaic pattern, I can see how that might be problematic. *But*, then again, GPS receivers have an error of several meters to begin with, so at the end of the day it's impossible to avoid a certain degree of error even when using the time offset approach. As you said: there's no perfect way.

        http://diydrones.com/forum/topics/apm-mission-planner-geotagging-to...

        http://ardupilot.com/forum/viewtopic.php?f=12&t=6629

  • Hi Jaime,

    I have a few questions about your question.

    1.) Is this basically an alternative to using a camera with a built in GPS? 

    2.) Do you know whether this is a more accurate method for photogrammetry? 

    3.)  After finding the log offsets how do you assign them to a JPEG?

    • MR60

      @Mountains:

      1. Yes it is

      2. Yes it is more precise than a builtin GPS

      3. If you use the georef tool in mission planner it will automatically add the GPS coordinates in your pictures (in the exif part).

      • Developer

        +1,

        Just adding to #3, the georef tool uses the time the picture was taken at and the time for each point in the log file to match the picture to the coordinates. You have to change the estimated offset time to match the offset time of the GPS time vs the Camera time in order to get a correct geotag. If your camera has GPS you can set the camera clock to the GPS time and this will reduce the error in this process.

        Jaime

        • MR60

          What I like to do also is to take a picture of my GPS showing the GPS UTC time. Then I know the precise offset by comparing the photographed time of the GPS with the time in the exif of the picture (exif viewers are available free online).

          • Jaime,

            Is it easy to detect errors when your camera time is not perfectly synced with GPS and APM time?

            Trying to learn as much as possible.  Thanks for your responses.

            Jason

            • I think you can detect large errors easily, once the geotagging is done there is a KML file generated, you can open that in google earth and when you put your mouse over one of the pictures, you can see if it matches the location. But for small errors, I am not sure how you can detect an error. Maybe some one else has an idea.

  • When I did this once for test purpose I saw in the manual a way of getting a log and testing to get the correct offset params.

  • MR60

    Hi,

    Starting too to georef my pictures. I have the same question as yours. How did you find out the right Log offsets? Do you know their meaning?

    • The log offsets shown tell Mission Planner the position of each item in the log file. So the time is the second item, latitude the 6th item and so on. 

      Currently on the new version of mission planner I had not had to modify these anymore. The default work, this problem was fixed in later versions than the one mentioned above. 

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