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Is this shift normal when adding GCP?

Please see the difference in elevation between the Initial Position and the “Capture Position”  Prior to adding GCP they were both co-planar in the Z. 

Is this normal and if so why - or how should I be interpreting this?
Model looks otherwise correct.

Second Image shows a computed Position and the Z is correct. I flew this using the pix4d app at 210’ AGL.

Thank you 

 

Just the usual garbage Z coordinate from DJI equipment…but as you can see, Pix4D fixed it all up just fine.

Adam Jordan, Is this your assumption or are you getting the same result?
Can someone form pix4d comment please?

It is no assumption, look at your Z coordinate in the original pics…were you flying negative from takeoff?

This has been seen many times and is 100% a DJI issue.

@Cesar Rullier, the vertical offset between the initial position of your images (blue) and the computed position of your images (green) and an expected, though not ideal, behavior. As Jordan pointed out, the initial position of your image, DJI_0047.JPG, is 12.65 below mean sea level while the computed elevation is 210.50 feet above mean sea level. Unfortunately, you are not the only person who has experienced the same vertical offset. The vertical offset in your image geotags is one of the reasons we recommend that you at least consider incorporating 3D ground control points for any Pix4D project.

I understand that the offset can look strange, and may even make navigating through your scene difficult, which is why I recommend that you hide the _Initial Position _and Position Error for your images in Camera Display Properties after verifying that your images are in the correct position.

If you would like a second opinion, please consider verifying the reported elevation of your images’ geotag in a third party software, e.g. Windows Explorer.

@Jordan, thank you very much for your contribution.

@Andrew, the images you are seeing are incorporating 3D GCP.
The 210’ AMSL make sense as that was the flight elevation I programmed.

So in the end do you concur that this is a DJI altimeter error when geotagging the images?

@Cesar, I believe that the elevation or altitude that is reported in DJI’s geotags is the primary source of the vertical offset that you are seeing in your reconstruction. However, I recommend that you take the opportunity to sanity-check my opinion by confirming your image’s reported elevation or altitude in a third party software. You can easily do that by right-clicking on the image in Windows Explorer, selecting Properties, and then scrolling down to the image’s GPS information.

Please let us know if you find that the elevation or altitude reported by Windows Explorer’s Properties menu is at or around 210 feet above mean sea level.

@Andrew

I looked at one of the photos as you suggested. I am converting the information to FT. However what I cannot explain is why the Altitude is NEGATIVE inside pix4D.

Hey Cesar, thank you for sharing a screenshot of your image’s properties. As you can see, the altitude reported in the image’s EXIF is significantly lower than it should be based on the altitude that was computed after you registered your images to your ground contrl points.

The initial image altitude reported in Pix4D is negative because Pix4D Desktop automatically applies a geoid model to the image’s initial position. Pix4D Desktop automatically applies a geoid offset to your image’s initial position because of our understanding of how the image’s initial position is defined in the image’s EXIF.

You can remove the geoid offset that is applied to your image’s initial position via the Image Geolocation Coordinate System menu, which is available in the Image Properties Editor. If you Reoptimize the project after removing the geoid offset you should see that the initial image position reported in the rayCloud matches what is reported in the image’s EXIF.

Some people prefer to remove the geoid offset that is applied to their images’ initial position because they find that it is easier to incorporate their ground control points. No need to wonder if your images are at the correct altitude because your project contains ground control points and you can clearly see that the image’s computed elevation has been shifted upwards to align with your ground control points.