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  1. r62ewa

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    I have been using my Phantom 4 to capture images for processing in Pix4D, the photogrammetry software and I have an issue with some of my images being read with negative elevation values by the program.

    The elevation information in the photo Properties seems to be okay but when read by Pix4D the elevation is read as negative and it only seems to occur so far with POI captured images. Has anyone else used Pix4D and had this issue occur using their Phantom 4?

    Thanks.
     
  2. Meta4

    Meta4 Moderator
    Staff Member

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    What is shown in the Exif data for these photos?
    What is the negative altitude and the actual altitude?
     
  3. r62ewa

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    In the Exif data it reads the AltitudeRef as 'Below Sea Level' and an Altitude of 37.18 m for one of my images. When Pix4D reads the image it states the image is -37.18 m. For a small sample project I have changed the AltitudeRef to 'Above Sea Level' but it still reads -37.18 m in Pix4D. I have then manually removed the '-' in Pix4D but this is not reasonable with my latest project of over 700 images. I don't know why if all images are stored as 'Below Sea Level' in the Exif, why only some would be read by Pix4D as negative while others are not. Is it due to vertical GPS error at a certain location?
     
  4. jephoto

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    Did you take any photos while on the ground to see how it reads?
    Since the last firmware update on my P3's I only get MSL altitude readouts so my on the ground shot my show an elevation of say 595' at the lakefront in Chicago.

    Did some flying at the Salton Sea in California in March new started out on the ground BELOW sea level there. ...


    Sent from my iPhone using PhantomPilots mobile app
     
  5. r62ewa

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    I have not tried taking photos on the ground. I have a colleague who uses a P4 for Photogrammetry as well and he said he has never had any issue with the image elevations being negative.

    I contacted Pix4D support and they stated it is an issue with how DJI stores the data in the EXIF file and how it is now stored as Below Sea Level. Still strange that only some of my images are being read as negative.

    I'll have to do more digging.
     
  6. WilsonFlyer

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    I assume you've tried changing the "-" to a "+" just to see as well as just removing it?
     
  7. UAV-ACE

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    Location:
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    This happens to me as well on my P4. The first projects I created were all negative values. I have since shot in ground control points (white and orange tiles) to set the elevation and use them to adjust the negative elevations into a usable orthomosaic and DSM..
     
  8. r62ewa

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    I haven't tried adding a '+' as none of the images have a '+' stored in the EXIF file to represent a positive elevation. I'd really like a solution or to figure out why some are stored as negative as having to manually change the EXIF file for hundreds of images is not practical. I have an EXIF editor that sells an Add-on to batch edit images but I'd rather just figure out the reason to see if it can fixed as opposed to having to edit later.
     
  9. r62ewa

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    What are you using to collect your GCPs?
     
  10. UAV-ACE

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    Location:
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    I have access to Trimble R10 and R8 rovers and use VRS correction for real XYZ locations. The projects are a little over 1/10th of a foot... 1.35.... that is what Pix4D is kicking out....